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PITUITARY
The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in the small, bony cavity (sella turcica) at the base of the brain.
The pituitary gland secretes hormones regulating a wide variety of bodily activities, including trophic hormones that stimulate other endocrine glands. For a while, this led scientists to call it the master gland, but now we know that it is in fact regulated by hormones released from the hypothalamus.
The pituitary gland is physically attached to the brain by the pituitary, or hypophyseal stalk connected with the median eminence.
Sections
It is divided into two sections: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
Posterior pituitary (neurohypophysis)
Its posterior lobe is connected to a part of the brain called the hypothalamus via the infundibulum (or stalk), giving rise to the tuberoinfundibular pathway. Hormones are made in nerve cell bodies positioned in the hypothalamus, and these hormones are then transported down the nerve cell's axons to the posterior pituitary. When hypothalamic neurons fire hormones release into the capillaries of the pituitary gland.
The hormones secreted by the posterior pituitary are
Anterior pituitary (Adenohypophysis)
The anterior lobe is derived from oral ectoderm, composed of glandular epithelium it communicates with the hypothalamus via a network of capillaries.
The anterior pituitary produces and secretes:
It does this in response to releasing hormones produced by the hypothalamus. These travel to the anterior lobe by way of a special capillary system, called the hypothalamic-hypophyseal portal system. These hypothalamic signalling hormones include:
These hormones from the hypothalamus cause release of the respective hormone from the pituitary, i.e. TRH releases TSH, CRH releases ACTH, GnRH releases FSH and LH and GHRH causes the release of GH except for DA, which constantly inhibits the release of prolactin normally. There is also an interaction between the hormones from the hypothalamus, i.e. TRH induces the release of prolactin.
The control of release of hormones from the pituitary is in a negative feedback loop. Their release is inhibited by increasing levels of hormones from the target gland on which they act.
Intermediate lobe
There is also an intermediate lobe in many animals. For instance in fish it is believed to control physiological colour change. In adult humans it is just a thin layer of cells between the anterior and posterior pituitary, nearly indistinguishable from the anterior lobe. The intermediate lobe produces melanocyte-stimulating hormone (MSH), although this function is often (imprecisely) attributed to the anterior pituitary.
Functions
The pituitary gland helps control the following body processes:
See also
External links
| Diencephalon - edit |
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third ventricle, interventricular foramina, optic chiasm, subfornical organ
epithalamus: pineal body, habenula, habenular nuclei
anterior hypothalamus: anterior hypothalamic nucleus, paraventricular nucleus, preoptic area, supraoptic nucleus, suprachiasmatic nucleus
intermediate/middle/tuberal/pituitary hypothalamus: infundibulum, median eminence, arcuate nucleus, ventromedial nucleus, dorsomedial hypothalamic nucleus, tuber cinereum, pituitary gland (anterior pituitary, posterior pituitary)
posterior/lateral hypothalamus: posterior nucleus, mammillary body, lateral nucleus
subthalamus: subthalamic nucleus
thalamus: pulvinar, medial geniculate nucleus, lateral geniculate nucleus, list of thalamic nuclei
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