embryo

(ĕm`brēō), name for the developing young of an animal or plant. In its widest definition, the embryo is the young from the moment of fertilizationfertilization,
in biology, process in the reproduction of both plants and animals, involving the union of two unlike sex cells (gametes), the sperm and the ovum, followed by the joining of their nuclei.
..... Click the link for more information. until it has become structurally complete and able to survive as a separate organism. Embryology, the scientific study of embryonic development, deals with the period from fertilization until the hatching or birth of an animal or the germinationgermination,
in a seed, process by which the plant embryo within the seed resumes growth after a period of dormancy and the seedling emerges. The length of dormancy varies; the seed of some plants (e.g.
..... Click the link for more information. of a plant. However, since the young animal may undergo metamorphosis or may remain wholly dependent on the mother for some time after birth, and since the seedling derives nourishment from food stored in its fleshy cotyledons even after it has sprouted, the exact limit of the time during which an organism is an embryo has not generally been well defined.

Modern embryology, using the techniques of molecular biology, genetics, and other disciplines, has focused on the question of what makes the embryo differentiate (see differentiationdifferentiation,
in biology, series of changes that occur in cells and tissues during development, resulting in their specialization. This, in turn, permits a greater variety of organisms.
..... Click the link for more information. ), what genetically directed molecular signals tell a single cell to divide and follow the specific pattern of growth and specialization that results in a complex multicellular organism with species-specific and individual characteristics.

Karl Ernst von BaerBaer, Karl Ernst von,
1792–1876, Estonian biologist. He was a professor at Würzburg and Königsberg and from 1834 at St. Petersburg. Considered a founder of modern embryology, he discovered the notochord as well as the mammalian ovum.
..... Click the link for more information. , who developed the biogenetic lawbiogenetic law,
in biology, a law stating that the earlier stages of embryos of species advanced in the evolutionary process, such as humans, resemble the embryos of ancestral species, such as fish.
..... Click the link for more information. , is generally regarded as the founder of embryology. E. H. Haeckel'sHaeckel, Ernst Heinrich
, 1834–1919, German biologist and philosopher. He taught (1862–1909) at the Univ. of Jena. An early exponent of Darwinism in Germany, he evolved a mechanistic form of monism based on his interpretation of Darwin's theories and set forth in his
..... Click the link for more information. "ontogeny recapitulates phylogeny" gave weight to the theory of evolution (see recapitulationrecapitulation,
theory, stated as the biogenetic law by E. H. Haeckel, that the embryological development of the individual repeats the stages in the evolutionary development of the species.
..... Click the link for more information. ). Other researchers in the field of embryology have included C. F. WolffWolff, Caspar Friedrich
, 1733–94, German biologist, a founder of observational embryology. In his Theoria generationis (1759) he reintroduced the theory of epigenesis to replace the then current theory of preformation, directing attention to the evidence of
..... Click the link for more information. , M. 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 T. 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. , developers of the cell theory; F. M. BalfourBalfour, Francis Maitland,
1851–82, Scottish embryologist; brother of A. J. Balfour. He was an early exponent of recapitulation. His Treatise on Comparative Embryology (2 vol., 1880–81) is a classic treatment of the evolution of the egg and embryo.
..... Click the link for more information. ; H. SpemannSpemann, Hans
, 1869–1941, German embryologist. He was professor of zoology (1919–35) at the Univ. of Freiburg. By transplanting embryonic tissue to a new location or to another embryo, he investigated the agency that governs the growth and differentiation of cells.
..... Click the link for more information. ; O. HertwigHertwig, Oscar
, 1849–1922, German embryologist. He studied medicine with Haeckel and Gegenbaur. In 1875 he established the fact that fertilization consists of the union of the nuclei of a male and a female sex cell.
..... Click the link for more information. ; F. R. LillieLillie, Frank Rattray,
1870–1947, American zoologist and educator, b. Toronto, B.A. Univ. of Toronto, 1891, Ph.D. Univ. of Chicago, 1894. He taught, conducted research, and was an administrator at the Univ. of Chicago from 1900.
..... Click the link for more information. ; and R. Levi-MontalciniLevi-Montalcini, Rita
, 1909–2012, Italian-American neurologist, b. Turin, Italy, M.D. Univ. of Turin, 1936. A dual citizen of Italy and the United States, Levi-Montalcini did her most important work with Stanley Cohen at Washington Univ.
..... Click the link for more information. .

Developmental Stages

Among humans, the developing young is known as an embryo until eight weeks following conception, after which time it is described, until birth, as a fetusfetus,
term used to describe the unborn offspring in the uterus of vertebrate animals after the embryonic stage (see embryo). In humans, the fetal stage begins seven to eight weeks after fertilization of the egg, when the embryo assumes the basic shape of the newborn and all the
..... Click the link for more information. . In organisms that reproduce sexually, the union of the spermsperm
or spermatozoon
, in biology, the male gamete (sex cell), corresponding to the female ovum in organisms that reproduce sexually. In higher animals the sperm is produced in the testis of the male; it is much smaller than the ovum and consists primarily of a head,
..... Click the link for more information. with the ovumovum
, in biology, specialized plant or animal sex cell, also called the egg, or egg cell. It is the female sex cell, or female gamete; the male gamete is the sperm. The study of the ovum is included in the science of embryology.
..... Click the link for more information. results in a zygote, or fertilized egg, which begins a rapid series of cell divisions called cleavage, or segmentation (see mitosismitosis
, process of nuclear division in a living cell by which the carriers of hereditary information, or the chromosomes, are exactly replicated and the two copies distributed to identical daughter nuclei.
..... Click the link for more information. ). Each kind of organism has its own characteristic sequence of development, and related species usually have similar developmental patterns.

In a typical animal, cleavage proceeds in the following pattern. Early divisions produce a hollow ball one cell thick, called a blastula, which encloses the blastocoel, or cleavage cavity. The cells divide more rapidly in the area where the nucleus of the ovum was located; this results in an invagination (inpushing) of these cells to form a ball two cells thick (the gastrula). The new cavity thus formed is the gastrocoel, also known as the primitive gut or archenteron, and its opening is the blastopore. The outer layer of cells is called the ectodermectoderm,
layer of cells that covers the surface of an animal embryo after the process of gastrulation has occurred. This outer layer, together with the endoderm, or inner layer, is present in all early embryos.
..... Click the link for more information. , the inner layer the endodermendoderm
, in biology, inner layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball.
..... Click the link for more information. . Among the coelenterates (e.g., sponges and jellyfish), these two layers become the chief functional tissues of the adult.

In higher forms of life, a third layer of cells, the mesodermmesoderm,
in biology, middle layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball.
..... Click the link for more information. , develops from one or both of the first two layers and fills the blastocoel, and invagination forms a digestive tract with only a single opening at this early stage. The flatworms (e.g., the tapeworm and the fluke) stop developing at this time. In most organisms, however, a later invagination of the ectoderm results in a gut that is open at both ends. The mesoderm then divides into two layers, the space between them being called the coelomcoelom
, fluid-filled body cavity, found in animals, which is lined by cells derived from mesoderm tissue in the embryo, and which provides for free, lubricated motion of the viscera.
..... Click the link for more information. , or body cavity. The embryo now roughly resembles a tube within a tube.

From the three primary germ layers, the organs and tissues develop. In general the ectoderm gives rise to the skin, or integument, the skin appendages (e.g., scales, feathers, hair, and nails), and the nervous system. The endoderm forms the digestive glands, as well as the lining of the alimentary tract and lungs. From the mesoderm develop the major internal organs: the skeletal, muscular, and connective tissue and the circulatory, excretory, and reproductive systems. Sense organs and endocrine glands arise from combinations of all three layers.

Nourishment of the Embryo

In lower animals, which lay their eggs in water, the developing embryo is nourished by yolk, absorbing oxygen from and discharging wastes directly into the water. In terrestrial oviparous forms, the egg contains the yolk and also a surrounding fluid (e.g., the albumen of bird eggs). In mammals, accessory membranes, comprising both embryonic and uterine tissue, develop around the embryo—the amnion, filled with liquid, and the chorion and allantois, which help to form the placenta, through which nourishment and oxygen in the blood of the mother diffuse into the fetus and wastes diffuse back. In the higher plants, the divisions of the fertilized ovum and the differentiation of the tissues to form the embryonic root (hypocotyl), stem (epicotyl), and leaves (cotyledonscotyledon
, in botany, a leaf of the embryo of a seed. The embryos of flowering plants, or angiosperms, usually have either one cotyledon (the monocots) or two (the dicots). Seeds of gymnosperms, such as pines, may have numerous cotyledons.
..... Click the link for more information. ) occur inside the ovule within the ovary at the base of the pistil. The matured ovule is the seedseed,
fertilized and ripened ovule, consisting of the plant embryo, varying amounts of stored food material, and a protective outer seed coat. Seeds are frequently confused with the fruit enclosing them in flowering plants, especially in grains and nuts.
..... Click the link for more information. ; the fruitfruit,
matured ovary of the pistil of a flower, containing the seed. After the egg nucleus, or ovum, has been fertilized (see fertilization) and the embryo plantlet begins to form, the surrounding ovule (see pistil) develops into a seed and the ovary wall (pericarp) around the
..... Click the link for more information. , when it is produced, is the developed ovary.

What does it mean when you dream about an embryo?

An embryo can represent the most vulnerable part of ourselves, the “inner child.” (Also see Baby, Miscarriage, Pregnant.)

embryo

[′em·brē·ō] (botany) The young sporophyte of a seed plant. (embryology) An early stage of development in multicellular organisms. The product of conception up to the third month of human pregnancy.

embryo

1. an animal in the early stages of development following cleavage of the zygote and ending at birth or hatching 2. a plant in the early stages of development: in higher plants, the plumule, cotyledons, and radicle within the seed

Embryo

embryo

[em´bre-o] a new organism in the earliest stage of development. In humans this is defined as the developing organism from the fourth day after fertilization" >fertilization to the end of the eighth week. After that the unborn baby is usually referred to as the fetus" >fetus. adj., adj em´bryonal, embryon´ic.
Immediately after fertilization takes place, cell division begins and progresses at a rapid rate. At approximately 4 weeks the cell mass becomes a recognizable embryo from 7 to 10 mm long with rudimentary organs. The beginnings of the eyes, ears, and extremities can be seen. By the end of the second month the embryo has grown to a length of 2 to 2.5 cm, and the head is the most prominent part because of the rapid development of the brain; the sex can be distinguished at this stage.
At the time of fertilization the ovum contains the potential beginnings of a human being. As cell division takes place the cells of the blastoderm" >blastoderm (embryonic disk) gradually form three layers from which all the body structures develop. The ectoderm" >ectoderm (outer layer) gives rise to the epidermis of the skin and its appendages, and to the nervous system. The mesoderm" >mesoderm (middle layer) develops into muscle, connective tissue, the circulatory organs, circulating lymph and blood cells, endothelial tissues within the closed vessels and cavities, and the epithelium portion of the urogenital system. From the endoderm" >endoderm (internal layer) are derived those portions not arising from the ectoderm, the liver, the pancreas, and the lungs.

Embryonic development from 3 weeks through the eighth week after fertilization. CRL is crown-to-rump length. From McKinney et al., 2000.

em·bry·o

(em'brē-ō), 1. An organism in the early stages of development. 2. In humans, the developing organism from conception until the end of the eighth month; developmental stages from this time to birth are commonly designated as fetal. 3. A primordial plant within a seed. [G. embryon, fr. en, in, + bryō, to be full, swell]

embryo

(ĕm′brē-ō′)n. pl. embry·os 1. a. The collection of cells that has developed from the fertilized egg of a vertebrate animal, before all the major organs have developed.b. A collection of such cells of a human, especially from implantation in the uterine wall through the eighth week of development.2. Botany The young sporophytic plant contained within a seed or an archegonium.3. An organism at any time before full development, birth, or hatching.4. A rudimentary or beginning stage: an idea that was the embryo of a short story.

embryo

An early stages of a developing organism, which follows fertilization of an egg including implantation and very early pregnancy–ie, from conception to the 8^th wk of pregnancy. See Preembryo. Cf Fetus.

em·bry·o

(em'brē-ō) 1. An organism in the early stages of development. 2. In humans, the developing organism from conception until the end of the eighth week; developmental stages from this time to birth are commonly designated as fetal. 3. A primordial plant within a seed. [G. embryon, fr. en, in, + bryō, to be full, swell]

embryo

(em′brē-ō″) [Gr. embryon, growing inside] 1. The young of any organism in an early stage of development.

STAGES OF DEVELOPMENT OF HUMAN EMBRYO INCLUDING MATURE FETUS

STAGES OF DEVELOPMENT OF HUMAN EMBRYO INCLUDING MATURE FETUS2. In mammals, the stage of prenatal development between fertilized ovum and fetus. See: tableillustration

Development

First week after fertilization: The zygote begins a series of mitotic divisions called cleavage and forms a morula, a solid sphere of cells. The morula develops into a blastocyst, which has an outer trophoblast and an inner cell mass. The trophoblast gives rise to the chorion, and after implantation in the uterus, becomes the fetal placenta. Second week: The amniotic cavity and yolk sac form within the inner cell mass; they are separated by the embryonic disk, which at this time consists of ectoderm and endoderm. Third week: Mesoderm develops between ectoderm and endoderm; all three germ layers are established.

The epithelium of the alimentary canal, liver, pancreas, and lungs develops from endoderm. Muscle, all connective tissues, blood, lymphatic tissue, and the epithelium of blood vessels, body cavities, kidneys, gonads, and suprarenal cortex develop from mesoderm. The epidermis, nervous tissue, hypophysis, and the epithelium of the nasal cavity, mouth, salivary glands, bladder, and urethra develop from ectoderm.

Embryo (Third through eighth weeks): The embryo increases in length from about 1.5 mm to 23 mm. The organ systems develop and the embryo begins to show human form. During this period of organogenesis, the embryo is particularly sensitive to the effects of viral infections of the mother, e.g., rubella, and toxic chemicals, including alcohol and tobacco smoke, and is sensitive to hypoxemia.

Ectoderm	Mesoderm	Endoderm
Nervous tissue	Bone, cartilage, and other connective tissues	Epithelium of respiratory tract except nose; digestive tract except mouth and anal canal; bladder except trigone
Sense organs	Male and female reproductive tracts	Proximal portion of male urethra
Epidermis, nails, and hair follicles	Heart, blood vessels, and lymphatics	Female urethra
Epithelium of external and internal ear, nasal cavity and sinuses, mouth, anal canal	Kidneys, ureters, trigone of bladder	Liver
Distal portion of male urethra	Pleura, peritoneum, and pericardium	Pancreas
	Skeletal muscle

embryo

An organism in its earliest stages of development, especially before it has reached a stage at which it can be distinguished from other species. The human embryo is so called up to the eighth week after fertilization. After that it is called a fetus.

embryo

(in animals), the stage immediately after the beginning of CLEAVAGE up to the time when the developing animal hatches, or breaks out of egg membranes, or in higher animals, is born. In humans the developing embryo is called a FOETUS after eight weeks of gestation.
(in plants), the partly developed SPOROPHYTE, which in ANGIOSPERMS is protected within a seed. At one end of the embryo axis is the RADICLE or ROOT, and at the other the apical MERISTEM, or PLUMULE in some forms, and one or two young leaves (COTYLEDONS).

Embryo

In humans, the developing individual from the time of implantation to about the end of the second month after conception. From the third month to the point of delivery, the individual is called a fetus.Mentioned in: Birth Defects, Childbirth, Echinococcosis, Ectopic Pregnancy, Gene Therapy, Human Chorionic Gonadotropin Pregnancy Test, Hypogonadism, Infertility, Miscarriage, Pregnancy, Puberty, Stem Cell Transplantation

em·bry·o

(em'brē-ō) In humans, developing organism from conception until end of the eighth week; developmental stages from this time to birth are commonly designated as fetal. [G. embryon, fr. en, in, + bryō, to be full, swell]

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Nourishment of the Embryo

What does it mean when you dream about an embryo?

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Synonyms for embryo

noun foetus

Synonyms

noun germ

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Synonyms for embryo

noun a source of further growth and development

Synonyms

Synonyms for embryo

noun (botany) a minute rudimentary plant contained within a seed or an archegonium

Related Words

noun an animal organism in the early stages of growth and differentiation that in higher forms merge into fetal stages but in lower forms terminate in commencement of larval life

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Related Words