pineal gland

(pĭn`eəl), small organ (about the size of a pea) situated in the brainbrain,
the supervisory center of the nervous system in all vertebrates. It also serves as the site of emotions, memory, self-awareness, and thought. Anatomy and Function
..... Click the link for more information. . Long considered vestigial in humans, the structure, which is also called the pineal body or the epiphysis, is present in most vertebrates. It is sensitive to different levels of light and is essential to the functioning of an animal's biological clock. In many animals, including humans, the pineal gland synthesizes a hormone called melatonin in periods of darkness. Melatonin synthesis is halted when light hits the retina of the eye, sending impulses to the gland via the optic nerve. Besides influencing daily, or circadian, rhythms such those of as sleep and temperature, the pineal gland and melatonin appear to direct annual rhythms and seasonal changes in animals. The pineal gland and melatonin are now being studied for their roles in sleep, reproduction, aging, and seasonal affective disorderseasonal affective disorder
(SAD), recurrent fall or winter depression characterized by excessive sleeping, social withdrawal, depression, overeating, and pronounced weight gain.
..... Click the link for more information. . In humans the pineal gland begins to produce melatonin at age 3 months; production falls steadily from puberty on.

Pineal gland

An endocrine gland located in the brain which secretes melatonin, is strongly regulated by light stimuli, and is an important component of the circadian timing system. The pineal gland is virtually ubiquitous throughout the vertebrate animal kingdom. In nonmammalian vertebrates, it functions as a photoreceptive third eye and an endocrine organ. In mammals, it serves as an endocrine organ that is regulated by light entering the body via the eyes. Despite extensive species variation in anatomy and physiology, the pineal gland generally serves as an essential component of the circadian system which allows animals to internally measure time and coordinate physiological time-keeping with the external environment. See Biological clocks, Brain

The pineal gland is an unpaired organ attached by a stalk to the roof of the diencephalon. In frogs and lizards, one component of the pineal complex (the frontal organ or parietal eye) projects upward through the skull to lie under the skin; in all other vertebrates the pineal is located beneath the roof of the skull. Across evolution, cells within the pineal gland have progressed from classic photoreceptor cells in the earliest vertebrates, to rudimentary photoreceptors in birds, to classic endocrine cells in mammals. See Photoreception, Sense organ

In mammals, nerve fibers extend from a variety of sources in the brain to the pineal gland. The best studied of these neural inputs is through the retinohypothalamic tract, which extends from the eyes to the pineal gland in mammals. Originating in the retina, the majority of the retinohypothalamic fibers project to or around the bilateral suprachiasmatic nuclei in the hypothalamus. These nuclei serve as endogenous oscillators with period lengths close to 24 h. Thus, the suprachiasmatic nuclei function as pacemakers for the circadian system, which regulates daily physiological and behavioral rhythms. From the suprachiasmatic nuclei there are short projections to the paired paraventricular hypothalamic nuclei, and then long descending axons project from these nuclei to synapse on preganglionic sympathetic neurons in the upper thoracic spinal cord. These sympathetic neurons then extend out of the central nervous system to the superior cervical ganglia in the neck region. From there, postganglionic sympathetic axons reenter the cranium and ultimately innervate the pineal gland.

In mammals, information about environmental light and darkness is relayed from the eye to entrain circadian neural activity of the suprachiasmatic nuclei. In turn, the suprachiasmatic nuclei synchronize circadian rhythms in the pineal gland through its sympathetic innervation. One of the best-studied rhythms in the pineal gland is the biosynthesis of the hormone melatonin. Pinealocytes also have the necessary enzymes for converting tryptophan into a larger family of indole compounds, and numerous polypeptides have been localized in the pineal gland. The biological functions of these other pineal indole and peptide constituents are currently unknown.

In all vertebrate species studied, high levels of melatonin are produced and secreted during the night, while low levels are released during the day. The melatonin circadian rhythm is produced by the endogenous pacemaking activity of the suprachiasmatic nuclei, while the entrainment of this rhythm is coordinated by signals of light and darkness relayed from the eyes. Day length or photoperiod can influence the duration that melatonin production is elevated during the night. This represents a seasonal effect of light on the pineal gland. Specifically, in the summer when days are longer and nights are shorter, the duration of increased nocturnal melatonin secretion is shorter than during the winter when nights are longer. This effect of photoperiod length influencing the duration of nighttime melatonin rise has been documented in many species, including humans.

There is extensive species diversity in the capacity of melatonin to regulate physiology. Numerous species, ranging from insects to mammals, have yearly cycles of activity, morphology, reproduction, or development which are responsive to seasonal changes in day length (photoperiodism). Among many species that breed seasonally, melatonin has been shown to be a potent regulator of the reproductive axis in both males and females. The effects of melatonin on the regulation of circadian physiology has been elucidated in many vertebrate species, including humans. In addition, melatonin has been studied in different species for its influence on retinal physiology, sleep, body temperature regulation, immune function, and cardiovascular regulation.

Pineal Gland

or pineal body, an organ in vertebrate animals and man, situated in the brain, between the superior colliculi of the tectal lamina of the mesencephalon, and attached by a stemlike structure to the third ventricle.

The pineal gland evolved from the parietal organ of some of the higher fishes and reptiles. From the standpoint of comparative anatomy, it is regarded as the organ of vision. In cyclo-stomes, the pineal gland has preserved to some extent the structure of the eye, and it is found in reduced form under the skin of the head in tailless amphibians. It has a glandlike structure in mammals, including man. Developing during embryogenesis from a protuberance in the tectum of the diencephalon, the pineal gland consists of numerous glial and epithelial cells, or pinealocytes, which are separated by connective-tissue septa. The human pineal gland weighs between 100 and 200 mg. It is supplied with blood from the carotid arteries and is innervated by sympathetic nerve fibers from the superior cervical ganglia.

The physiology of the pineal gland has been insufficiently studied, mainly because of the gland’s small size, its location, and its numerous functional connections with various organs, such as the diencephalon and the endocrine glands. In cyclostomes the pineal gland is a photoreceptor. The endocrine nature of the gland’s function has not been definitely established. As its activity diminishes with age, the gland turns into a rudimentary organ containing mineral deposits (carbonates, phosphates, calcium, and magnesium)—the “brain sand” that can be seen in roentgenograms.

Removal of the pineal gland results in premature sexual development in chicks and stimulates sexual activity in mammals. Injecting animals with pineal gland extracts causes a reduction in the weight of the gonads, hinders the development of sex characters, and inhibits spermatogenesis. The pineal gland becomes more active in castrated animals, whereas its function is inhibited by the injection of estrogens. The gland contains an anti-gonadotropic substance that inhibits the action of the gonadotropic hormones of the pituitary gland. The most pronounced effect of hypofunction of the pineal gland in man (Pellizzi’s syndrome) is premature development of the sex organs and secondary sex characters, while the gland’s hyperfunction is marked by underdevelopment of the sex glands and secondary sex characters.

REFERENCES

Kakhana, M. S. Patofiziologiia endokrinnoi sistemy. Moscow, 1968.
Khelimskii, A. M. Epifiz (shishkovidnaia zheleza). Moscow, 1969.
Chazov, E. I., and V. A. Isachenkov. Epifiz: mesto i rol’ v sisteme neiroendokrinnoi reguliatsii. Moscow, 1974.

V. M. SAMSONOVA

pineal gland

, body a pea-sized organ in the brain, situated beneath the posterior part of the corpus callosum, that secretes melatonin into the bloodstream

pineal gland

gland

[gland] an aggregation of cells specialized to secrete or excrete materials not related to their ordinary metabolic needs. Glands are divided into two main groups, endocrine and exocrine. adj., adj glan´dular.
The endocrine glands, or ductless glands, discharge their secretions (hormones) directly into the blood; they include the adrenal, pituitary, thyroid, and parathyroid glands, the islands of Langerhans in the pancreas, the gonads, the thymus, and the pineal body. The glands" >exocrine glands discharge through ducts opening on an external or internal surface of the body; they include the salivary, sebaceous, and sweat glands, the liver, the gastric glands, the pancreas, the intestinal, mammary, and lacrimal glands, and the prostate. The lymph nodes" >lymph nodes are sometimes called lymph glands but are not glands in the usual sense.

Classification of glands according to mode of secretion. From Applegate, 2000.acinous gland one made up of one or more acini" >acini (oval or spherical sacs).adrenal gland see adrenal gland.apocrine gland one whose discharged secretion contains part of the secreting cells.areolar g's Montgomery's glands.axillary g's lymph nodes in the axilla.Bartholin g's two small mucus-secreting glands, one on each side in the lower pole of the labium majus and connected to the surface by a duct lined with transitional cells, which opens just external to the hymenal ring. Their exact function is not clear but they are believed to secrete mucus to moisten the vestibule during sexual excitement. Called also major vestibular glands.Bowman's g's olfactory glands.bronchial g's seromucous glands in the mucosa and submucosa of the bronchial walls.Brunner's g's glands in the submucosa of the duodenum that secrete intestinal juice; called also duodenal glands.buccal g's seromucous glands on the inner surface of the cheeks; called also genal glands.bulbocavernous g's (bulbourethral g's) two glands embedded in the substance of the sphincter of the male urethra, posterior to the membranous part of the urethra; their secretion lubricates the urethra; called also Cowper's glands.cardiac g's mucus-secreting glands of the cardiac part (cardia) of the stomach.celiac g's lymph nodes anterior to the abdominal aorta.ceruminous g's cerumin-secreting glands in the skin of the external auditory canal.cervical g's 1. the lymph nodes of the neck.2. compound clefts in the wall of the uterine cervix.ciliary g's sweat glands that have become arrested in their development, situated at the edges of the eyelids; called also Moll's glands.circumanal g's specialized sweat and sebaceous glands around the anus; called also Gay's glands.Cobelli's g's mucous glands in the esophageal mucosa just above the cardia.coccygeal gland glomus coccygeum.compound gland one made up of a number of smaller units whose excretory ducts combine to form ducts of progressively higher order.Cowper's g's bulbourethral glands.ductless g's endocrine glands.duodenal g's Brunner's glands.Ebner's g's serous glands at the back of the tongue near the taste buds.eccrine gland one of the ordinary or simple sweat glands, which are of the merocrine type.endocrine g's see endocrine glands.exocrine g's glands that discharge their secretions through ducts opening on internal or external surfaces of the body; see gland" >gland.fundic g's (fundus g's) numerous tubular glands in the mucosa of the fundus and body of the stomach that contain the cells that produce acid and pepsin.gastric g's the secreting glands of the stomach, including the fundic, cardiac, and pyloric glands.Gay's g's circumanal glands.genal g's buccal glands.glossopalatine g's mucous glands at the posterior end of the smaller sublingual glands.haversian g's synovial villi.holocrine gland one whose discharged secretion contains the entire secreting cells.intestinal g's straight tubular glands in the mucous membrane of the intestines, in the small intestine opening between the bases of the villi, and containing argentaffin cells. Called also crypts or glands of Lieberkühn.jugular gland a lymph node behind the clavicular insertion of the sternocleidomastoid muscle.Krause's gland an accessory lacrimal gland deep in the conjunctival connective tissue, mainly near the upper fornix.lacrimal g's the glands that secrete tears; see also lacrimal apparatus.g's of Lieberkühn intestinal glands.lingual g's the seromucous glands on the surface of the tongue.lingual g's, anterior seromucous glands near the apex of the tongue.Littre's g's 1. preputial glands.2. the male urethral glands.lymph gland lymph node.major vestibular g's Bartholin glands.mammary gland a specialized gland of the skin of female mammals, which secretes milk for the nourishment of their young; it exists in a rudimentary state in the male. See also breast.meibomian g's sebaceous follicles between the cartilage and conjunctiva of the eyelids. Called also tarsal glands.merocrine gland one whose discharged secretion contains no part of the secreting cells.mixed g's 1. seromucous glands.2. glands that have both exocrine and endocrine portions.Moll's g's ciliary glands.Montgomery's g's sebaceous glands in the mammary areola; called also areolar glands.mucous g's glands that secrete mucus.olfactory g's small mucous glands in the olfactory mucosa; called also Bowman's glands.parathyroid g's see parathyroid glands.parotid g's see parotid glands.peptic g's gastric glands that secrete pepsin.pineal gland pineal body.pituitary gland see pituitary gland.preputial g's small sebaceous glands of the corona of the penis and the inner surface of the prepuce, which secrete smegma; called also Littre's glands and Tyson's glands.prostate gland prostate.pyloric g's the mucin-secreting glands of the pyloric part of the stomach.salivary g's see salivary glands.sebaceous gland a type of holocrine gland of the corium that secretes an oily material (sebum) into the hair follicles.

Glands: The relationship of the hair follicle, eccrine and apocrine sweat glands and sebaceous glands. From Copstead, 1995.sentinel gland an enlarged lymph node, considered to be pathognomonic of some pathologic condition elsewhere.seromucous g's glands that are both serous and mucous.serous gland a gland that secretes a watery albuminous material, commonly but not always containing enzymes.sex gland (sexual gland) gonad.simple gland one with a nonbranching duct.Skene's g's the largest of the female urethral glands, which open into the urethral orifice; they are regarded as homologous with the prostate. Called also paraurethral ducts.solitary g's solitary follicles.sublingual gland a salivary gland on either side under the tongue.submandibular gland (submaxillary gland) a salivary gland on the inner side of each ramus of the mandible.sudoriferous gland (sudoriparous gland) sweat gland.suprarenal gland adrenal gland.sweat gland see sweat gland.target gland any gland affected by a secretion or other stimulus from another gland, such as those affected by the secretions of the pituitary gland.tarsal g's meibomian glands.thymus gland thymus.thyroid gland see thyroid gland.tubular gland any gland made up of or containing a tubule or tubules.Tyson's g's preputial glands.unicellular gland a single cell that functions as a gland, e.g., a goblet cell.urethral g's mucous glands in the wall of the urethra; in the male, called also Littre's glands.uterine g's simple tubular glands found throughout the thickness and extent of the endometrium; they become enlarged during the premenstrual period.vesical g's mucous glands sometimes found in the wall of the urinary bladder, especially in the area of the trigone.vulvovaginal g's Bartholin's glands.Waldeyer's g's glands in the attached edge of the eyelid.Weber's g's the tubular mucous glands of the tongue.

pin·e·al bod·y

[TA] a small, unpaired, flattened body, shaped somewhat like a pinecone, attached at its anterior pole to the region of the posterior and habenular commissures and lying in the depression between the two superior colliculi below the splenium of the corpus callosum; it is a glandular structure, composed of follicles containing epithelioid cells and lime concretions called brain sand; despite its attachment to the brain, it appears to receive nerve fibers exclusively from the peripheral autonomic nervous system. It produces melatonin and serotonin. Synonym(s): corpus pineale [TA], glandula pinealis [TA], pineal gland [TA], conarium, epiphysis cerebri, pinus

pineal gland

n. A small, cone-shaped organ in the brain of most vertebrates that secretes the hormone melatonin. Also called epiphysis, pineal body, pineal organ.

pin·e·al gland

(pin'ē-ăl gland) [TA] A small, unpaired, flattened body shaped something like a pinecone; attached at its anterior pole to the region of the posterior and habenular commissures, and lying in the depression between the two superior colliculi below the splenium of the corpus callosum. It is a glandular structure, composed of follicles containing epitheloid cells and lime concentrations called 'brain sand'; despite its attachment to the brain, it appears to receive nerve fibers exclusively from the peripheral autonomic nervous system. It produces melanin.
Synonym(s): corpus pineale [TA] , pineal body.

pineal gland

A tiny, cone-shaped structure within the brain, whose sole function appears to be the secretion of the hormone melatonin. The amount of hormone secreted varies over a 24-hour cycle, being greatest at night. Control over this secretion is possibly exerted through nerve pathways from the retina in the eye; a high light level seems to inhibit secretion. The exact function of melatonin is not understood, but it may help to synchronize circadian (24-hour) or other biorhythms. The pineal gland is situated deep within the brain, just below the back part of the corpus callosum (the band of nerve fibres that connects the two halves of the cerebrum). In rare cases, it is the site of a tumour.

pineal gland

see PINEAL BODY.

pineal gland

pineal gland

pineal gland

pineal body

pin′eal gland`

pin·e·al gland

pineal gland

pineal gland

pineal gland

Pineal gland

Pineal Gland

REFERENCES

pineal gland

pineal gland

gland

pin·e·al bod·y

pineal gland

pin·e·al gland

pineal gland

pineal gland

pineal gland

Synonyms for pineal gland

noun a small endocrine gland in the brain

Synonyms

Related Words