The pituitary gland, or hypophysis, is an endocrine gland Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The main endocrine glands include the pituitary gland, pancreas, ovaries, testes, thyroid gland, and adrenal glands. The hypothalamus is a neuroendocrine organ. Other organs which are not so well known for about the size of a pea and weighing 0.5 g (0.02 oz.). It is a protrusion off the bottom of the hypothalamus The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland at the base of the brain The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the skull and close to the primary, and rests in a small, bony cavity (sella turcica The sella turcica is a saddle-shaped depression in the sphenoid bone at the base of the human skull) covered by a dural The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for keeping in the cerebrospinal fluid. The name "dura mater" is derived from fold (diaphragma sellae The diaphragma sellae or sellar diaphragm is the circular fold of dura mater that almost completely roofs the fossa hypophyseos in the sphenoid bone of the skull. It retains the pituitary gland in the fossa hypophyseos, with only the infundibulum of the pituitary gland passing through it). The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa The middle fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest at the base of the brain The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the skull and close to the primary. It is considered a master gland. The pituitary gland secretes hormones A hormone is a chemical released by a cell in one part of the body, that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. It is essentially a chemical messenger that transports a signal from one cell to another. All multicellular organisms produce hormones; regulating homeostasis Homeostasis is the property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition. Typically used to refer to a living organism, the concept came from that of milieu interieur that was created by Claude Bernard and published in 1865. Multiple dynamic equilibrium adjustment, including tropic hormones Tropic hormones are hormones produced and secreted by the anterior pituitary which target endocrine glands. Tropic hormones include: that stimulate other endocrine glands Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The main endocrine glands include the pituitary gland, pancreas, ovaries, testes, thyroid gland, and adrenal glands. The hypothalamus is a neuroendocrine organ. Other organs which are not so well known for. It is functionally connected to the hypothalamus The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland by the median eminence The median eminence is part of the inferior boundary for the hypothalamus part of the human brain. A small swelling on the tuber cinereum posterior to the infundibulum - atop the pituitary stalk - the median eminence lies in the area roughly bounded on its posterolateral region by the cerebral peduncles, and on its anterolateral region by the.

Sections

Located at the base of the brain, the pituitary is composed of two lobes: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). The pituitary is functionally linked to the hypothalamus by the pituitary stalk The pituitary stalk is the connection between the hypothalamus and the posterior pituitary, whereby hypothalamic releasing factors are released and, in turn, stimulate the release of pituitary hormones. Although the pituitary gland is known as the master endocrine gland, both of its lobes are under the control of the hypothalamus The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland.

Anterior pituitary (Adenohypophysis)

The anterior pituitary synthesizes and secretes important endocrine hormones, such as ACTH Adrenocorticotropic hormone , also known as corticotropin, is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It is an important component of the hypothalamic-pituitary-adrenal axis and is often produced in response to biological stress (along with corticotropin-releasing hormone from the hypothalamus). Its, TSH Thyroid-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland, PRL Prolactin or Luteotropic hormone (LTH) is a peptide hormone discovered by Dr. Henry Friesen, primarily associated with lactation. In breastfeeding, the act of an infant sucking the nipple stimulates the production of prolactin, which fills the breast with milk via a process called lactogenesis, in preparation for the next feed. Oxytocin, another, GH Growth hormone is a protein-based poly-peptide hormone. It stimulates growth, cell reproduction and regeneration in humans and other animals. It is a 191-amino acid, single-chain polypeptide hormone that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland. Somatotropin refers to, endorphins Endorphins are endogenous opioid peptides that function as neurotransmitters. They are produced by the pituitary gland and the hypothalamus in vertebrates during exercise, excitement, pain, consumption of spicy food and orgasm, and they resemble the opiates in their abilities to produce analgesia and a feeling of well-being, FSH Follicle-stimulating hormone is a hormone found in humans and other animals. It is synthesized and secreted by gonadotropes of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and Luteinizing hormone (LH) act synergistically in reproduction, and LH Luteinizing hormone is a hormone produced by the anterior pituitary gland. These hormones are released from the anterior pituitary under the influence of the hypothalamus The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary Capillaries are the smallest of a body's blood vessels and are part of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste chemical substances between blood and surrounding system, called the hypothalamic-hypophyseal portal system The hypophyseal portal system is the system of blood vessels that link the hypothalamus and the anterior pituitary in the brain. The anterior pituitary is divided into anatomical regions known as the pars tuberalis, pars intermedia, and pars distalis. It develops from a depression in the dorsal wall of the pharynx (stomodial part) known as Rathke's pouch The pouch eventually loses its connection with the pharynx giving rise to the anterior pituitary. The anterior wall of Rathke's pouch proliferates, filling most of the pouch to form pars distalis and pars tuberalis. The posterior wall forms pars intermedia.

Posterior pituitary (Neurohypophysis)

The posterior pituitary stores and releases:

• Oxytocin Oxytocin (sold as Pitocin, Syntocinon) is a mammalian hormone that acts primarily as a neurotransmitter in the brain. Also known as alpha-hypophamine (α–hypophamine), oxytocin has the distinction of being the very first polypeptide hormone to be sequenced and synthesized biochemically by Vincent du Vigneaud et al. in 1953, most of which is released from the paraventricular nucleus The paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin into the general circulation. Other PVN neurons in the hypothalamus The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland
• Antidiuretic hormone Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone (ADH), is a hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorbtion of molecules in the tubules of the kidneys by affecting the tissue's permeability. It plays a key role in homeostasis, and the regulation (ADH, also known as vasopressin Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone (ADH), is a hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's permeability. It also increases peripheral vascular resistance, which and AVP, arginine vasopressin), the majority of which is released from the supraoptic nucleus The supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, it contains about 3,000 neurons in the hypothalamus The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland

Oxytocin is one of the few hormones to create a positive feedback loop. For example, uterine contractions stimulate the release of oxytocin from the posterior pituitary, which, in turn, increases uterine contractions. This positive feedback loop continues throughout labor.

Intermediate lobe

There is also an intermediate lobe Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells - basophils, chromophobes, and colloid-filled cysts. The cysts are the remainder of Rathke’s pouch in many animals. For instance, in fish, it is believed to control physiological color change. In adult humans, it is just a thin layer of cells between the anterior and posterior pituitary. The intermediate lobe produces melanocyte-stimulating hormone The melanocyte-stimulating hormones are a class of peptide hormones that in nature are produced by cells in the intermediate lobe of the pituitary gland. They were first isolated by the Yale professor Aaron B. Lerner. Synthetic analogs of these naturally occurring hormones have also been developed and researched (MSH), although this function is often (imprecisely) attributed to the anterior pituitary.

Variations among vertebrates

The pituitary gland is found in all vertebrates, but its structure varies between different groups.

The division of the pituitary described above is typical of mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not, and is also true, to varying degrees, of all tetrapods Tetrapods are vertebrate animals having four feet, legs or leglike appendages. Amphibians, reptiles, dinosaurs, birds, and mammals are all tetrapods, and even the limbless snakes are tetrapods by descent. The earliest tetrapods radiated from the Sarcopterygii, or lobe-finned fish. However, only in mammals does the posterior pituitary have a compact shape. In lungfishes Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best-known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Today, they live only in Africa, it is a relatively flat sheet of tissue lying above the anterior pituitary, and in amphibians Amphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species, reptiles Reptiles are animals in the class Reptilia characterized by breathing air, a "cold-blooded" (poikilothermic) metabolism, laying tough-shelled amniotic eggs (or retaining the same membrane system in species with live birth), and skin with scales or scutes. They are tetrapods (either having four limbs or being descended from four-limbed and birds Birds are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich, it becomes increasingly well developed. The intermediate lobe is generally not well developed in tetrapods, and is entirely absent in birds.^[2]

Apart from lungfishes, the structure of the pituitary in fish is generally different from that in tetrapods. In general, the intermediate lobe tends to be well developed, and may equal the remainder of the anterior pituitary in size. The posterior lobe typically forms a sheet of tissue at the base of the pituitary stalk, and in most cases sends irregular finger-like projection into the tissue of the anterior pituitary, which lies directly beneath it. The anterior pituitary is typically divided into two regions, a more anterior rostral portion and a posterior proximal portion, but the boundary between the two is often not clearly marked. In elasmobranchs Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fishes, that includes the sharks (Selachimorpha) and the rays and skates (Batoidea) there is an additional, ventral lobe beneath the anterior pituitary proper.^[2]

The arrangement in lampreys A lamprey is a parasitic marine/aquatic animal with a toothed, funnel-like sucking mouth. Translated directly, their name means stone lickers (lambere: to lick, and petra: stone). While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority. In zoology, lampreys are, which are amongst the most primitive of all fish, may indicate how the pituitary originally evolved in ancestral vertebrates. Here, the posterior pituitary is a simple flat sheet of tissue at the base of the brain, and there is no pituitary stalk. Rathke's pouch remains open to the outside, close to the nasal openings. Closely associated with the pouch are three distinct clusters of glandular tissue, corresponding to the intermediate lobe, and the rostral and proximal portions of the anterior pituitary. These various parts are separated by meningial The meninges is the system of membranes which envelops the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system membranes, suggesting that the pituitary of other vertebrates may have formed from the fusion of a number of separate, but closely associated, glands.^[2]

Most fish also possess a urophysis, a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system. The spinal cord extends down to the space between the first and second lumbar vertebrae; it does not extend the entire length of the vertebral column. It is around 4. This may have a function in osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The.^[2]

Functions

The pituitary hormones help control some of the following body processes:

• Growth Human development is the process of growing to maturity. In biological terms, this entails growth from a one-celled zygote to an adult human being
• Blood pressure
• Some aspects of pregnancy and childbirth including stimulation of uterine contractions during childbirth
• Breast milk production
• Sex organ functions in both men and women
• Thyroid gland function
• The conversion of food into energy (metabolism)
• Water and osmolarity regulation in the body
• Secretes ADH (antidiuretic hormone) to control the absorption of water into the kidneys
• Temperature regulation

Additional images

See also

• Pituitary disease
• Head and neck anatomy
• Dantian

References

1. ^ Gibo H, Hokama M, Kyoshima K, Kobayashi S (1993). "[Arteries to the pituitary]". Nippon Rinsho 51 (10): 2550–4. PMID 8254920.
2. ^ ^{a b c d} Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 549-550. ISBN 0-03-910284-X.

External links

• NeuroNames hier-382
• Histology at BU 14201loa
• The Pituitary Gland, from the UMM Endocrinology Health Guide
• Oklahoma State, Endocrine System
• Pituitary apoplexy mimicking pituitary abscess

Categories: Glands | Endocrine system | Head and neck | Neuroendocrinology

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