Neurohypophysis: structure, functions and associated diseases

Our body and the organs that compose it work in harmony, like a clockwork machine, to maintain our physical health and so that all the functions and activities of the body can be developed efficiently.

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

    What is the neurohypophysis?

    Within the endocrine system, made up of a large number of organs and hormone-functioning structures, we find the neurohypophysis. This organ forms 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 like the previous pituitary gland is. In addition, this it has a growth directed towards the hypothalamus, So that their functions also differ from those of the rest of the structure.

    In contrast, the neurohypophysis is largely a collection of axonal projections from the hypothalamus that flow into the posterior area of ​​the anterior pituitary. The main parts into which the pituitary gland is divided are the middle eminence, the infundibulum and the nerve pair, which we will talk about in the next point.

    As for the elements or parts that make up the mass of the neurohypophysis, this it is made up of a series of cells called pituicytes, Which can be considered to support the glial cells.

    Finally, although at first glance the neurohypophysis may look like another hormone-secreting gland, it is actually a kind of storehouse of secreted substances in the hypothalamus.

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

      structure

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

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

      Although the differentiation of different parts of the pituitary gland can vary depending on the classification, most sources include the following three structures:

      1. Middle Eminence

      The area of ​​the neurohypophysis known as the middle eminence is that which is attached to the infundibulum. It 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 middle eminence is to act as a gateway for the release of hypothalamic hormones. However, it also shares continuous perivascular spaces with the adjacent arched hypothalamic nucleus, indicating a possible sensory role.

      2. Infundible

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

      3. Nerve pair

      Also known as the neural lobe or posterior lobeThis region makes up most of the neurohypophysis and is the storage site for oxytocin and vasopressin. In many cases, it is considered to be synonymous with neurohypophysis, but this is only part of it.

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

      functions

      Although, as mentioned at the beginning of the article, the neurohypophysis is often confused with a hormone-producing gland, its main function is not to synthesize these substances, but to store them and the release of the two hormones conventionally linked to this organ: oxytocin and vasopressin.

      At first, these hormones are synthesized in the hypothalamus, transported and released in the posterior pituitary. After their production, they are stored in clustered neurosecretory vesicles, before being secreted into the neurohypophysis by the bloodstream.

      1. Oxytocin

      Oxytocin is a neuropeptide hormone characterized by exercise an essential role in social bonds, sexual reproduction in both sexes and being of vital importance 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 contracting arterioles, which increases peripheral vascular resistance and increases blood pressure.

      In addition, it is also given a possible third function linked to the release of vasopressin in certain areas of the brain. This release could play an important role in social behavior, sexual motivation, interpersonal bonds and the mother’s reaction to stress.

      What if it fails? associated diseases

      Injury, degeneration or impaired functioning of the neurohypophysis can lead to deregulation of the secretion of the two hormones described in the previous section.

      Insufficient vasopressin secretion this can lead to the development of diabetes insipidus, A condition in which the body loses the ability to store and concentrate urine and which allows 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 the syndrome of inadequate antidiuretic hormone secretion (SIADH). a disease of the neurohypophysis caused mainly by drugs and it causes all kinds of gastrointestinal, neuromuscular, respiratory and neurological symptoms.

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