Neurohypophysis: structure, functions and associated diseases.

This part of the pituitary gland plays an important role in hormonal regulation.

Our body and the organs that compose it work in tune, just like clockwork machinery, to maintain our physical health so that all the functions and activities of the organism can develop efficiently.

One of the pieces of this machinery is the neurohypophysis, a small organ of the endocrine system, which plays an essential role in regulating that has an essential role in the regulation and release of some of the most important hormones for the correct human functioning, both physical and psychological.

What is the neurohypophysis?

Within the endocrine system, formed by a large number of hormone-producing organs and structures, we find the neurohypophysis. This organ forms the posterior part of the pituitary gland.

One of the main differences between the neurohypophysis and the rest of the pituitary to which it belongs is that, due to its different embryological origin, its structure is not glandular as is the anterior pituitary. In addition, the anterior pituitary has a growth directed towards the hypothalamus, so its functions are also different.The neurohypophysis, therefore, also differs in its functions from those of the rest of the structure.

In contrast, the neurohypophysis is largely a collection of axonal projections from the hypothalamus leading to the posterior area of the anterior pituitary. The main parts into which the pituitary is divided are the median eminence, the infundibulum and the pars nervosa, which we will discuss in the next point.

As for the elements or parts that make up the mass of the neurohypophysis, it is composed of a series of cells called the infundibulum and the pars nervosa. is made up of a series of cells called pituicytes, which arewhich can be considered as glial supporting cells.

Finally, although at first glance the neurohypophysis may appear to be just another hormone-secreting gland, it is actually a kind of storehouse for substances secreted in the hypothalamus.

While it is true that the neuronal cells of the hypothalamic supraoptic and paraventricular nuclei secrete vasopressin and oxytocin, which is stored in the vesicles of the axons of the neurohypophysis of the neurohypophysis, which releases these hormones in response to electrical impulses coming from the hypothalamus.

Structure

As mentioned above, the posterior pituitary area, or neurohypophysis, consists mainly of neuronal projections of magnocellular neurosecretory cells extending from the supraoptic and paraventricular nuclei of the hypothalamus.

In the axons of these neurosecretory cells the neurohypophyseal hormones known as oxytocin and vasopressin are stored and released. These are released into the neurohypophyseal capillaries.. From there some of them enter the bloodstream circulation, while others return to the pituitary system.

Although the differentiation of the various parts of the pituitary may vary according to classifications, most sources include the following three structures:

1. Median eminence

The area of the neurohypophysis known as the median eminence is that which is attached to the infundibulum. This takes the form of a small swelling and is one of the seven areas of the brain that do not have a blood-brain barrier, which means that it is an organ with permeable capillaries. is an organ with permeable capillaries..

The main function of the median eminence is to act as a gateway for the release of hypothalamic hormones. However, it also shares continuous perivascular spaces with the adjacent hypothalamic arcuate nucleus, indicating a possible sensory role.

2. Infundibulum

The infundibulum is the connection between the hypothalamus and the posterior pituitary. It carries axons from the magnocellular neurosecretory cells of the hypothalamus to the posterior pituitary, where they release their neurohypophyseal hormones (oxytocin and vasopressin) into the blood.

3. Pars nervosa

Also known as the neural lobe or posterior lobe.This region constitutes the major part of the neurohypophysis and is the storage site of oxytocin and vasopressin. It is often considered synonymous with the neurohypophysis, but it is only part of the neurohypophysis.

Finally, some classifications also include the middle pituitary as part of the neurohypophysis, but this is not common.

Functions

Although, as mentioned at the beginning of the article, the neurohypophysis is often mistakenly considered as a hormone-producing gland, its main function is not to synthesize hormones, its main function is not to synthesize these substances, but to store and release the two classic hormones and release the two hormones classically related to this organ: oxytocin and vasopressin.

Initially, these hormones are synthesized in the hypothalamus, transported and released in the posterior pituitary. After their production, they are stored in the regrouped neurosecretory vesicles before being secreted into the neurohypophysis via the bloodstream.

Oxytocin

Oxytocin is a neuropeptide hormone which is characterized by playing an essential role in social an essential role in social bonds, sexual reproduction in both sexes, and in being of vital importance during both sexes. and in being of vital importance both during and after childbirth.

2. Vasopressin

Also known as antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin. The main functions of this peptide hormone include increasing the amount of solute-free water reabsorbed into the circulation and constriction of arterioles, which increases peripheral vascular resistance and raises Blood pressure..

In addition, it also has a possible third function related to the release of vasopressin in certain areas of the brain. This release may play an important role in social behavior, sexual motivation, interpersonal bonding, and the mother's response to stress.

What happens if it fails? Associated diseases

A lesion, degeneration or alteration in the functioning of the neurohypophysis can result in dysregulation of the secretion of the two hormones described in the previous section.

Insufficient vasopressin secretion may lead to the development of diabetes. can lead to the development of diabetes insipidusa condition in which the body loses the ability to store and concentrate urine and which causes the person to excrete up to 20 liters of dilute urine per day.

On the other hand, an increase in the amount of vasopressin released into the blood is the main cause of Syndrome of inappropriate antidiuretic hormone secretion (SIADH), a disease of the neurohypophysis mostly caused by drugs. and causes all kinds of gastrointestinal, neuromuscular, respiratory and neurological symptoms.