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 as a clockwork machine would, to maintain our physical health and that all the functions and activities of the body can develop effectively.
One of the pieces of this machinery is the neurohypophysis, a small organ of the endocrine system that plays an essential role in the regulation and release of some of the most important hormones for proper human functioning, both physical and psychological.
What is the neurohypophysis?
Within the endocrine system, made up of a large number of hormone-producing organs and structures, we find the neurohypophysis. This organ makes up the back 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 the anterior pituitary is. In addition, it has a growth directed towards the hypothalamus, so its functions also differ from those of the rest of the structure.
Rather, the neurohypophysis is largely a collection of axonal projections from the hypothalamus leading to the posterior anterior pituitary. The main parts into which the pituitary is divided are the median eminence, the infundibulum and the pars nervosa, which we will talk about in the next point.
As for the elements or pieces that make up the mass of the neurohypophysis, it is made up of a series of cells called pituicytes, which can be considered glial support cells.
Finally, although at first glance the neurohypophysis may seem like just another hormone-secreting gland, in reality it is a kind of warehouse for the substances secreted in the hypothalamus.
Although it is true, the neuronal cells of the supraoptic and paraventricular hypothalamic nuclei secrete vasopressin and oxytocin that is stored in the vesicles of the axons of the neurohypophysis, which release these hormones in response to electrical impulses that arrive from the hypothalamus.
As mentioned above, the posterior pituitary, or neurohypophysis, consists mainly of neuronal projections of magnocellular neurosecretory cells that extend 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 part of them enter the circulation of the bloodstream, while others return to the pituitary system.
Although the differentiation of the various parts of the pituitary can vary according to classifications, most sources include the following three structures:
1. Middle 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.
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.
The infundibulum is the connection between the hypothalamus and the posterior pituitary. This 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 makes up most of the neurohypophysis and is the storage site for oxytocin and vasopressin. On many occasions this is considered a synonym of the neurohypophysis, however it is only a part of it.
Finally, some classifications also include the median pituitary as part of the neurohypophysis, but this is unusual.
Despite the fact that, as mentioned at the beginning of the article, on many occasions the neurohypophysis is mistakenly considered as a hormone-producing gland, its main function is not to synthesize these substances, but to store 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 through the bloodstream.
Oxytocin is a neuropeptide hormone which is characterized by playing an essential role in social ties, sexual reproduction in both sexes and being of vital importance both during and after childbirth.
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 contracting the arterioles, which increases peripheral vascular resistance and increases blood pressure.
In addition, it is also granted a possible third function related to the release of vasopressin in certain areas of the brain. This release could play an important role in social behavior, sexual motivation, bonding between people, and the mother’s response to stress.
What happens if it fails? Associated diseases
An injury, degeneration or alteration in the functioning of the neurohypophysis can result in a deregulation of the secretion of the two hormones described in the previous section.
Insufficient vasopressin secretion can lead to diabetes insipidus, a 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 diluted 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 secretion of antidiuretic hormone (SIADH), a disease of the neurohypophysis caused mainly by drugs and that causes all kinds of gastrointestinal and neuromuscular symptoms. , respiratory and neurological.