Pituitary gland

Posterior pituitary gland or neurohypophysis

The posterior pituitary or neurohypophysis functions as a "deposit" for the hypothalamic hormones ADH and oxytocin, produced by hypothalamic neurons with the relative soma located in the hypothalamus (Nucleus Supraoptic → ADH and Paraventricular → Oxytocin).

• ADH or antidiuretic hormone increases the permeability of the distal renal tubule of the nephron, making it permeable to water to reduce water loss; in addition, it vasoconstricts peripheral vessels by raising blood pressure. It is therefore secreted in response to many stimuli, especially with increasing electrolytes in the blood or a drop in blood volume or blood pressure. A deficit of ADH is responsible for the so-called diabetes insipidus.
• Oxytocin is responsible for stimulating the uterine myometrium during labor (not for the neck that is released ...). Outside of pregnancy, in men it stimulates the smooth muscle cells of the prostate and the following ductus ejaculator, while in women it favors menstruation and coitus.

The posterior lobe of the pituitary or neurohypophysis is formed by three parts: median eminence, peduncle of the infundibulum and pars nervosa. It is made up of glial cells, pituites, and long nerve fibers, whose cellular bodies - located in the hypothalamus - synthesize neurosecretions; these substances then flow into the axons that descend into the infundibulum (forming a nerve bundle called the hypothalamus-neurohypophyseal beam) until they reach the neurohypophysis, where they accumulate in terminal bulges full of granules (Hering bodies); here the hypothalamic factors are poured directly into the blood capillaries (see figure) and from here they enter the general circle.

Intermediate pituitary gland

The intermediate part of the pituitary gland, considered an integral part of the adenohypophysis (pars intermedia), produces the intermediate or melanotropic hormone (MSH), which regulates the synthesis and distribution of melanin granules in melanocytes, but only in the fetus, in children small, in the pregnant woman (nipples and linea nigra (below the navel) and in some diseases.

Pituitary and feedback mechanisms

In general, the regulation of the secretory activity of hypothalamus and pituitary gland is subject to forms of negative feedback:

1. pituitary and hypothalamic endocrine cells respond to homeostatic changes by pouring their own hormones into the circulation;

2. pituitary hormones stimulate endocrine cells of target organs;

3. the hormonal response of these last ones restores the homeostasis and eliminates the stimulus that has activated them, inhibiting the secretion of the relative hypophyseal and hypothalamic hormones. Thus a sort of physiological circuit is created, where the final product of a given metabolic pathway inhibits the first stages of the same path that generated it. We are talking about the famous negative feedback circuits that preside over our body's homeostasis. The opposite settings, those with positive feedback, are rare and limited to cases where the action must be completed quickly; for example, while remaining on the subject of pituitary, oxytocin causes the release of further oxytocin during childbirth.