cell

cell:

see battery, electricbattery, electric,
device that converts chemical energy into electrical energy, consisting of a group of electric cells that are connected to act as a source of direct current.
..... Click the link for more information. .

cell,

in biology, the unit of structure and function of which all plants and animals are composed. The cell is the smallest unit in the living organism that is capable of integrating the essential life processes. There are many unicellular organisms, e.g., bacteriabacteria
[pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera.
..... Click the link for more information. and protozoansprotozoan
, informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies and that show no differentiation into tissues.
..... Click the link for more information. , in which the single cell performs all life functions. In higher organisms, a division of labor has evolved in which groups of cells have differentiated into specialized tissuestissue,
in biology, aggregation of cells that are similar in form and function and the intercellular substances produced by them. The fundamental tissues in animals are epithelial, nerve, connective, and muscle tissue; blood and lymph are commonly classed separately as vascular
..... Click the link for more information. , which in turn are grouped into organs and organ systems.

Cells can be separated into two major groups—prokaryotes, cells whose DNA is not segregated within a well-defined nucleus surrounded by a membranous nuclear envelope, and eukaryoteseukaryote
, a cell or organism composed of cells that have a membrane-bound nucleus and organelles (mitochondria, chloroplasts; see cell, in biology) and genetic material organized in chromosomes in which the DNA is combined with histone proteins.
..... Click the link for more information. , those with a membrane-enveloped nucleus. The cyanobacteria and bacteria (kingdom MoneraMonera,
taxonomic kingdom that comprises the prokaryotes (bacteria and cyanobacteria). Prokaryotes are single-celled organisms that lack a membrane-bound nucleus and usually lack membrane-bound organelles (mitochondria, chloroplasts; see cell, in biology).
..... Click the link for more information. ) are prokaryotes. They are smaller in size and simpler in internal structure than eukaryotes and are believed to have evolved much earlier (see evolutionevolution,
concept that embodies the belief that existing animals and plants developed by a process of gradual, continuous change from previously existing forms. This theory, also known as descent with modification, constitutes organic evolution.
..... Click the link for more information. ). All organisms other than cyanobacteria and bacteria consist of one or more eukaryotic cells.

All cells share a number of common properties; they store information in genesgene,
the structural unit of inheritance in living organisms. A gene is, in essence, a segment of DNA that has a particular purpose, i.e., that codes for (contains the chemical information necessary for the creation of) a specific enzyme or other protein.
..... Click the link for more information. made of DNA (see nucleic acidnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
..... Click the link for more information. ); they use proteinsprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
..... Click the link for more information. as their main structural material; they synthesize proteins in the cell's ribosomes using the information encoded in the DNA and mobilized by means of RNA; they use adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
..... Click the link for more information. as the means of transferring energy for the cell's internal processes; and they are enclosed by a cell membrane, composed of proteins and a double layer of lipidlipids,
a broad class of organic products found in living systems. Most are insoluble in water but soluble in nonpolar solvents. The definition excludes the mineral oils and other petroleum products obtained from fossil material.
..... Click the link for more information. molecules, that controls the flow of materials into and out of the cell.

Cell Structure

In a eukaryotic cell's nucleus the DNA, along with certain proteins, is arranged in long, thin threads called chromatin fibers that coil into bodies called chromosomeschromosome
, structural carrier of hereditary characteristics, found in the nucleus of every cell and so named for its readiness to absorb dyes. The term chromosome
..... Click the link for more information. during meiosismeiosis
, process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells (ovum and sperm), are being formed.
..... Click the link for more information. . The nucleus also contains one or more nucleoli (sing., nucleolus) that participate in the production on the RNA of ribosomes. The portion of the cell outside the nucleus, called the cytoplasm, contains several additional cell structures (often called organelles). Among the important organelles that may be present are the ribosomes; the endoplasmic reticulum, a highly convoluted system of membranes believed to be continuous with the nuclear envelope and responsible for transporting certain newly made proteins; the mitochondria, which are present in nearly all eukaryotic cells and extract energy by breaking down the chemical bonds in molecules of complex nutrients during respiration and perform other functions; the chloroplasts, which are present only in green plants and convert energy from sunlight by the process of photosynthesisphotosynthesis
, process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Some of the plants that lack chlorophyll, e.g.
..... Click the link for more information. ; lysosomes, which contain digestive enzymes; peroxisomes, which contain a number of specialized enzymes; the centrosomes, which function during cell division; the Golgi apparatus, which functions in the synthesis, storage, and secretion of various cellular products; filaments and microtubules that form a sort of skeletal system known as a cytoskeleton and also participate in movement of cells and organelles; vacuoles containing food in various stages of digestion (see endocytosisendocytosis
, in biology, process by which substances are taken into the cell. When the cell membrane comes into contact with a suitable food, a portion of the cell cytoplasm surges forward to meet and surround the material and a depression forms within the cell wall.
..... Click the link for more information. ); and inert granules and crystals. In plant cells there is, in addition to the cell membrane, a thickened cell wall, usually composed chiefly of cellulosecellulose,
chief constituent of the cell walls of plants. Chemically, it is a carbohydrate that is a high molecular weight polysaccharide. Raw cotton is composed of 91% pure cellulose; other important natural sources are flax, hemp, jute, straw, and wood.
..... Click the link for more information. secreted by the cell.

The Study of Cells

Because almost all cells are microscopic, knowledge of the component cell parts increased proportionately to the development of the microscopemicroscope,
optical instrument used to increase the apparent size of an object. Simple Microscopes

A magnifying glass, an ordinary double convex lens having a short focal length, is a simple microscope. The reading lens and hand lens are instruments of this type.
..... Click the link for more information. and other specialized instruments and of allied experimental techniques. Among those who contributed to early knowledge of cells through their use of the microscope were Antony van LeeuwenhoekLeeuwenhoek, Antony van
, 1632–1723, Dutch student of natural history and maker of microscopes, b. Delft. His use of lenses in examining cloth as a draper's apprentice probably led to his interest in lens making.
..... Click the link for more information. , Robert HookeHooke, Robert
, 1635–1703, English physicist, mathematician, and inventor. He became curator of experiments for the Royal Society (1662), professor of geometry at Gresham College (1665), and city surveyor of London after the great 1666 fire.
..... Click the link for more information. , and Marcello MalpighiMalpighi, Marcello
, 1628–94, Italian anatomist. A pioneer in the use of the microscope, he made many valuable observations on the structure of plants and animals.
..... Click the link for more information. . In the 19th cent. Matthias J. SchleidenSchleiden, Matthias Jakob
, 1804–81, German botanist. He was professor at the universities of Jena (1839–63) and Dorpat (1863–64). With Theodor Schwann, he is credited with establishing the foundations of the cell theory.
..... Click the link for more information. and Theodor SchwannSchwann, Theodor
, 1810–82, German physiologist and histologist. He was a student of J. P. Müller and professor at the universities of Louvain (1838–48) and Liège (from 1848).
..... Click the link for more information. developed what is now known as the cell theory. The theory was widely promoted after the pronouncement by Rudolf Virchow in 1855 that "omnis cellulae e cellula" [All cells arise from cells]. The study of cell structure came to be called cytology and that of tissues histology. In the 20th cent. appreciation of the biochemistry of the cell has flourished, along with a better understanding of its structure; cell biology now integrates both chemical and structural information.

See also biochemistrybiochemistry,
science concerned chiefly with the chemistry of biological processes; it attempts to utilize the tools and concepts of chemistry, particularly organic and physical chemistry, for elucidation of the living system.
..... Click the link for more information. .

Bibliography

See L. Thomas, The Lives of a Cell (1974); D. M. Prescott, Cells (1988); B. Alberts et al., Molecular Biology of the Cell (2d ed. 1989); J. M. Lackie and J. A. Dowe, ed., The Dictionary of Cell Biology (1989).

Cell (biology)

Cells can be separated into prokaryotic and eukaryotic categories. Eukaryotic cells contain a nucleus. They comprise protists (single-celled organisms), fungi, plants, and animals, and are generally 5–100 micrometers in linear dimension. Prokaryotic cells contain no nucleus, are relatively small (1–10 μm in diameter), and have a simple internal structure. They include two classes of bacteria: eubacteria (including photosynthetic organisms, or cyanobacteria), which are common bacteria inhabiting soil, water, and larger organisms; and archaebacteria, which grow under unusual conditions. See Eukaryotae, Prokaryotae

Prokaryotic (bacterial) cells

All eubacteria have an inner (plasma) membrane which serves as a semipermeable barrier allowing small nonpolar and polar molecules such as oxygen, carbon dioxide, and glycerol to diffuse across (down their concentration gradients), but does not allow the diffusion of larger polar molecules (sugars, amino acids, and so on) or inorganic ions such as Na⁺, K⁺, Cl^-, Ca²⁺ (sodium, potassium, chlorine, calcium). The plasma membrane, which is a lipid bilayer, utilizes transmembrane transporter and channel proteins to facilitate the movement of these molecules. Eubacteria can be further separated into two classes based on their ability to retain the dye crystal violet. Gram-positive cells retain the dye; their cell surface includes the inner plasma membrane and a cell wall composed of multiple layers of peptidoglycan. Gram-negative bacteria are surrounded by two membranes: the inner (plasma) membrane and an outer membrane that allows the passage of molecules of less than 1000 molecular weight through porin protein channels. Between the inner and outer membranes is the peptidoglycan-rich cell wall and the periplasmic space. See Cell permeability

Eubacteria contain a single circular double-stranded molecule of deoxyribonucleic acid (DNA), or a single chromosome. As prokaryotic cells lack a nucleus, this genomic DNA resides in a central region of the cell called the nucleoid. The bacterial genome contains all the necessary information to maintain the structure and function of the cell.

Artist's rendition of a eukaryotic animal cell

Many bacteria are able to move from place to place, or are motile. Their motility is based on a helical flagellum composed of interwoven protein called flagellin. The flagellum is attached to the cell surface through a basal body, and propels the bacteria through an aqueous environment by rotating like the propeller on a motor boat. The motor is reversible, allowing the bacteria to move toward chemoattractants and away from chemorepellants.

Eukaryotic cells

In a light microscopic view of a eukaryotic cell, a plasma membrane can be seen which defines the outer boundaries of the cell, surrounding the cell's protoplasm or contents. The protoplasm includes the nucleus, where the cell's DNA is compartmentalized, and the remaining contents of the cell (the cytoplasm). The eukaryotic cell's organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, cytoskeleton, and plasma membrane (Fig. 1). The organelles occupy approximately half the total volume of the cytoplasm. The remaining compartment of cytoplasm (minus organelles) is referred to as the cytosol or cytoplasmic ground substance. Eukaryotic cells also differ from prokaryotic cells in having a cytoskeleton that gives the cell its shape, its capacity to move, and its ability to transport organelles and vesicles from one part of the cell cytoplasm to another. Eukaryotic cells are generally larger than prokaryotic cells and therefore require a cytoskeleton and membrane skeleton to maintain their shape, which is related to their functions.

Artist's rendition of a typical plant cell

Eukaryotic cells contain a large amount of DNA (about a thousandfold more than bacterial cells), only approximately 1% of which encodes protein. The remaining DNA is structural (involved in DNA packaging) or regulatory (helping to switch on and off genes).

Plasma membrane

The plasma membrane serves as a selective permeability barrier between a cell's environment and cytoplasm. The fundamental structure of plasma membranes (as well as organelle membranes) is the lipid bilayer, formed due to the tendency of amphipathic phospholipids to bury their hydrophobic fatty acid tails away from water. Human and animal cell plasma membranes contain a varied composition of phospholipids, cholesterol, and glycolipids. See Cell membranes

Cytoskeleton

The cytoskeleton is involved in establishing cell shape, polarity, and motility, and in directing the movement of organelles within the cell. The cytoskeleton includes microfilaments, microtubules, intermediate filaments, and the two-dimensional membrane skeleton that lines the cytoplasmic surface of cell membranes. See Cytoskeleton

Nucleus

One of the most prominent organelles within a eukaryotic cell is the nucleus. The nuclear compartment is separated from the rest of the cell by a specialized membrane complex built from two distinct lipid bilayers, referred to as the nuclear envelope. However, the interior of the nucleus maintains contact with the cell's cytoplasm via nuclear pores. The primary function of the nucleus is to house the genetic apparatus of the cell; this genetic machinery is composed of DNA (arranged in linear units called chromosomes), RNA, and proteins. Nuclear proteins aid in the performance of nuclear functions and include polypeptides that have a direct role in the regulation of gene function and those that give structure to the genetic material. See Cell nucleus

Endoplasmic reticulum

The endoplasmic reticulum is composed of membrane-enclosed flattened sacs or cisternae. The enclosed compartment is called the lumen. The endoplasmic reticulum is morphologically separated into rough (RER) and smooth (SER). PER is studded with ribosomes and SER is not. RER is the site of protein synthesis, while lipids are synthesized in both RER and SER. See Endoplasmic reticulum

Golgi apparatus

The final posttranslational modifications of proteins and glycolipids occur within a series of flattened membranous sacs called the Golgi apparatus. Vesicles which bud from the endoplasmic reticulum fuse with a specialized region of the cis Golgi compartment called the cis Golgi network. In the trans Golgi network, proteins and lipids are sorted into transport vesicles destined for lysosomes, the plasma membrane, or secretion. See Golgi apparatus

Lysosomes

Lysosomes are membrane-bound organelles with a luminal pH of 5.0, filled with acid hydrolyses. Lysosomes are responsible for degrading materials brought into the cell by endocytosis or phagocytosis, or autophagocytosis of spent cellular material. See Endocytosis, Lysosome

Mitochondria

The mitochondrion contains a double membrane: the outer membrane, which contains a channel-forming protein named porin, and an inner membrane, which contains multiple infolds called cristae. The inner membrane, which contains the protein complexes responsible for electron transport and oxidative phosphorylation, is folded into numerous cristae that increase the surface area per volume of this membrane. The transfer of electrons from nicotinamide adenine dinucleotide (NADH) or flavin adenine dinucleotide (FADH₂) down the electron transfer chain to oxygen causes protons to be pumped out of the mitochondrial matrix into the intermembrane space. The resulting proton motive force drives the conversion of ADP plus inorganic orthophosphate (P_i) to ATP by the enzyme ATP synthetase. See Mitochondria

Peroxisomes

Within the peroxisome, hydrogen atoms are removed from organic substrates and hydrogen peroxide is formed. The enzyme catalase can then utilize the hydrogen peroxide to oxidize substrates such as alcohols, formaldehydes, and formic acid in detoxifying reactions. See Peroxisome

Plant cells

Plant cells are distinguished from other eukaryotic cells by various features. Outside their plasma membrane, plant cells have an extremely rigid cell wall. This cell wall is composed of cellulose and other polymers and is distinct in composition from the cell walls found in fungi or bacterial cells. The plant cell wall expands during cell growth, and a new cell wall partition is created between the two daughter cells during cell division. Similar cell walls are not observed in animal cells (Fig. 2).

Most plant cells contain membrane-encapsulated vacuoles as major components of their cytoplasm. These vacuoles contain water, sucrose, ions, nitrogen-containing compounds formed by nitrogen fixation, and waste products.

Chloroplasts are the other major organelle in plant cells that is not found in other eukaryotic cells. Like mitochondria, they are constantly in motion within the cytoplasm. One of the pigments found in chloroplasts is chlorophyll, which is the molecule that absorbs light and gives the green coloration to the chloroplast. Chloroplasts, like mitochondria, have an outer and inner membrane. Within the matrix of the chloroplast there is an intricate internal membrane system. The internal membranes are made up of flattened interconnected vesicles that take on a disc-like structure (thylakoid vesicles). The thylakoid vesicles are stacked to form structures called grana, which are separated by a space called the stroma. Within the stroma, carbon dioxide (CO₂) fixation occurs, in which carbon dioxide is converted to various intermediates during the production of sugars. Chlorophyll is found within the thylakoid vesicles; it absorbs light and, with the involvement of other pigments and enzymes, generates ATP during photosynthesis. See Plant cell

cell

(mirror cell) The enclosure that holds the primary mirror in a reflecting telescope. It must hold the mirror so that the collimation of the optical elements is maintained as the direction of observation changes. It must also support the mirror so that it does not sag to an unacceptable degree under its own weight. Without carefully designed support over the whole rear face the mirror of the 5-meter Hale telescope would sag by 0.0625 mm, which is about 500 times the allowable quarter wave limit. The cell is usually provided with a closure or lid that protects the optical surface when the telescope is not in use.

Cell

A small compartment, such as a room in a dormitory, but especially a confined study-bedroom allotted to a monk or nun in a monastery.

Cell

an elementary living system capable of independent existence and self-replication and development; the basis of the structure and life processes of all animals and plants.

Cells exist both as independent organisms (protozoans) and as component elements of multicellular organisms (tissue cells). The term “cell” was proposed by the English microscopist R. Hooke in 1665. The cell is the object of study of a special branch of biology called cytology. Systematic study of the cell did not begin until the 19th century; one of the most important scientific generalizations of that time was the cell theory, which asserted the structural unity of all living things. The study of life at the cellular level is the basis of contemporary biological research.

The structure and functions of each cell show certain characteristics common to all cells, reflecting a common origin from primary organic complexes. The specific features of various cells are the result of specialization in the process of evolution. All cells similarly regulate metabolism, duplicate and use hereditary material, and acquire and utilize energy. At the same time, various unicellular organisms (amoebas, infusorians) differ sharply in terms of size, shape, and behavior. No less diverse are the cells of multicellular organisms. For example, in man, lymphoid cells are small (about 10 microns in diameter) and rounded and participate in immunological reactions, whereas some nerve cells have appendages more than a meter long and perform the body’s basic regulatory functions.

Research methods. The first cytological method was the use of microscopy with living cells. Present-day variants of light microscopy, such as phase-contrast, luminescent, and interference microscopy, make it possible to study the shape of the cell, the general structure of some of its elements, the movement of cells, and cell division. The details of cell structure can be revealed only after special contrasting, which is achieved by staining the killed cell.

A new stage in the study of cell structure is the use of the electron microscope, which has the advantage of considerably greater resolution of cell structures than the light microscope. The chemical composition of the cell is studied by cytochemical and histochemical methods, making it possible to reveal the localization and concentration of various substances in cellular structures, the intensity of synthesis of these substances, and the movement of the substances within the cell. Cytophysiological methods make it possible to study certain functions of the cell, such as excitation and secretion.

General properties. Every cell has two principal parts—the nucleus and the cytoplasm. Within each of these it is possible to distinguish certain substructures, which differ in shape, size, internal structure, chemical properties, and function. Some of these, called organoids, are vital to the cell and in fact are found in all cells. Others are the products of cell activity and represent temporary formations. The segregation of various biochemical functions takes place by means of these specialized structures, facilitating the accomplishment within the same cell of diverse processes, including the synthesis and decomposition of many substances.

Genetic information on the structure of the proteins characteristic of an organism of a particular species is stored in DNA (deoxyribonucleic acid), the principal component of nuclear organoids called chromosomes. Another, most important property of DNA is its capacity for self-replication, which ensures both the stability of the hereditary information and its continuity— that is, its transmission to succeeding generations.

Ribonucleic acids, the immediate participants in protein synthesis, are synthesized on limited sections of the DNA molecule (embracing several genes), which act as templates. The transcription of the DNA code is accomplished by the synthesis of messenger RNA (m-RNA). Protein synthesis is, in effect, a reading of information from the RNA template. This process, called translation, involves the participation of transfer RNA (t-RNA) and special organoids, called ribosomes, that are formed in the nucleolus. The size of the nucleolus is a function chiefly of the cell’s ribosome requirement; the nucleolus is, therefore, especially large in a cell that intensively synthesizes proteins. Protein synthesis, the end result of chromosome function, occurs mainly in the cytoplasm.

In the final analysis, proteins (comprising enzymes, components of cell structures, and the regulators of various processes, including transcription itself) determine all aspects of cell life, permitting the cell to preserve its individuality despite its constantly changing surroundings. Whereas the bacterial cell may synthesize about 1,000 different proteins, almost every human cell synthesizes more than 10,000. Thus, the diversity of intracellular processes increases substantially in the course of evolution.

The sheath surrounding the nucleus, which separates the nuclear content from the cytoplasm, actually consists of two membranes, both of which are perforated by pores—specialized areas for the transport of certain compounds from the nucleus into the cytoplasm and vice versa. Other substances pass through the membranes by means of diffusion or active transport, the latter process requiring the expenditure of energy.

Many processes occur in the cytoplasm with the participation of the membranes of the endoplasmic reticulum (the principal synthesizing system of the cell), the Golgi apparatus, and the mitochondria. The differences in the membranes of various organoids are determined by the properties of the proteins and lipids that form them. Ribosomes are attached to some of the membranes of the endoplasmic reticulum. These are the site of intensive protein synthesis. This type of granular endoplasmic reticulum is especially well developed in secretory cells or in cells that intensively renew proteins, such as human liver cells, pancreas cells, and nerves. Other biological membranes that are lacking in ribosomes (smooth reticulum) are made up in part of enzymes that participate in the synthesis of carbohydrate-protein and lipid complexes. The products of cell activity may accumulate temporarily in the canals of the endoplasmic reticulum; in some cells the substances are actually transported through these canals.

Before being carried out of the cell, substances are concentrated in the lamellar Golgi apparatus, which isolates various cell inclusions, such as secretory or pigment granules, and in which lysosomes are formed (sacs containing hydrolytic enzymes and participating in the intracellular digestion of many substances). The system of canals, vacuoles, and sacs, all surrounded by membranes, acts as an integrated unit; the endoplasmic reticulum can, without interruption, connect to the membranes surrounding the nucleus, unite with the cytoplasmic membrane, and form the Golgi complex. However, these connections are not stable. Often (in many cells, usually), the various membranous structures are discrete and exchange substances through the hyaloplasm.

Cell energetics depends to a large extent on the work of the mitochondria. The number of mitochondria varies in different types of cells from dozens to several thousand. For example, there are about 2,000 mitochondria in the human liver cell, and their total volume is no less than one-fifth the volume of the cell. The outer membrane of the mitochondrion separates it from the cytoplasm. The basic energy conversions of substances occur on the inner membrane. A result of these conversions is the formation of a compound rich in energy—adenosine triphosphoric acid (ATP)—the universal carrier of energy in the cell. Mitochondria contain DNA and are capable of self-replication. However, the autonomy of the mitochondria is relative: their reproduction and activities depend on the nucleus. Various syntheses, the transport and excretion of substances, mechanical work, and the regulation of processes in the cell are performed using the energy of ATP.

Certain structures that look like tiny (submicroscopic) tubules participate in cell division and, sometimes, in cell movement. The assembling and functioning of such structures depend on the centrioles. The spindle, operative in cell division, is organized with the participation of the centriole. The spindle, in turn, participates in the translocation of chromosomes and the orientation of the axis of cell division. The basal bodies, derivatives of the centrioles, are necessary for the construction and normal functioning of flagella and cilia, locomotor and sensory formations of the cell whose structure is the same in protozoans and various metazoan cells.

The cell is separated from the extracellular medium by the plasma membrane, through which ions and molecules enter the cell and are excreted from it. The ratio of the cell’s surface to its volume decreases as cell volume increases; the larger the cell, the more difficult are its connections with the external medium. The size of a cell, therefore, is necessarily limited.

Active ion transfer, which requires the expenditure of energy and requires special enzymes and, possibly, carrier agents, is characteristic of living cells. Because of the active and selective transfer of certain ions into the cell and the continuous removal of others from it, a difference is created between the ion concentration within the cell and that of the surrounding medium. This effect may be caused by the bonding of ions with cell components. Many ions are necessary as activators of intracellular syntheses and as stabilizers of the structure of the organoids. Reversible changes in the ratio of the ions within the cell to those in the medium are the basis of the cell’s bioelectric activity—one of the most important factors in the transmission of signals from one cell to another.

The plasma membrane, by forming invaginations which then close up and break off as bubbles within the cell, is capable of capturing solutions of large molecules (pinocytosis) or even certain particles with diameters to several microns (phagocytosis). It is in this way that some cells are nourished, that some substances are transferred through the cells, and that bacteria are captured by phagocytes. The cohesive forces that in many cases keep cells close to one another (for example, the integuments of the body or internal organs) are also associated with the properties of the plasma membrane. Cellular cohesion and intercommunication are ensured by the chemical interactions of the membranes and by special structures of the membrane called desmosomes.

The structural scheme of cell, discussed in its general form, is characteristic in its basic features of both animal cells and plant cells. However, there are essential differences in the characteristics of the metabolism and structure of plant cells and animal cells.

Plant cells. As a rule, the plasma membranes of plant cells are covered with a rigid outer sheath (possibly absent only in the germ cells) consisting in the majority of plants mainly of polysaccharides: cellulose, pectic substances, hemicelluloses, and, in fungi and some algae, chitin. These cell walls are supplied with pores through which, by means of cytoplasmic outgrowths, neighboring cells can communicate with one another. The composition and structure of the wall change with the growth and development of the cell. In cells that have ceased growing, the envelope often becomes impregnated with lignin, silica, or other toughening matter.

The cell walls determine the mechanical properties of the plant. The cells of certain plant tissues have especially thick and sturdy walls that retain their skeletal functions even after the death of the cell (wood). Differentiated plant cells have several vacuoles or a single central vacuole that usually occupies the greater part of the cell’s volume. The vacuoles contain a solution of various salts, carbohydrates, organic acids, alkaloids, amino acids, and proteins, as well as a reserve of water. Nutritive substances may also be deposited in the vacuoles. The cytoplasm of plant cells contains special organoids, or plastids, including leucoplasts (in which starch is often deposited), chloroplasts (containing predominantly chlorophyll and responsible for photosynthesis), and chromoplasts (containing carotenoid pigments). Both plastids and mitochondria are capable of self-replication. The Golgi apparatus in plant cells is represented by dictyosomes, which are dispersed throughout the cytoplasm.

Unicellular organisms. The structure and functions of unicellular organisms, or protozoans, combine the features characteristic of any cell with features of independent organisms. Thus, protozoans have the same set of organoids as do the cells of metazoans, the ultrastructure of their organoids is identical, and typical chromosomes are found when protozoans divide. However, the adaptation of protozoans to a variety of modes of life (aquatic or terrestrial, free-living or parasitic) has made for considerable diversity in their structure and physiology. Many protozoans, such as flagellates and infusorians, have a complex motor apparatus and organelles associated with the capture of food and digestion. The study of protozoans is of great interest in uncovering the phylogenetic possibilities of the cell, since evolutionary changes in the organism occur on the cellular level.

Unlike protozoans and the cells of metazoans, bacteria, blue-green algae, and actinomycetes do not have a formed nucleus and chromosomes. Their genetic apparatus, called a nucleoid, is represented by threads of DNA and is not enclosed in a membrane. Even more different from the cells of metazoans and protozoans are the viruses, in which the basic enzymes necessary for metabolism are absent. For this reason viruses can grow and reproduce only by penetrating other cells and making use of their enzyme systems.

Special functions. During the course of metazoan evolution there arose a division of functions between cells, which in turn led to a broadening of the adaptive possibilities of animals and plants to changing environmental conditions. The genetically fixed differences in the shape, size, and aspects of the metabolism of cells are realized during the process of individual development. The principal manifestation of development is cell differentiation—the structural and functional specialization of the cell. Differentiated cells have the same set of chromosomes as the fertilized egg cell; this is proved by the fact that after the nucleus of a differentiated cell is transplanted into an egg cell from which the nucleus has been removed, a complete organism is able to develop. Thus, the differences between differentiated cells are apparently determined by various interrelationships between active and inactive genes, each of which codes the biosynthesis of a particular protein.

Judging by the composition of these proteins, only a small proportion (about 10 percent) of the genes characteristic of the cells of a given species are active (that is, capable of transcription) in differentiated cells. Of these genes, only a few are responsible for the specialized function of the cell, while the rest provide for general cellular functions. For example, in muscle cells, genes are active that code the structure of contractile proteins, and in erythroid cells, genes are active that code the biosynthesis of hemoglobin. However, in every cell the genes that determine the biosynthesis of the substances and structures necessary to all cells, such as the enzymes that participate in energy conversions, must also be active. In the process of cell specialization, certain general cellular functions may develop especially strongly. For example, in gland cells, synthetic activity is most strongly expressed; muscle cells are the most contractile; nerve cells are the most excitable. Narrowly specialized cells contain structures that are peculiar to themselves (for example, in animals, the myofibrils of muscles, the tonofibrils and cilia of certain integumentary cells, and the neurofibrils of nerve cells; in protozoans or the spermatozoa of metazoans, flagella). Sometimes specialization is accompanied by the loss of certain properties (for example, nerve cells lose their capacity to reproduce; the mature cell nuclei of mammalian intestinal epithelium cannot synthesize RNA; the mature erythrocytes of mammals lack nuclei).

The performance of functions important to the organism sometimes includes the death of the cell. Thus, cells of the epidermis gradually cornify and die but remain for some time in a thin layer protecting the underlying tissues from damage and infection. Cells in the sebaceous glands gradually turn into drops of fat, which is then either utilized by the body or excreted.

Noncellular structures are also formed by the cell in order to perform certain tissue functions. The principal means of their formation are secretion or the transformation of cytoplasmic components. For example, a large proportion of the volume of subcutaneous tissue, cartilage, and bone is interstitial matter— a derivative of connective-tissue cells. Blood cells are found in a fluid medium (blood plasma) that contains proteins, sugars, and other substances produced by various cells of the body. Epithelial cells, which form a sheet, are surrounded by a thin interlayer of diffusely distributed substances. Chief among these are glycoproteins (so-called cement, or supramembranal component). The outer coverings of arthropods and the shells of mollusks are also products of cellular secretion.The interaction of specialized cells is a necessary condition for the life of the organism and often for the cells themselves. Deprived of communication with one another (for example, in culture), cells rapidly lose their characteristic features of specialized function.

Cell division. The basis of the cell’s capacity to reproduce itself is the unique property of DNA to copy itself and the strictly equal division of the reproduced chromosomes in the process of mitosis. The result of division is the formation of two cells that are identical to the original in genetic properties and contain both nucleus and cytoplasm. The processes of chromosomal self-replication and division, formation of two nuclei, and cytoplasmic division are distributed over time; in sum, they constitute the mitotic cycle of the cell. If the cell begins to prepare for the next division immediately after dividing, the mitotic cycle coincides with the life cycle of the cell. However, in many cases, after division (and sometimes before it) the cell emerges from the mitotic cycle, becomes differentiated, and fulfills some special function in the body. The contents of such cells may be renewed at the expense of the divisions of only slightly differentiated cells. In some tissues, differentiated cells too are capable of repeatedly entering the mitotic cycle. In nerve tissue, differentiated cells do not divide; many of them live throughout the life of the whole organism (that is, in man, several decades). Nevertheless, the nuclei of the nerve cells do not lose their capacity for division; transplanted into the cytoplasm of cancerous cells, they synthesize DNA and divide. Experiments with hybrid cells show the influence of the cytoplasm on the manifestation of nuclear functions.

Imperfect preparation for division prevents mitosis or distorts its course. Thus, in some cases, cytoplasmic division fails to take place and a binuclear cell is formed. The outcome of repeated nuclear divisions in a nondividing cell is the appearance of multinuclear cells or complex supracellular structures, or symplasts (for example, in striated muscle). Sometimes reproduction of the cell is limited to reproduction of the chromosomes, and a polyploid cell forms with a double set (compared to the parent cell) of chromosomes. Polyploidy leads to the intensification of synthetic activity and to an increase in the size and mass of the cell.

Cell renewal. In order to work properly over an extended period, every cell must have its worn-out structures restored and the externally induced damages to it eliminated. The restorative processes characteristic of all cells are associated with changes in the permeability of the plasma membrane and are accompanied by the intensification of intracellular synthesis (most importantly, of proteins). In many tissues, stimulation of the renewal processes leads to reproduction of the genetic apparatus and division of the cell; this is characteristic, for instance, of the integuments or the hemopoietic system. The processes of intracellular renewal in these tissues are weakly expressed, and their cells live a comparatively short time (for example, cells of the intestinal integument of mammals live only a few days). Intracellular renewal processes attain their maximum expression in nondividing or slowly dividing cell populations, such as nerves. The indicator of the perfection of the internal renewal processes of the cell is the cell’s life-span; for many nerve cells this coincides with the life-span of the organism itself.

Mutations. The process of DNA replication usually occurs without deviation and the genetic code remains constant, ensuring the synthesis of the same set of proteins in an enormous number of cell generations. However, in rare instances, mutation may occur—that is, a change in part of the structure of the gene. The ultimate effect of mutation is a change in the properties of the proteins coded by the mutant genes. If important enzyme systems are affected, the properties of the cell (sometimes of the entire organism) may be changed substantially. For example, mutuation of one of the genes controlling hemoglobin synthesis leads to anemia, a serious condition. Natural selection of useful mutations, on the other hand, is an important mechanism of evolution.

Regulation of cell function. The principal regulatory mechanism of the intracellular processes is associated with various influences on enzymes. Enzymes are highly specific catalysts of biochemical reactions. Regulation may be directly genetic, the composition of the enzymes or the quantity of a given enzyme in the cell being predetermined. In the case of enzyme quantity, regulation may also occur on the level of translation. Another type of regulation is influence on the enzyme itself, as a result of which the enzyme’s activity may be either inhibited or stimulated. Regulation on the structural level influences the assembly of cellular structures (membranes, ribosomes, and so forth). More concrete regulators of intracellular processes include nervous influences, hormones, special substances produced within the cell or by surrounding cells (especially proteins), or the products of the intracellular reactions themselves. In this last case, the effect is accomplished by a feedback principle in which the product of a reaction influences the activity of the enzyme that is the catalyst of the initial reaction. Other regulatory mechanisms include the transport of precursors and ions, influences on template synthesis (RNA, polysomes, synthesis enzymes), and alteration of the form of a regulated enzyme.

The organization and regulation of cell function on the molecular level determine such properties of living systems as spatial compactness and economy of energy. An important property of multicellular organisms—reliability—depends in great part on the number (interchangeability) of cells of each functional type and on the possibility of their replacement through cellular reproduction and renewal of the components of each cell.

In medicine, changes can be induced in the cell to treat and prevent various diseases. Many medicinal substances change the activity of certain cells. Narcotics, tranquilizers, and analgesics lower the intensity of neural activity; stimulants increase it. Some substances stimulate contraction of the muscle cells of the blood vessels. Others stimulate a similar reaction in the muscles of the uterus or heart. Dividing cells can be affected by radiation or cytostatic substances (blocking cell division). Immunization stimulates the activity of the lymphoid cells, which manufacture antibodies against foreign proteins, and thereby prevents a number of diseases.

REFERENCES

Kol’tsov, N. K. Organizatsiia kletki. Moscow-Leningrad, 1936.
Wilson, E. Kletka i ee rol’ v razvitii i nasledstvennosti, vols. 1–2. Moscow-Leningrad, 1936–40. (Translated from English.)
Nasonov, D. N., and V. Ia. Aleksandrov. Reaktsiia zhivogo veshchestva na vneshnie vozdeistviia. Moscow-Leningrad, 1940.
Kedrovskii, B. V. Tsitologiia belkovykh sintezov v zhivotnoi kletke. Moscow, 1959.
Mazia, D. Mitoz i fiziologiia kletochnogo deleniia. Moscow, 1963. (Translated from English.)
Rukovodstvo po tsitologii, vols. 1–2. Moscow-Leningrad, 1965–66.
Brodskii, V. Ia. Trofika kletki. Moscow, 1966.
Zhivaia kletka. Moscow, 1966. (Collection of articles; translated from English.)
DeRobertis, E., V. Nowinski, and F. Saez. Biologiia kletki. Moscow, 1967. (Translated from English.)
Vasil’ev, Iu. M., and A. G. Malenkov. Kletochnaiapoverkhnost’ i reaktsii kletok. Leningrad, 1968.
Alov, I. A., A. I. Braude, and M. E. Aspiz. Osnovy funktsional’noi morfologii kletki, 2nd ed. Moscow, 1969.
Loewy, A., and P. Siekevitz. Struktura i funktsii kletki. Moscow, 1971. (Translated from English.)
Handbook of Molecular Cytology. Edited by A. Lima-de-Faria. Amsterdam, 1969.

V. IA. BRODSKII

Cell

a living area in a monastery. Most of the Russian monasteries permitted the construction of a personal cell for each monk or nun. As a result, monks from rich families had comfortable, spacious cells.

cell

[sel] (biology) The microscopic functional and structural unit of all living organisms, consisting of a nucleus, cytoplasm, and a limiting membrane. (computer science) An elementary unit of data storage. In a spreadsheet, the intersection of a row and a column. (electricity) A single unit of a battery. (industrial engineering) A manufacturing unit consisting of a group of work stations and their interconnecting materials-transport mechanisms and storage buffers. (mathematics) The homeomorphic image of the unit ball. One of the (n- 1)-dimensional polytopes that enclose a given n-dimensional polytope. (mining engineering) A compartment in a flotation machine. (nucleonics) One of a set of elementary regions in a heterogeneous reactor, all of which have the same geometrical form and the same neutron characteristics. (physical chemistry) A cup, jar, or vessel containing electrolyte solutions and metal electrodes to produce an electric current (conductiometric or potentiometric) or for electrolysis (electrolytic).

cell

1. See core.2. A single small cavity surrounded partially or completely by walls. 3. A segment of a ribbed vault. 4. The small sleeping apartment of a monk or a prisoner. 5. In electrical systems, a single raceway of a cellular or underfloor duct system. 6. In electrical batteries, a single voltage-producing component used in series with other similar components to provide the desired output voltage.

cell

1. Biology the basic structural and functional unit of living organisms. It consists of a nucleus, containing the genetic material, surrounded by the cytoplasm in which are mitochondria, lysosomes, ribosomes, and other organelles. All cells are bounded by a cell membrane; plant cells have an outer cell wall in addition 2. Biology any small cavity or area, such as the cavity containing pollen in an anther 3. a device for converting chemical energy into electrical energy, usually consisting of a container with two electrodes immersed in an electrolyte 4. short for electrolytic cell5. a small religious house dependent upon a larger one 6. a small group of persons operating as a nucleus of a larger political, religious, or other organization 7. Maths a small unit of volume in a mathematical coordinate system 8. Zoology one of the areas on an insect wing bounded by veins

cell

(spreadsheet)In a spreadsheet, the intersection of a rowa column and a sheet, the smallest addressable unit of data.A cell contains either a constant value or a formula that isused to calculate a value. The cell has a format thatdetermines how to display the value. A cell can be part of arange. A cell is usually referred to by its column(labelled by one or more letters from the sequence A, B, ...,Z, AA, AB, ..., AZ, BA, BB, ..., BZ, ... ) and its row numbercounting up from one, e.g. cell B3 is in the second columnacross and the third row down. A cell also belongs to aparticular sheet, e.g. "Sheet 1".

cell

(networking)ATM's term for a packet.

cell

(1) A geographic area in a cellular phone system. See cellphone.

(2) In a spreadsheet, the intersection of a row and column.

(3) Short for "cellphone."

(4) An elementary unit of storage for data (bit) or power (battery).

(5) See Cell chip.

cell

(sel), 1. The smallest unit of living structure capable of independent existence, composed of a membrane-enclosed mass of protoplasm and containing a nucleus or nucleoid. Cells are highly variable and specialized in both structure and function, although all must at some stage replicate proteins and nucleic acids, use energy, and reproduce themselves. 2. A small closed or partly closed cavity; a compartment or hollow receptacle. 3. A container of glass, ceramic, or other solid material within which chemical reactions generating electricity take place or solutions are placed for photometric assays. [L. cella, a storeroom, a chamber]

cell

(sĕl)n.1. The smallest structural unit of an organism that is capable of independent functioning, consisting of cytoplasm, usually one nucleus, and various other organelles, all surrounded by a semipermeable cell membrane.2. A small enclosed cavity or space.

cell

(sel) 1. The smallest unit of living structure capable of independent existence, composed of a membrane-enclosed mass of protoplasm and containing a nucleus or nucleoid. Cells are highly variable and specialized in both structure and function, although all must at some stage replicate proteins and nucleic acids, use energy, and reproduce themselves. 2. A small closed or partly closed cavity; a compartment or hollow receptacle. 3. A container of glass, ceramic, or other solid material within which chemical reactions that generate electricity occur. [L. cella, a storeroom, a chamber]

cell

(sel) [L. cella, a chamber]

GENERALIZED HUMAN CELL AND ORGANELLES The basic unit of life. A cell is a group of self-sustaining biochemical reactions that are isolated from the environment by a selectively permeable lipid membrane. Among the key reactions are those that maintain a stable intracellular concentration of ions; for mammalian cells, typical internal concentrations include 140 mM K+, 5-15 mM Na+, 5-15 mM Cl-, and a pH of 7.2, which can be significantly different from their concentrations outside the cell. Other key reactions move molecules and molecular complexes within the cell, sometimes changing the cell's shape. These reactions, along with many others, require energy, and the generation of energy by breaking apart preexisting hydrocarbon molecules ("food") is the job of glycolysis and other characteristic intracellular metabolic reactions. See: glycolysis; metabolism; mitochondrion.

Structure

Intracellular chemical reactions are controlled by enzymes that are organized in stable molecular complexes called organelles. The polymer-based organelles include centrioles and the cytoskeleton; nucleic acid-based organelles include ribosomes; and membrane-enclosed organelles include the nucleus, endoplasmic reticula, Golgi complexes, lysosomes, peroxisomes, mitochondria, and storage and transport vesicles. See: illustrationIndividual mammalian cells are usually microscopic, typically ranging from 5 µm to 50 µm in diameter. In humans, lymphocytes are small cells (~6 µm in diameter), columnar epithelial cells (10 µm x 20 µm) are medium-size cells, and mature ova (120-150 µm) are some of the largest cells.

Cell Division

In mammals, all new cells arise from existing cells through cell division, and an animal's growth results largely from increases in the number of its cells, most of which differentiate into specialized cell types to form the body's various tissues. Cell division involves two major processes: karyokinesis, the division of the nucleus, and cytokinesis, the division of the remainder of the cell. When generating somatic daughter cells, karyokinesis uses a process called mitosis, which produces daughter cells with a full complement of chromosomes. When generating germ cells, karyokinesis includes a process called meiosis, which produces daughter cells with half the normal number of chromosomes. See: meiosis and mitosis for illus.

A cell

Alpha cell of the pancreas.

accessory cell

A monocyte or macrophage that participates in the immune response. See: antigen-presenting cell; macrophage

acidophilic cell

Acidophil.

acinar cell

A cell present in the acinus of an acinous gland, e.g., of the pancreas.

adipose cell

Adipocyte..

adult stem cell

A precursor cell that can also give rise to identical precursor cells: daughters of a stem cell can develop into a terminally-differentiated cell type or they can remain a stem cell. Adult stem cells are found in many tissues, such as bone marrow, brain, retina, skin, intestines, liver, testis, and pancreas. Synonym: somatic stem cell See: embryonic stem cell

adventitial cell

A macrophage along a blood vessel, together with perivascular undifferentiated cells associated with it.

air cell

An air-filled sinus cavity in a bone.

alpha cell

1. An enteroendocrine cell that produces glucagon and is found in the pancreatic islets. Synonym: A cell 2. An acidophil of the adenohypophysis (anterior pituitary gland).

alveolar cell

1. In the lung, either of two types of epithelial cells lining the alveoli. Type I cells are simple thin squamous epithelial cells. Type II cells secrete pulmonary surfactant. Type II cells are smaller and more numerous than Type I cells.2. In the mammary glands, the milk-secreting epithelial cells, which are activated during lactation.

amacrine cell

A modified nerve cell in the retina that has dendrites but no axon. See: neuron

ameloblast cell

Ameloblast.

anterior horn cell

A somatic motor neuron that has its cell body in the ventral (anterior) horn of the gray matter of the spinal cord; its axon passes out through a ventral root and innervates skeletal muscle.

antigen-presenting cell

Abbreviation: APC
A cell that breaks down antigens and displays their fragments on surface receptors next to major histocompatibility complex molecules. This presentation is necessary for some T lymphocytes that are unable to recognize soluble antigens. Macrophages are the primary antigen-presenting cells, but B cells and dendritic cells also can act as APCs. See: T cell; macrophage processing cell

APUD

The abbreviated name for an 'amine precursor uptake and decarboxylation cell'. These cells are the constituents of a diffuse neuroendocrine system and all have metabolic pathways that make and utilize serotonin (5-HT). APUD cells include chromaffin cells, enterochromaffin cells, and SIF cells as well as certain cells found in the parathyroid gland, thyroid gland, pituitary gland, hypothalamus, and placenta.

argentaffin cell

A cell in the epithelium of the stomach, intestines, and appendix that secretes serotonin.

astroglial cell

Astrocyte.

atypical glandular cells

Abbreviation: AGC
An abnormal finding on a Pap test. This classification is divided into “favor neoplasia” or “not otherwise specified (NOS).” NOS is subdivided into endocervical or endometrial origin. Atypical endocervical cells are important because of their risk for significant disease. Synonym: atypical glandular cells of undetermined significance

atypical glandular cells of undetermined significance

Abbreviation: AGUS
Atypical glandular cells.

B cell

1. A lymphocyte that synthesizes and secretes antibodies. B lymphocytes originate and differentiate in the bone marrow and then populate the spleen, lymph nodes, and other lymphoid tissues. When exposed to an antigen, a B cell divides to form (a) plasma cells, which produce antigen-specific antibodies, and (b) a lesser number of memory B cells, which can quickly differentiate into plasma cells upon a second exposure to the original antigen. Antibody production is a key part of the humoral immune response of adaptive immunity. The humoral immune response is effective against bacteria, viruses, and other pathogens, and provides the rationale for vaccination. Synonym: B lymphocyte See: ; T cell; 2. Pancreatic beta cell.

band cell

The developing leukocyte at a stage at which the nucleus is not segmented.

basal cell

1. A rounded or cuboidal epithelial stem cell found in the bottom layer of pseudostratified epithelia, such as the epidermis and the lining of the airways of the lung. 2. Either of two types of cell found in the bottom layer of the olfactory epithelium; one type is a flattened "basal cell proper", and the other is a rounded stem cell called a globose cell.3. A rounded stem cell found in the taste buds and a progenitor of the specialized taste receptor cells.

basket cell

1. Myoepithelial cell. 2. One of the nonspiny granule cells found in the cerebral cortex.3. One of the small interneurons found in the outermost layer of the cerebellar cortex along with stellate cells.

basophilic cell

Basophil.

beta cell

1. Any of the insulin-secreting cells of the pancreas that constitute the bulk of the islets of Langerhans. Synonym: B cell 2. A basophil cell of the adenohypophysis (anterior pituitary gland).

Betz cell

See: Betz cells

bipolar cell

Bipolar neuron.

blast cell

1. A precursor cell for a specific cell type.2. An immature cell of a specific type.

blood cell

Any cell normally found circulating in the blood stream. Blood cells include red cells and white cells; red cells generally remain inside blood vessels, while white cells can also more into the tissues outside the blood vessel walls. See: blood for illus.

bone cell

An osteoblast, osteoclast, or osteocyte.

bone marrow cell

Marrow cell.

brush cell

An epithelial cell found sparsely in the lining of the bronchial tree. The cell's surface has long stiff microvilli, and the cell has the appearance of an absorptive cell.

burr cell

An erythrocyte with 10 to 30 spicules distributed over the surface of the cell, as seen in heart disease, stomach cancer, kidney disease, and dehydration. Synonym: echinocyte

cancer cell

A cell present in a neoplasm and differentiated from normal tissue cells because of its degree of anaplasia, irregularity of shape, nuclear size, changes in the structure of the nucleus and cytoplasm, increased number of mitoses, and ability to metastasize.

capsule cell

Satellite cell.

cartilage cell

Chondrocyte.

castration cell

An enlarged and vacuolated basophil cell seen in the pituitary in gonadal insufficiency or following castration.

CD3 cell

T cell.

CD4 cell

Helper T cell.

CD8 cell

A suppressor T cell, e.g., a cytotoxic T cell.

CD 34+ cell

A cell with the CD34 protein on its surface membrane. Some CD34 cells that are hemopoietic stem cells can be separated out from peripheral blood.

cementoblast cell

Cementoblast.

cementocyte cell

Any of the cells trapped within cementum that maintain cementum as a living calcified tissue by their metabolic activity.

centroacinar cell

A duct cell of the pancreas more or less invaginated into the lumen of an acinus.

chalice cell

Goblet cell.

chemoreceptor cell

Chemoreceptor.

chief cell

1. Any of the cells of the parathyroid gland that secretes the parathyroid hormone.2. Any of the cells of the gastric glands that secretes pepsinogen.

chromaffin cell

A cell that produces, stores, and secretes catecholamines (dopamine and norepinephrine). Chromaffin cells are found in the medulla of the adrenal glands and in small clusters in the sympathetic ganglia.

chromophobe cell

Chromophobe.

Clara cell

A cuboidal epithelial cell found in the lining of the terminal and the respiratory bronchioles of the lungs. Clara cells are nonciliated, and they secrete surfactant, like the type II alveolar epithelial cells found deeper in the bronchial tree.

cleavage cell

Blastomere.

clue cell

A vaginal epithelial cell, thickly coated with coccobacillary organisms. Clue cells are a hallmark of bacterial vaginosis.

columnar cell

An epithelial cell with height greater than its width.

columnar epithelial cell

Columnar cell.

cone cell

A cell in the retina whose scleral end forms a cone that serves as a light receptor. Vision in bright light, color vision, and acute vision depend on the function of the cones. See: rod cell

contrasuppressor cell

A T cell that inhibits the activity of suppressor T cells. Although a contrasuppressor cell shares this functional capability with T helper cells, it is distinguished from other CD4+ cells by its other cell surface markers and the unique group of cytokines it produces.

cortical cell

A cell in the cortex of an organ, e.g., a neuron in the cerebral cortex.

corticotroph cell

Corticotroph.

cuboid cell

A cell – usually epithelial – with a height about equal to its width and depth.

cytotoxic cell

Cytotoxic T cell.

cytotoxic T cell

A CD8+ T lymphocyte that can destroy microorganisms directly through the release of perforin and proteolytic enzymes. These cells are particularly important in the defense against viruses, rejection of allografts, and, possibly, new malignant cells. Synonym: CD8 cell; cytotoxic cel; killer T cell

D cell

An enteroendocrine cell that produces somatostatin and is found in the pancreatic islets, stomach, and small intestine. Synonym: delta cell; somatostatin cell

daughter cell

A cell formed by cell division.

decoy cell

A cell found in the urine with inclusion bodies in its nucleus. It indicates infection with BK virus in renal transplant recipients.

delta cell

Pancreatic D cell.

dendritic cell

One type of antigen-presenting cell that helps T cells respond to foreign antigens. Dendritic cells are found in epithelial tissues and include the Langerhans' cells of the skin and the interdigitating cells in lymph nodes; they also circulate in the blood.

Downey cell

See: Downey cell

dust cell

A macrophage that migrates into the lumen of lung aveoli and ingests debris, particles of air pollution, and pathogens to keep the airspaces clear.

EC cell

1. An embryonal carcinoma cell, which is a cultured cell line.2. An enterochromaffin cell that secretes substance P and is found in the stomach and small intestine.

effector cell

A cell that carries out the final response or function of a particular process. The main effector cells of the immune system, for example, are activated lymphocytes and phagocytes—the cells involved in destroying pathogens and removing them from the body. See: leukocyte

embryonic stem cell

Abbreviation: ES cell
A cell from the inner cell mass of the blastocyst (the 3-5 day old mammalian embryo) that can give rise to all the somatic cells of the body. Embryonic stem cells can be maintained as pure stem cell cultures. See: adult stem cell

endothelial cell

The type of epithelial cell that lines blood vessels and lymph vessels; these cells are usually squamous (flattened) and form sheets one layer thick. Endothelial cells are derived from mesenchyme cells of the embryo. A sheet of endothelial cells is called an endothelium. See: endothelium

enterochromaffin cell

Abbreviation: EC cell
An enteroendocrine cell that produces serotonin and is found in the small intestine. Enterochromaffin cells are very similar to the cells, found throughout the peripheral sympathetic nervous system, that are called simply 'chromaffin cells'.

enteroendocrine cell

One of the scattered hormone-producing cells found in the pancreatic islets and throughout the gastrointestinal (mainly, small intestinal) mucosa.

ependymal cell

Any of the epithelial cells that form a one-cell-thick layer lining the ventricles and the central canal of the central nervous system. The ventricular (apical) surfaces of many ependymal cells are covered with cilia or microvilli. In most places, the ependymal layer does not have a basal lamina. Specialized regions of ependymal cells include the covering of the blood vessels and loose connective tissue of the choroid plexuses; here, the ependyma is specialized to secrete cerebrospinal fluid.

epithelial cell

Any of the cells forming the cellular sheets that cover surfaces, both inside and outside the body. Epithelial cells are closely packed and take on polyhedral shapes, from tall (columnar) through squat (cuboidal) to flat (squamous). Epithelial cells adhere strongly to one another, and one of their surfaces -- the basal surface -- sticks firmly to a thin extracellular film of fibrils called a basal lamina. A sheet of epithelial cells derived from embryonic epithelia (the ectoderm or the endoderm) is called an epithelium. See: epithelium

ethmoidcell

Ethmoid sinus.

ethmoid air cell

Ethmoid sinus.

eukaryotic cell

The type of cell composing multicellular, as well as a number of unicellular, organisms. Unlike prokaryotic cells, eukaryotic cells have many of their intracellular functions organized within structures called organelles. Some organelles -- notably, the nucleus, which contains the DNA -- are enclosed by intracellular membranes.

F cell

An enteroendocrine cell that produces pancreatic polypeptide and is found in the pancreatic islets.

fat cell

Adipocyte.

flame cell

A bone marrow cell with a bright red cytoplasm, occasionally found in the marrow of patients with multiple myeloma.

flow cell

An optical cell used in photometers and cell counters, through which the sample and any standards are passed for detection and measured or counted by optical or electrometric means. See: cytometry

foam cell

A cell that contains vacuoles; a lipid-filled macrophage.

follicle cell

Follicular cell.

follicular cell

1. The secretory cell of the thyroid gland; it produces the thyroid hormones, T3 (triiodothyronine) and T4 (tetraiodothyronine or thyroxine).2. Any of the flattened somatic cells that form a monolayer around each primary oocyte in the ovary. After puberty, when an oocyte matures, during a monthly cycle, its follicular cells divide, become cuboidal, and form a multilayered coating for the oocyte; at this stage, the follicular cells are called granulosa cells.

folliculostellate cell

A supporting cell in the adenohypophysis (anterior pituitary gland); it produces bioactive peptides, including growth factors and cytokines.

foreign body giant cell

Giant cell.

G cell

An enteroendocrine cell found in the stomach that produces the hormone gastrin.

ganglion cell

1. Any neuron whose cell body is located within a ganglion.2. A neuron of the retina of the eye whose cell body lies in the ganglion cell layer. The axons of ganglion cells form the optic nerve.

germ cell

A cell whose function is to reproduce the organism. Early in development, primordial germ cells are found in the genital ridges of the embryo. Later, in the testis, the primordial germ cells are called spermatogonia, and in the ovary, they are called oogonia. When they mature, the germ cells (i.e., spermatogonia and oogonia) differentiate into haploid gametes (i.e., spermatozoa and ova). Synonym: primordial germ cell

giant cell

1. A multinucleated phagocyte created by several individual macrophages that have merged around a large pathogen or a substance resistant to destruction, such as a splinter or surgical suture. See: granuloma; tuberculosis2. A large multinucleated (40-60 nuclei) tumor cell characteristic of certain bone and tendon tumors. 3. A large multinucleated cell that invades the walls of the aorta and its major branches in giant cell arteritis.

glial cell

One of three types of nonneuronal cell in the central nervous system: astrocytes, oligodendrocytes, and microglial cells. SYN neuroglial cell Synonym: neuroglial cell

gitter cell

A macrophage present at sites of brain injury. The cells are packed with lipoid granules from phagocytosis of damaged brain cells. See: microglia

globus cell

One of the two varieties of basal cell found in the olfactory epithelium. It is a rounded neuroblast or neural stem cell for the olfactory receptor cells.

goblet cell

A mucous cell sitting between nonsecretory cells, such as is found in the intestinal epithelium.

Golgi cell

See: Golgi, Camillo

gonadotroph cell

Gonadotroph.

graft facilitating cell

Any of a group of CD8 positive, t-cell receptor negative cells that help donated bone marrow engraft in the recipient.

granule cell

1. Any of the small neurons that pack the granular cell layer of the cerebellar cortex, immediately below the Purkinje cell layer. Granule cells receive inputs (mossy fibers) from the spinal cord and brainstem (except the inferior olive). Axons of granule cells run perpendicular to the Purkinje cell dendrites, on which they synapse. 2. Any of the neurons of the cerebral cortex that are not pyramidal cells. Cortical granule cells are categorized as spiny or nonspiny. Synonym: stellate cell 3. A small axon-less neuron found in the olfactory bulb.

granulosa cell

One of the many cuboidal cells that surround and nurture the maturing oocyte. See: follicular cell (2)

gustatory cell

Taste cell.

hair cell

An epithelial cell possessing stereocilia in the maculae, cristae ampullaris, and the organ of Corti. These cells are receptors for the senses of position and hearing.

heart failure cell

A red-colored (from ingested red cells) lung macrophage often found in the sputum of patients with congestive heart failure.

HeLa cell

A line of human epithelial cells that grows well in culture. It is an immortal cancer cell that has been maintained in continuous tissue cultures for decades from a patient with carcinoma of the cervix. It is named for the first two letters of the patient's first and last names, Henrietta Lacks. HeLa cells have been used in thousands of experiments on cell growth, differentiation, and cancer, and in virology, pharmacology, and other fields.

HELMET CELLS: (Orig. mag. ×640)

helmet cell

A schistocyte or fragmented blood cell, seen in hemolytic anemias. See: illustration

helper cell

A type of T lymphocyte whose surface is marked by CD4 receptors; it is involved in both cell-mediated and antibody-mediated immune responses. It secretes cytokines that stimulate the activity of B cells and other T cells and binds with class II histocompatibility antigens, which are processed by macrophages and other antigen-presenting cells. Synonym: helper T cell See: antigen processing; T cell; cell-mediated immunity

helper T cell

Helper cell.

hematopoietic stem cell

A progenitor cell in the bone marrow that can replicate itself as well as produce precursor cells of the various blood cell lineages.

hilus cell

An androgen-producing cell found in the ovarian hilum. It is analogous to the male Leydig cell.

holly leaf cell

A cell found in blood smears of persons with sickle cell anemia.

horizontal cell

A neuron of the inner nuclear layer of the retina. The axons of these cells run horizontally and connect various parts of the retina.

Hürthle cell

See: Hürthle cell

hybridoma cell

See: hybridoma

hyperchromatic cell

A cell that contains more than the normal number of chromosomes and hence stains more densely.

I cell

An enteroendocrine cell that produces the enzyme cholecystokinin-pancreozymin (pancreaticozymin) and is found in the small intestine.

interdigitating cell

A type of antigen-presenting cell found in lymph nodes and lymphoid tissue.

interstitial cell

Any of the many cells found in connective tissue of the ovary, in the seminiferous tubules of the testes, and in the medulla and cortex of the kidney. The cells in the testes and ovaries produce hormones such as testosterone and estrogen.

intestinal absorptive cell

In the small intestine, any of the tall columnar cells topped with a brush border made of thousands of microvilli.

islet cell

A cell of the islets of Langerhans of the pancreas.

juvenile cell

The early developmental form of a leukocyte.

juxtaglomerular cell

A modified smooth muscle cell in the wall of the afferent arteriole leading to a glomerulus of the kidney. This type of cell secretes renin when blood pressure decreases to activate the renin-angiotensin mechanism, which increases sodium retention, thus elevating the blood pressure.

K cell

An enteroendocrine cell that produces gastric inhibitory peptide (glucose-dependent insulinotropic peptide) and is found in the small intestine. This peptide stimulates the beta cells of the pancreas to secrete insulin.

killer cell

Natural killer cell.

killer T cell

Cytotoxic T cell.

Kulchitsky cell

An APUD cell found in the lung.

Kupffer cell

See: Kupffer cell

L cell

An enteroendocrine cell that produces glucagon-like peptide-1 and is found in the small intestine. This peptide signals the pancreas to secrete insulin after a meal.

labile cell

A cell that is always mitotically active, such as the epithelial cells lining the stomach and the stem cells in the red bone marrow.

lactotroph cell

Lactotroph.

LAK cell

Abbreviation for lymphokine-activated killer cell. These natural killer cells, obtained from the patient's blood, have been activated in culture with interleukin-2.LAK cells; the cells can then be used to treat patients with solid malignant tumors.

Langerhanscell

A type of dendritic antigen-presenting cell that typically resides in the skin.

L.E. CELL (center): (Orig. mag. ×1000)

L.E. cell

Historically, an abbreviation for lupus erythematosus cell, a polymorphonuclear leukocyte that contains the phagocytized nucleus of another cell. It is characteristic but not diagnostic of lupus erythematosus.

This distinctive cell may form when the blood of patients with systemic lupus erythematosus is incubated and further processed according to a specified protocol. The plasma of some patients contains an antibody to the nucleoprotein of leukocytes. These altered nuclei, which are swollen, pink, and homogeneous, are ingested by phagocytes. These are the L.E. cells. The ingested material, when stained properly, is lavender and displaces the nucleus of the phagocyte to the inner surface of the cell membrane. The L.E. cell phenomenon can be demonstrated in most patients with systemic lupus erythematosus but is not essential for diagnosis.

illustration

Leydig cell

See: Leydig's cell

littoral cell

A macrophage found in the sinuses of lymphatic tissue.

liver cell

Hepatocyte.

lutein cell

A cell of the corpus luteum of the ovary that contains fatty yellowish granules. Granulose lutein cells are hypertrophied follicle cells; these lutein (paralutein) cells develop from the theca interna.

lymphoid cell

An obsolete term for lymphocyte.

lymphokine-activated killer cell

LAK cell.

M cell

1. A microfold cell, which is a cell in the gastrointestinal epithelium covering patches of lymphoid tissue. M cells transport antigens from the intestinal lumen to the underlying lymphoid tissues for recognition and processing. 2. An APUD cell that produces melanotropin and is found in the pituitary gland.

macroglial cell

An astrocyte or an oligodendrocyte.

marrow cell

Bone marrow cell.

MAST CELL

mast cell

A large tissue cell resembling a basophil, which is essential for inflammatory reactions mediated by immunoglobulin E (IgE) but does not circulate in the blood. Mast cells are present throughout the body in connective tissue, but are concentrated beneath the skin and the mucous membranes of the respiratory and digestive tracts. Mast cells are covered with IgE molecules, which bind with foreign antigens and stimulate degranulation, releasing such mediators as histamine, prostaglandins, leukotrienes, and proteinases from densely packed granules within the cytoplasm. These mediators produce type I (immediate) hypersensitivity reactions (e.g., urticaria, allergic rhinitis, asthma, angioedema, and systemic anaphylaxis). See: illustration

mastoid cell

Mastoid air cell.

mastoid air cell

Any of the variable-sized, air-filled sinuses inside the mastoid antrum. About 20% of adult skulls have no mastoid air cells.

matrix stem cell

A stem cell derived from Wharton's jelly.

memory cell

A cell derived from B or T lymphocytes that can quickly recognize a foreign antigen to which the body has been previously exposed. Memory T cells stimulate T helper lymphocytes and cytotoxic T cells; memory B cells stimulate the production of antigen-specific antibodies by B plasma cells. Both types of memory cells survive for years, providing a durable adaptive immune response against foreign antigens.

mesenchyme cell

One of the two basic somatic cell lineages -- the other being epithelial cells. In contrast to epithelial cells, mesenchyme cells are not polarized and are frequently motile. In the early embryo, mesenchyme cells fill many of the spaces enclosed by epithelia. Later, mesenchyme cells will secrete the space-filling extracellular matrix molecules, such as collagen and glycoproteins, that characterize connective tissue.

mesenchymal stem cell

A stem cell found in connective tissue and capable of producing cells of the connective tissue lineages, such as cartilage, bone, muscle, and fat cells.

mesothelial cell

The type of epithelial cell that lines serous (pleural, peritoneal, and pericardial) cavities, blood vessels, and lymph vessels; these cells are usually squamous (flattened) and form sheets one layer thick. Mesothelial cells are derived from mesenchyme cells of the embryo. A sheet of mesothelial cells is called a mesothelium. See: mesothelium

microglial cell

A small glial cell of the central nervous system and retina. Microglia have spiky branched processes and are arranged homogeneously throughout the brain and spinal cord. They are activated by disease and injury, after which they become phagocytic and sometimes resume their embryonic motility like a macrophage.

mitral cell

One of the two principal neurons of the olfactory bulb -- the other being the tufted cell. In a complex synaptic formation called a glomerulus, each of the mitral and tufted cells receives synaptic inputs from axons of the olfactory nerve. The axons of the mitral and tufted cells form the olfactory tract and synapse in the olfactory cortex.

mossy cell

An astrocyte or other glial cell with many branching processes. See: neuroglia

mother cell

A cell that gives rise to similar cells through fission or budding. Synonym: parent cell

mucosal cell

Any cell in a mucosal epithelium.

mucous cell

An epithelial cell that secretes mucus and IgA antibodies. Mucous cells and serous cells are the two varieties of secretory cells found in exocrine glands. Synonym: mucus cell

mucus cell

Mucous cell.

multinucleated giant cell

Giant cell.

multipolar cell

Multipolar neuron.

muscle cell

See: muscle

myeloid cell

Any white blood cell other than lymphocytes.

myeloma cell

A cell present in the bone marrow of patients with multiple myeloma.

myoepithelial cell

A smooth muscle cell found in some epithelia; it lies between glandular cells and the basal lamina of sweat, mammary, lacrimal, and salivary glands. Synonym: basket cell

natural killer cell

Abbreviation: NK cell
A large granular lymphocyte – a defensive cell of innate immunity – that bonds to cells and lyses them by releasing cytotoxins. Natural killer cells are null cells, lymphocytes that do not have B cell or T cell surface markers, and they can be activated without previous antigen exposure. NK cells destroy cells infected with viruses and some types of tumor cells in cultures. They also secrete gamma interferon (INF?), tumor necrosis factor alpha (TNFa), and granulocyte-macrophage colony-stimulating factor (GMCSF), enhancing the effect of T lymphocytes. Synonym: killer cell

nerve cell

Neuron.

neural crest cell

Embryonic cells of the neuron-glia lineage that form along the ridges (neural folds) of the neural plate and that migrate into the developing organism to produce a variety of tissues. The migratory ability of these embryonic epithelial cells is similar to the motility of mesenchyme cells; this has led neural crest cells to be called mesectodermal cells. In the neural lineage, neural crest cells give rise to the dorsal root ganglia, the placodes that will develop into the olfactory and auditory sensory organs, the pituitary gland, the peripheral autonomic nervous system, and the neurenteric and APUD cells. In the glial lineage, neural crest cells give rise to Schwann cells and other peripheral satellite cells. In addition, neural crest cells of the cranial region give rise to certain facial connective tissue, including the bones of the nasal cavities, the roof of the mouth, and the sella turcica.

neuroglial cell

Glial cell.

Niemann-Pick cell

See: Niemann-Pick cell

NK cell

Natural killer cell.

nonstem cell

Any cell found in the bone marrow that cannot reconstitute the marrow or give rise to more differentiated blood cells.

null cell

A large lymphocyte without the cell markers of either a T cell or a B cell. Natural killer cells are examples of null cells.

odontoblast cell

Odontoblast.

oligodendroglial cell

Oligodendrocyte.

olfactory cell

Olfactory receptor cell.

olfactory receptor cell

A cell of the olfactory mucosa that has receptors for the sense of smell. Olfactory cells are continuously replaced from stem cells throughout adult life. Synonym: olfactory cell

osteoprogenitor cell

Any of the mesenchyme precursor cells committed to the bone lineage and capable of producing osteoblasts and osteocytes. Osteoprogenitor cells are found in bone, bone marrow, and other connective tissue.

oxyntic cell

A parietal cell of the gastric glands; it produces hydrochloric acid and the intrinsic factor.

parabasal cell

An abnormal but not malignant cell seen in some cytologic specimens obtained during Papanicolaou tests (Pap tests). It is found in women with vaginal atrophy, in some postpartum women, some women suffering from anorexia or starvation, and some who have used progesterone for contraception.

parent cell

Mother cell.

phalangeal cell

One of the cells supporting the hair cells of the organ of Corti. These cells form several rows of outer phalangeal cells (Deiters' cells) and a single row of inner phalangeal cells.

phantom cell

See: red cell ghost

pigment cell

Any cell that normally contains pigment granules.

plasma cell

A cell derived from a B lymphocyte that has been sensitized to a specific foreign antigen and produces antibodies to that particular antigen. It may be found in the blood or in tissue fluid. Synonym: plasmacyte

postganglionic cell

Postganglionic neuron.

PP cell

An enteroendocrine endocrine cell found in the pancreatic islets that produces pancreatic polypeptide.

pre-B cell

The immediate precursor of a lymphocytic B cell.

preganglionic cell

Preganglionic neuron.

prickle cell

A cell with spiny processes that connect with similar processes of adjoining cells. These are found in the stratum spinosum of the keratinized epithelium of the epidermis.

primary cell

In physical therapy, a device consisting of a container, two solid conducting elements, and an electrolyte for the production of electric current by chemical energy.

primordial cell

Primordial germ cell.

primordial germ cell

A germ cell before it begins its maturation into a haploid gamete. Synonym: primordial cell

progenitor cell

A cell (sometimes a stem cell) that produces cells of a particular lineage, e.g., a neuroblast.

prokaryotic cell

The form of cell composing many primitive unicellular organisms, such as bacteria. Prokaryotic cells do not have nuclei, which are partitioned by an intracellular membrane; instead the DNA forms one main coil in the cell cytoplasm.

Purkinje cell

See: Purkinje, Johannes E. von

pus cell

A leukocyte present in pus. Pus cells are often degenerated or necrotic.

pyramidal cell

A large, common neuron found in the cerebral cortex. Pyramidal cells are flask-shaped or triangular, and, in the parts of the cortex with six layers, they occupy the fifth layer. Pyramidal cell dendrites project up into the most superficial layer of the cortex, while pyramidal cell axons run in the opposite direction, i.e., downward and out of the cortex. Synonym: pyramidal neuron

radial glial cell

A structural macroglial cell that is a key component of the developing nervous system. Radial glial cells first appear in the neural tube, where their cell bodies are suspended between two thin cell processes; the apical process attaches to the inner (ventricular) surface of the neural tube, and the basal process attaches to the outer (pial) surface. Early in development, neuroblasts migrate radially along the scaffolding formed by the radial glial cell processes, and growing axons may follow the scaffolding longitudinally. Later, many radial glial cells retract their processes and differentiate into astrocytes.

red cell

A small cell that is filled with hemoglobin, has no nucleus, and is shaped like a biconcave disc. Red cells transport oxygen to tissues and carbon dioxide to the lungs. Individual red cells have a life span of 3-4 months, and new red cells are continually being produced in the bone marrow. In a healthy person, 99% of the cells circulating in the blood are red cells. Synonym: erythrocyte; red blood cell; red blood corpuscle See: erythrocyte

red blood cell

Abbreviation: RBC
Red cell.

Renshaw cell

See: Renshaw cell

resting cell

1. A cell that is not dividing. See: interphase2. A cell not performing its normal function (i.e., a nerve cell that is not conducting an impulse or a muscle cell that is not contracting).

reticular cell

1. An undifferentiated cell of the spleen, bone marrow, or lymphatic tissue that can develop into one of several types of connective tissue cells or into a macrophage. 2. A cell of reticular connective tissue. See: reticular tissue

reticuloendothelial cell

An out-of-date term for a cell of the mononuclear phagocytic system.

Rieder cell

See: Rieder cell

rod cell

A cell in the retina of the eye whose scleral end is long and narrow, forming a rod-shaped sensory receptor. Rods are stimulated by light and are essential for vision in dim light. See: cone cell

rosette cell

A rose-shaped cluster of phagocytes surrounding lysed nuclear material or red blood cells. Rosette cells occur frequently in blood in which L.E. cells are present. Rosette cells are not diagnostic of lupus erythematosus. See: L.E. cell

Rouget cell

See: Rouget cell

S cell

An enteroendocrine cell that produces secretin and is found in the small intestine.

satellite cell

1. A stem cell associated with skeletal muscle that may form a limited number of new muscle cells after injury.2. One of the neuroglia cells enclosing the cell bodies of sensory neurons in spinal ganglia. Synonym: capsule cell

scavenger cell

A phagocyte that cleans up disintegrating tissues or cells.

Schwann cell

See: Schwann cell

segmented cell

A segmented neutrophil (i.e., one with a nucleus of two or more lobes connected by slender filaments).

selenoid cell

See: red cell ghost

sensory cell

A cell that when stimulated gives rise to nerve impulses that are conveyed to the central nervous system.

septal cell

A type II alveolar cell that secretes pulmonary surfactant; it is adjacent to a septum of the alveoli.

serous cell

An epithelial cell that secretes a watery fluid containing proteins, glycoproteins, and often antibodies (IgA, IgG, and IgM). Serous cells and mucous cells are the two varieties of secretory cells found in exocrine glands.

Sertoli cell

See: Sertoli cell

sex cell

Gamete.

SICKLED CELLS IN SICKLE CELL DISEASE

sickle cell

An abnormal erythrocyte shaped like a sickle. Synonym: drepanocyte See: anemia, sickle cellillustration

signet-ring cell

A vacuolated cell with the nucleus off center. Mucus-secreting adenocarcinomas usually contain these cells.

skeletal muscle cell

See: muscle

smooth muscle cell

See: muscle

somatic cell

Any cell that is not a germ cell.

somatic stem cell

Adult stem cell.

somatostatin cell

D cell.

spiculed red cell

Crenated red blood cells with surface projections. In most instances, this is a normal variation in red cell equilibrium and is reversible. See: acanthocyte

spider cell

Astrocyte.

squamous cell

A flat epithelial cell. Synonym: squamous epithelial cell

squamous epithelial cell

Squamous cell.

stellate cell

1. Granule cell of the cerebral cortex.2. One of the small interneurons found in the outer layer of the cerebellar cortex along with basket cells.

stellate reticuloendothelial cell

A Kupffer cell, one of the macrophages that line the sinusoids of the liver.

stem cell

An embryonic stem cell or an adult stem cell.

Sternberg-Reed cell

See: Reed-Sternberg cell

stipple cell

A red blood cell that contains small basophilic-staining dots. It is seen in lead poisoning, malaria, severe anemia, and leukemia.

striated muscle

See: muscle

suppressor T cell

A subpopulation of regulatory T lymphocytes that develop in the thymus gland, that slows or stops a specific immune response.

sustentacular cell

A supporting cell, as in the acoustic macula, organ of Corti, olfactory epithelium, taste buds, or testes.

sympathicotrophic cell

One of the large epithelial cells that occur in groups in the hilus of the ovary. They are thought to be chromaffin cells.

sympathochromaffin cell

A chromaffin cell of ectodermal origin present in the fetal adrenal gland. Sympathetic and medullary cells originate from these cells.

syncytial giant cell

Giant cell.

T cell

A lymphocyte that responds to specific antigens, with the assistance of antigen-presenting cells (APCs). T cells arise in the bone marrow and migrate to the thymus gland, where they mature; then they circulate between blood and lymph, serving as one of the primary cells of the adaptive immune response. Immature T cells are called thymocytes. Mature T cells are antigen specific. Their surface receptors (T cell receptors, abbrev. TCRs) respond only to a single antigen. T cells are further categorized using another family of surface protein markers called clusters of differentiation (CDs). All T cells have a CD3 marker. Additional markers differentiate the subclasses of T cells. CD4 T helper cells serve primarily as regulators, secreting cytokines that stimulate the activities of other white blood cells. CD8 T cells (cytotoxic T cells) directly lyse (kill) organisms, an important defense against viruses; most CD8 T cells also produce gamma interferon (INF?), one of the strongest stimulators of macrophage activity. Synonym: T lymphocyte See: immune response; lymphocyte; immunological surveillance; T-cell receptor

A T cell can only recognize the "foreignness" of antigens after they have been modified by macrophages and other antigen-presenting cells (APCs). After this, T cells dominate the adaptive immune response by mobilizing B cells and other T cells of the cell-mediated immune pathways. T cells are responsible for type IV hypersensitivity reactions, such as graft rejection, and for tumor cell recognition and destruction.

See: cytokine; cell-mediated immunity

TARGET CELLS: In hemoglobin C disease (×600)

target cell

1. . An erythrocyte with a dark rounded central area surrounded by a lightly stained clear ring, which in turn is surrounded by a dense ring of peripheral cytoplasm. It is present in certain blood disorders, such as thalassemia, and in patients who have no spleen. See: hemoglobin C disease for illus Synonym: codocyte; leptocyte2. . The cell at which a signal (e.g., hormone or nerve impulse) is aimed.illustration

tart cell

A phagocyte that has ingested the unaltered nuclei of cells. These nuclei can be observed unchanged within the phagocytes.

taste cell

Any of the neuroepithelial cells within a taste bud that are receptors for the sense of taste. Each possesses on the free surface a short gustatory hair that projects through the inner taste pore. Synonym: taste receptor cell

taste receptor cell

taste cell.

tear-drop cell

An abnormally shaped blood cell, sometimes found on blood smears of patients with bone marrow fibrosis, iron deficiency, or thalassemias. Synonym: dacrocyte

tendon cell

Any of the fibroblasts of white fibrous connective tissue of tendons arranged in parallel rows.

terminally differentiated cell

A cell sufficiently committed to a particular function that it can no longer divide, e.g. a red cell.

thymic epithelial cell

The epithelial cells that form the internal scaffolding of the thymus. These cells vary in shape and size but generally align in sheets and cords, partitioning the thymus into islands of close-packed lymphocytes in the organ's cortex. Thymic epithelial cells are not simply structural and they interact actively with adjacent lymphocytes.

thymus cell

Any cell characteristic of the thymus, including thymic epithelial cells and thymocytes (thymic lymphocytes).

thyroid cell

Any cell characteristic of the thyroid gland, but usually referring to a thyroid follicular cell.

totipotent cell

An undifferentiated embryonic cell that has the potential to develop into any type of cell.

Touton giant cell

See: Touton cell

transitional cell

The stretchable epithelial cells that compose the transitional epithelium (uroepithelium), which lines most of the urinary tract. Transitional cells are strongly interconnected. They are cuboidal when not under pressure, and they become flattened and squamous when stretched. Transitional epithelia are 4-6 cells thick, and the top transitional cells -- those on the lumenal surface -- fuse to become larger and polyploid.

trophoblast cell

One of the epithelial cells forming the surface of the spherical blastocyst stage embryo. Trophoblast cells are destined to give rise to many of the extraembryonic tissues.

tufted

See: mitral cell

Türk irritation cell

See: Türk irritation cell

Tzanck cell

See: Tzanck cell

undifferentiated cell

A cell resembling an embryonic cell in that it does not have the specific morphologic or functional characteristics of any particular adult cell type.

unipolar cell

A cell with a single cell process.

Vero cell

A lineage of cells used in cell cultures and isolated from kidney epithelial cells of the African green monkey (Cercopithecus aethiops).

visual cell

A rod cell or cone cell of the retina.

wandering cell

A rarely used term for a cell (such as a macrophage) that moves like an ameba.

white cell

Leukocyte.

white blood cell

Abbreviation: WBC
Leukocyte.illustration

cell

The structural unit of the body and of all living things, whether plant or animal. Body cells vary in size from one hundredth of a millimetre to about a tenth of a millimetre, in the case of the OVUM. They are structurally complex and are engaged in constant physical, biochemical and genetic activity. The outer cell membrane contains specialized sites for the receipt of chemical information from the external environment and other receptors for the pumping of dissolved substances into and out of the cell. The central nucleus contains the chromatin—the DNA genetic blueprint for the reproduction of the cell and for the synthesis of enzymes. Surrounding the nucleus is the cytoplasm. This contains many important structures (organelles), such as the MITOCHONDRIA (tiny bags containing enzymes needed for the metabolic processes of the cell and for the conversion of glucose and oxygen into energy) and the RIBOSOMES in which proteins are formed.

cell

the structural unit of most organisms, consisting of a microscopic mass of protoplasm bounded by a semi-permeable membrane and usually containing one nucleus (in EUKARYOTES) or chromosomal material not enclosed in a nucleus (in PROKARYOTES). In prokaryotes the cytoplasm is not differentiated into specialized organelles as it is in eukaryotes. Cell size is roughly constant in all tissues and organisms, being limited by the physical restraints of unfavourable surface area/volume ratios as size increases; however, some cells are much larger, for example egg cells, neurone cells. Some organisms consist of single cells; others of many cells of different types. In plants, fungi and bacteria there is a non-living cell-wall.

Cell

The smallest living units of the body which group together to form tissues and help the body perform specific functions.Mentioned in: Cholesterol-Reducing Drugs, Gene Therapy, Wilson Disease

cell

1. In biology, the basic, structural and functional units from which living organisms and tissues are built. A cell consists of a nucleus surrounded by all the cellular contents (cytoplasm) including various organelles (mitochondria, Golgi apparatus, lysosomes, ribosomes, etc.) and inclusions (glycogen, melanin, triglycerides, etc.) suspended in intracellular fluid (water, proteins, carbohydrates, lipids, inorganic and organic substances) all enclosed in a plasma membrane. There are many types of cells (blood cells, connective tissue cells, epithelial cells, muscle cells, nerve cells, secretory cells, etc.). Living cells are capable of reproduction (for body growth, wound healing, etc.) by mitotic activity. 2. In optics, a rim in a trial frame or in an optical instrument into which a lens can be placed.
A cell See M cell.
acinar cell A type of cell found within the body of the lacrimal gland. This cell lines the lumens of glands in a lobular pattern and produces a serous secretion.
amacrine cell Retinal cell located in the inner nuclear layer connecting ganglion cells with bipolar cells. Some have an ascending axon synapsing with receptors.
B cell See P cell.
basal cell See corneal epithelium.
binocular cell A cell in the visual cortex that responds to stimulation from both eyes. It may, however, show an ocular dominance for either eye. It responds more strongly when corresponding regions of each eye are stimulated by targets of similar size and orientation. See cortical column; hypercolumn.
bipolar cell Retinal cell located in the inner nuclear layer connecting the photoreceptors with amacrine and ganglion cells.
C cell A retinal ganglion cell with slow axonal conduction which sends information to the superior colliculus and to the centre involved in the control of pupillary diameter, rather than to the lateral geniculate body. There are very few such cells. Syn. Pγ cell; W cell (thus called in the cat).
Cajal's cell See astrocytes.
clump cell Large, pigmented round cells found in the pupillary zone of the iris stroma. They are considered to be macrophages containing mainly melanin granules. The number of these cells increases with age.
colour-opponent cell's Cells which respond by increasing response to light of some wavelengths and decreasing their response to others (usually complementary). If the light stimulus contains both sets of wavelengths the two responses tend to cancel each other. Two types of cells have been identified: red-green cells and blue-yellow cells. These cells are found mainly in the lateral geniculate bodies but also among retinal ganglion cells, and they form the blobs in the visual cortex. The responses of these cells support Hering's theory of colour vision. Syn. opponent-process cell (although this term also includes a cell that increases its response to white light and decreases its response to dark). See blobs; Hering's of colour vision theory.
complex cell A cell in the visual cortex whose receptive field consists of a large responsive area, approximately rectangular in shape, surrounded by an inhibitory region. The stimulus, which is usually a slit or a straight line, gives an optimum response if appropriately orientated but falling anywhere within the excitatory area. These cells tend to respond optimally to the movement of a specifically orientated slit. Many complex cells also respond better when the optimally orientated slit is moved in one direction rather than in the opposite direction. In general, complex cells show non-linear spatial summation properties. See visual area; hypercomplex cell; simple cell; receptive field; summation.
cone cell Photoreceptor of the retina which connects with a bipolar cell and is involved in colour vision and high visual acuity and which functions in photopic vision. The outer segment of the cell is conical in shape, except in the fovea centralis where it is rod-like. In the outer segment (i.e. the part closest to the pigment epithelium) are contained hollow discs (or lamellae), the membranes of which are joined together and are also continuous with the boundary membrane of the cone cell. The visual pigments are contained in these discs. There are three types of cones, each containing a different pigment sensitive to a different part of the light spectrum. They are referred to as long-wave-sensitive (or L-cones), medium-wave-sensitive (or M-cones) and short-wave-sensitive (or S-cones). There are about six million cones in the retina, with the greatest concentration in the macular area (Fig. C4). See cone pedicle; Stiles-Crawford effect; ellipsoid; foveola; macula; visual pigment; duplicity theory; photopic vision.
fixed cell See corneal corpuscle.
ganglion cell 1. Retinal cell that connects the bipolars and other cells in the inner plexiform layer with the lateral geniculate body. The axons of the ganglion cells constitute the optic nerve fibres. There are many types of ganglion cells. The two major types are: the magno (M or parasol) ganglion cells which project mainly to the magnocellular layers of the lateral geniculate bodies; and the parvo (P) ganglion cells which project to the parvocellular layers of the lateral geniculate bodies. Two types of P ganglion cells are noted: P1, which are midget cells and have small dendritic fields and P2, which have large dendritic fields. M and P cells comprise about 10% and 82% of the ganglion cells respectively. 2. One of a collection of nerve cell bodies found in a ganglion. See C cell; M cell; P cell; melanopsin.
glial cell's Cells found throughout the nervous system. They provide support and nutrition for neurons, as well as being involved in the operation of the brain, especially the fluid surrounding the neurons and their synapses. They are also believed to be involved in the reuptake of neurotransmitters from within the synaptic cleft. There are three types of glial cells: astrocytes; microglia; oligodendroglia. Syn. glia; neuroglia.
goblet cell Cell of the conjunctival epithelium which secretes mucin. See glands of Henle; mucin; xerophthalmia.
horizontal cell Retinal cell located in the inner nuclear layer which connects several cones and rods together.
hypercomplex cell A cell in the visual cortex that receives inputs from several simple and complex cells and therefore has an even more elaborate receptive field than a complex cell. It is most effectively stimulated by a stimulus of a specific size and of a specific orientation and which is moved in a specific direction. See complex cell; simple cell.
Langerhans' cell's Dendritic cells located mainly in the epidermis, mucous membranes and lymph nodes. They have surface receptors for immunoglobulin (Fc), complement (C3) and surface HLA-DR (Ia) antigen. Langerhans' cells are also found in the conjunctival epithelium and among the basal cells, mainly of the peripheral corneal epithelium. They have antigenic functions, stimulate T-lymphocytes, prostaglandin production and participate in cutaneous delayed hypersensitivity and corneal graft rejection. Extended wear of contact lenses tends to induce an increase of these cells. They are also found in histiocytic tumours.
M cell A retinal ganglion cell, mainly located in the periphery of the retina and which assists in movement perception. M cells tend to give transient responses to stimuli and to have non-linear spatial summation properties. This cell transmits information principally to the magno cells of the lateral geniculate bodies. Syn. A cell; Pαcell; Y cell (thus called in the cat).
magno cell See ganglion cell; lateral geniculate bodies.
midget cell See ganglion cell.
Mueller's cell Neuroglial cell in the retina with its nucleus in the inner nuclear layer and with fibres extending from the external to the internal limiting membrane. These cells support the neurons of the retina and possibly assist in their metabolism. Syn. Müller cell.
orientation-specific cell A cell that responds best to specifically orientated lines. This is the case for almost all cells in the visual cortex. Examples: complex cell; simple cell. See complex cell; simple cell; receptive field.
P cell A retinal ganglion cell, mainly located in the central region of the retina and which assists in high acuity and colour vision. P cells tend to give sustained responses to stimuli and to have linear spatial summation properties. This is the most common type of ganglion cells (about 82%). This cell transmits information principally to the parvo cells of the lateral geniculate bodies. Syn. B cell; Pβcell; X cell (thus called in the cat).
parasol cell See ganglion cell.
parvo cell See ganglion cell; lateral geniculate bodies.
rod cell Photoreceptor cell of the retina which connects with a bipolar cell. It contains rhodopsin and is involved in scotopic vision. The molecules of rhodopsin are contained in about 1000 hollow discs (double lamellae or membranes), which are isolated from each other and from the boundary membrane of the rod cell. These discs are found in the outer segment (i.e. the part closest to the pigment epithelium) of the cell. There are about 100 million rod cells throughout the retina; only a small area, the foveola, is free of rods (Fig. C4). See eccentricity; ellipsoid; foveola; rhodopsin; rod spherule; duplicity theory; scotopic vision.
Schwann cell A cell whose membrane spirals around the axon with layers of myelin in between each coil, as well as being a source of the myelin sheath. The cell provides insulation to the axon. It covers about one millimetre, so that hundreds may be needed to completely cover an axon. It also allows for an increase in the speed of the nervous impulse without an increase in axonal diameter. The gaps between the segments covered by the cells are called nodes of Ranvier. See action potential.
simple cell A cell in the visual cortex whose receptive field consists of an excitatory and an inhibitory area separated by a straight line, or by a long narrow strip of one response flanked on both sides by larger regions of the opposite response. Responses occur only to a straight line or a narrow strip orientated approximately parallel to the boundary/ies between the two areas. In general, simple cells show linear spatial summation properties. They are presumably the first cells where the nervous impulses are processed as they enter the visual cortex. See visual area; complex cell; receptive field.
squamous cell See corneal epithelium.
W cell See C cell.
wing cell See corneal epithelium.
X cell See P cell.
Y cell See M cell.

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Fig. C4 Structures of a rod and a cone cell of the retina (ELM, external limiting membrane; ONL, outer nuclear layer; OPL, outer plexiform layer)

Table C1 distinguishing features of the two principal types of ganglion cells of the retina
properties	P cell (X cell)	M cell (Y cell)
size of cell body	small	large
dendritic spread	small	medium/large
receptive field size	small	medium/large
retinal distribution	90% of these at the macula	5% of these at the macula; about 13% overall
projection	LGN parvocellular layers	LGN magnocellular layers
type of response	sustained	transient
light sensitivity	low	high
wavelength response	selective (except P cells)	non-selective
spatial sensitivity	fine target detail	large target detail
temporal sensitivity	low target velocity	high target velocity

cell

(sel) 1. Smallest unit of living structure capable of independent existence, composed of a membrane-enclosed mass of protoplasm and containing a nucleus or nucleoid; highly variable and specialized in both structure and function, although all must at some stage replicate proteins and nucleic acids, use energy, and reproduce themselves. 2. Small closed or partly closed cavity; compartment or hollow receptacle. [L. cella, a storeroom, a chamber]

Patient discussion about cell

Q. How are cancer cells similar to normal cells, and how are they different? I know that a similarity would be cells regenerate, and a difference would be cancer cells grow uncontrollably.Is there anything else?A. I learned a lot of new things from the answers. Thanks.

Q. what is difference between normal cell and a cell infected with cancer? A. Malignant cells (cancerous cells, which is the correct term, since cancer isn't transmitted from cell to cell like microbes), are immortalized cells: the life span of each cell in our body is tightly regulated according to the body's needs, so cells don't multiply endlessly and eventually undergo programmed death (called apoptosis). Cancerous cells succeed to overcome this regulation, and therefore become immortalized: either excessive multiplication or avoidance of death.
You may read more here:
http://www.mayoclinic.com/health/cancer/CA99999

Q. What tests can the doctors do to see if I have cancer cells still in me? Am using my friend user name. I had a mastectomy in October of the 3cms lump. They also removed lymph nodes from armpit. They found that 2 nodes were slightly infected and 2 blood vessels leading away were the same. My oncologist says I should start chemo for 5 months followed by 5 wks of radiotherapy. I am awaiting the results from bone, heart, lungs and blood tests. What tests can the doctors do to see if I have cancer cells still in me?A. You need to have your own self examination, which you can get guidance from doctor and all the tests which you already had and the tests which you are awaiting. Like you may have clinical examination, mammograms- which you already had, breast biopsy, ultrasonography, post biopsy pathology test, HER-2 gene test to find the speed of your tumor growth. Tests to check cancer spread – like lymph, bone, liver and lungs whose results you are waiting for.

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not have two brain cells, pennies, etc. to rub toˈgether

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The Study of Cells

Bibliography

Cell (biology)

Prokaryotic (bacterial) cells

Eukaryotic cells

Plasma membrane

Cytoskeleton

Nucleus

Endoplasmic reticulum

Golgi apparatus

Lysosomes

Mitochondria

Peroxisomes

Plant cells

cell

Cell

Cell

REFERENCES

Cell

cell

cell

cell

cell

cell

cell

cell

cell

cell

cell

cell

Structure

Cell Division

A cell

accessory cell

acidophilic cell

acinar cell

adipose cell

adult stem cell

adventitial cell

air cell

alpha cell

alveolar cell

amacrine cell

ameloblast cell

anterior horn cell

antigen-presenting cell

APUD

argentaffin cell

astroglial cell

atypical glandular cells

atypical glandular cells of undetermined significance

B cell

band cell

basal cell

basket cell

basophilic cell

beta cell