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The principal subdivision of the thalamus into nucleus groups is the trisection of each thalamus (left and right) by a Y-shaped internal medullary lamina. This trisection divides each thalamus into anterior, medial and lateral groups of nuclei. [8] The medial group is subdivided into the medial dorsal nucleus and midline group.
These hypophysiotropic hormones are stimulated by parvocellular neurosecretory cells located in the periventricular area of the hypothalamus. After their release into the capillaries of the third ventricle, the hypophysiotropic hormones travel through what is known as the hypothalamo-pituitary portal circulation.
These hormones are released from the anterior pituitary under the influence of the hypothalamus. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary system, called the hypothalamic-hypophysial portal system. There is also a non-endocrine cell population called folliculostellate cells.
The magnocellular cells in the PVN elaborate and secrete two peptide hormones: oxytocin and vasopressin. These hormones are packaged into large vesicles, which are then transported down the unmyelinated axons of the cells and released from neurosecretory nerve terminals residing in the posterior pituitary gland. [citation needed]
The thyroid secretes thyroxine, the pituitary secretes growth hormone, the pineal secretes melatonin, the testis secretes testosterone, and the ovaries secrete estrogen and progesterone. [2] Glands that signal each other in sequence are often referred to as an axis, such as the hypothalamic–pituitary–adrenal axis.
In posterior pituitary we have hormones that control absorption of water and oxytocin. Anterior hypophysis, neurosecretory cells which release hormones. There is a pituitary portal system, with which the hormones are transported. These hormones are prolactin, growth hormone, TSH, adrenocorticotropic hormone, FSH and LH.
The pituitary gland secretes thyrotropin (TSH; Thyroid Stimulating Hormone) that stimulates the thyroid to secrete thyroxine (T4) and, to a lesser degree, triiodothyronine (T3). The major portion of T3, however, is produced in peripheral organs, e.g. liver, adipose tissue, glia and skeletal muscle by deiodination from circulating T4.
Damage to the pituitary stalk blocks the release of antidiuretic hormone, resulting in polydipsia (excessive water intake) and polyuria (excessive urination, central diabetes insipidus). The diameter of the pituitary stalk at the level of optic chiasm is 3.3 mm, and at the pituitary gland insertion site is measured at 1.9 mm. [3]