|Function||Thyroid stimulating hormone secretion|
| Anatomical terms of microanatomy |
Thyrotropes (also called thyrotrophs) are endocrine cells in the anterior pituitary which produce thyroid stimulating hormone (TSH) in response to thyrotropin releasing hormone (TRH). [ citation needed ]Thyrotropes consist around 5% of the anterior pituitary lobe cells.
A major organ of the endocrine system, the anterior pituitary, is the glandular, anterior lobe that together with the posterior lobe makes up the pituitary gland (hypophysis). The anterior pituitary regulates several physiological processes including stress, growth, reproduction and lactation. Proper functioning of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone levels.
Thyrotropes appear basophilic in histological preparations.
Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues, as seen down the microscope, after a histological section has been stained with a basic dye. The most common such dye is haematoxylin.
A hormone is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behavior. Hormones have diverse chemical structures, mainly of three classes: eicosanoids, steroids, and amino acid/protein derivatives. The glands that secrete hormones comprise the endocrine signaling system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell or nearby cells.
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 grams (0.018 oz) in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypophysis rests upon the hypophysial fossa of the sphenoid bone in the center of the middle cranial fossa and is surrounded by a small bony cavity covered by a dural fold. The anterior pituitary is a lobe of the gland that regulates several physiological processes. The intermediate lobe synthesizes and secretes melanocyte-stimulating hormone. The posterior pituitary is a lobe of the gland that is functionally connected to the hypothalamus by the median eminence via a small tube called the pituitary stalk.
Adrenocorticotropic hormone is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent.
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.
A gonad,sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. In the female of the species the reproductive cells are the egg cells, and in the male the reproductive cells are the sperm. The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells. Both of these gametes are haploid cells.
Thyrotropin-releasing hormone (TRH), also called thyrotropin-releasing factor (TRF) or thyroliberin, is a releasing hormone, produced by the hypothalamus, that stimulates the release of thyrotropin and prolactin from the anterior pituitary. It is a tropic, tripeptidal hormone.
The posterior pituitary is the posterior lobe of the pituitary gland which is part of the endocrine system. The posterior pituitary is not glandular as is the anterior pituitary. Instead, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary, and serve as a site for the secretion of neurohypophysial hormones directly into the blood. The hypothalamic–neurohypophyseal system is composed of the hypothalamus, posterior pituitary, and these axonal projections.
The paraventricular nucleus is a nucleus in the hypothalamus. It is a group of neurons that can be activated by physiological changes including stress. Many PVN neurons project directly to the posterior pituitary where they release oxytocin into the general circulation. While the supraoptic nucleus releases vasopressin. Both the PVN and the supraoptic nucleus do produce small amounts of the other hormone, ADH and Oxytocin respectively. Other PVN neurons control various anterior pituitary functions, while still others directly regulate appetite and autonomic functions in the brainstem and spinal cord.
Somatotropes are cells in the anterior pituitary that produce growth hormone.
A lactotropic cell is a cell in the anterior pituitary which produces prolactin in response to hormonal signals including dopamine which is inhibitory and thyrotropin-releasing hormone which is stimulatory. Other regulators include oxytocin, estrogen and progesterone.
Corticotropes are basophilic cells in the anterior pituitary that produce melanocyte-stimulating hormone, adrenocorticotropic hormone (ACTH) and lipotropin. The cells produce pro-opiomelanocortin (POMC) which undergoes cleavage to ACTH and β-lipotropin (β-LPH). These cells respond to corticotropin releasing hormone (CRH) and make up 10–20% of the cells in the anterior pituitary.
Hypopituitarism is the decreased (hypo) secretion of one or more of the eight hormones normally produced by the pituitary gland at the base of the brain. If there is decreased secretion of one specific pituitary hormone, the condition is known as selective hypopituitarism. If there is decreased secretion of most or all pituitary hormones, the term panhypopituitarism is used.
Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary gland are neuroendocrine organs.
Neuroendocrine cells are cells that receive neuronal input and, as a consequence of this input, release message molecules (hormones) to the blood. In this way they bring about an integration between the nervous system and the endocrine system, a process known as neuroendocrine integration. An example of a neuroendocrine cell is a cell of the adrenal medulla, which releases adrenaline to the blood. The adrenal medullary cells are controlled by the sympathetic division of the autonomic nervous system. These cells are modified postganglionic neurons. Autonomic nerve fibers lead directly to them from the central nervous system. The adrenal medullary hormones are kept in vesicles much in the same way neurotransmitters are kept in neuronal vesicles. Hormonal effects can last up to ten times longer than those of neurotransmitters. Sympathetic nerve fiber impulses stimulate the release of adrenal medullary hormones. In this way the sympathetic division of the autonomic nervous system and the medullary secretions function together.
Neuroendocrinology is the branch of biology which studies the interaction between the nervous system and the endocrine system, that is how the brain regulates the hormonal activity in the body. The nervous and endocrine systems often act together in a process called neuroendocrine integration, to regulate the physiological processes of the human body. Neuroendocrinology arose from the recognition that the brain, especially the hypothalamus, controls secretion of pituitary gland hormones, and has subsequently expanded to investigate numerous interconnections of the endocrine and nervous systems.
The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary. Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland. The capillaries in the portal system are fenestrated which allows a rapid exchange between the hypothalamus and the pituitary. The main hormones transported by the system include gonadotropin-releasing hormone, corticotropin-releasing hormone, growth hormone–releasing hormone, and thyrotropin-releasing hormone.
A chromophobe is a histological structure that does not stain readily, and thus appears relatively pale under the microscope.
An anterior pituitary basophil is a type of cell in the anterior pituitary which manufactures hormones.
Chromatophobe is a general term used in endocrinology to describe the cell stain type of the anterior pituitary hormone: the corticotroph cells which produce adrenocorticotropic hormone (ACTH). It is described as such, as opposed to acidophil or basophil, due to its inability to hold a stain when compared to other anterior pituitary cell types.
A Folliculostellate (FS) cell is a type of non-endocrine cell found in the anterior lobe of the pituitary gland.
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