FUNCTION OF MINERALOCORTICOIDS

In this lesson from a TEACHER we will see what is the role of mineralocorticoids. But first we will give a brief review of the structure of the gland that produces this type of hormones and the characteristics of these steroidal compounds, in order to better understand the functions that develop.

Index

1. Mineralocorticoids and the adrenal glands
2. What are mineralocorticoids?
3. What is the function of mineralocorticoids?
4. How are MC levels controlled?: The Renin-Angiotensin-Aldosterone System

Mineralocorticoids are hormones created by Kidney glands, two pyramidal glands located on top of both kidneys. Its average weight is 4 grams, but it increases significantly in states of stress.

The adrenal glands are made up of two well-differentiated tissues that fulfill different functions: the inner medulla and the outer cortex.

Internal medulla

It is the innermost area of ​​the adrenal gland. The adrenal medulla is formed from neural tissue and is made up of modified nerve cells and nerve fibers that connect it directly to the sympathetic autonomic nervous system. In the adrenal medulla a complex mixture of

Outer cortex

The adrenal cortex is controlled by the trophic hormones of the pituitary, such as ACTH and growth factors. The outer cortex produces three types of hormones: adrenal glucocorticoids, mineralocorticoids (MC) and sex steroid hormones. All of these hormones are steroid hormones that are synthesized from the cholesterol molecule.

It consists of several areas of differentiated tissue, where they are synthesized different types of hormones:

• Glomerulous zone: It is the outermost area of ​​the gland and represents 15% of the cortex. In this area of ​​the adrenal cortex the aldosterone, the most important mineralocorticoid in humans and other mineralocorticoids such as deoxycorticosterone (DOC)
• Fascicular zone: It is the most extensive area of ​​the crust, representing 75% of the total. It is located below the zona glomerulosa. In this area of ​​the cortex, the synthesis of glucocorticoids, mainly cortisol and corticosterone.
• Reticular zone: It is the innermost area of ​​the cortex, in contact with the inner medulla and it is also the thinnest layer of the cortex of which it represents only 10%. In this area of ​​the adrenal cortex, they are synthesized sex hormones (androgens, estrogens and progestogens).

Mineralocorticoids are synthesized steroid hormones and secreted by the zona glomerulosa of the adrenal cortex and acting on the electrolyte balance of the plasma, especially by the sodium and chlorine reabsorption in the renal tubules.

In mammals, the main mineralocorticoid (MC) is the aldosterone which plays a fundamental role in electrolyte control and water distribution in tissues. Another mineralocorticoid synthesized in the adrenal cortex is deoxycorticosterone (DOC) from which aldosterone is synthesized.

All mineralocorticoids (MC) produce two effects aimed at increasing Na + retention in the body and reducing water loss.

We are going to enter fully into the function of mineralocorticoids and we will analyze the main and secondary ones.

Electrolyte balance control

As its name indicates, the fundamental role of mineralocorticoids consists in the regulation of salt (mineral) and water levels in the body. That is, they are essential for electrolyte balance, which is the balance of the amount of dissolved salts (electrolytes) and water that the body contains.

We speak of "equilibrium" because it is about parameters that are influenced by a multitude of internal factors and external to the body and that, however, must be kept within very strict parameters to guarantee the maintenance of life. Due to its vital importance, aldosterone levels are controlled by mechanisms that guarantee its suitability at all times, it is the Renin-Vasopressin-Aldosterone system.

Other MC functions

Another effect of MCs, particularly aldosterone, is the increased glycolysis.

Aldosterone also has other physiological functions such as increased deposition of glycogen in the liver, decreased eosinophils (cells of the immune system) and resistance to stress.

Aldosterone levels are controlled by the so-called Renin-Angiotensin-Aldosterone system. It is a system made up of three components:

Renin

The first component of the system is Renin, an enzyme (biocatalyst protein) synthesized in the kidney by special cells called cells of the juxtaglomerular apparatus. The cells of the juxtaglomerular apparatus are capable of detecting changes in arterial volume (amount of blood that circulates through the arteries). When these kidney cells detect decreasing Na + o levels at low blood volume, release Renin into the circulatory system.

Angiotensin

In the bloodstream, Renin catalyzes the reaction of a plasma protein of liver origin to give rise to Angiotensin I. In a second reaction, on which another enzyme acts, Angiotensin I is transformed giving rise to Angiotensin II, which is a powerful vasoconstrictor. Angiotensin II acts on multiple tissues contributing to the regulation of mean arterial pressure, causing an increase in blood pressure by various mechanisms.

In the kidney, Angiotnsin II, stimulates the reabsorption of Na + and water through two mechanisms, one direct and the other indirect:

1. Angiotensin II stimulates tubular function (at the level of the proximal tubule and Hendle's Loop) increasing Na absorption⁺) and water directly.
2. In addition, Angiotensin indirectly develops this function, stimulating the release of aldosterone.

Aldosterone

Aldosterone is the main MC in humans. When this hormone is released into the bloodstream, it causes two mechanisms aimed at increasing electrolyte and water retention.

One of the mechanisms that triggers Aldosterone is the increase in Na reabsorption⁺, other electrolytes such as Cl^- and water; at the level of the distal tubule and the collector kidney.

The second mechanism occurs at the level of sweat glands, salivary glands, and the intestine, where the presence of Aldosterone causes the reduction of water loss.

In the sweat and salivary glands, Aldosterone causes the same effects as at the level of the renal tubules. These two glands produce primary secretions that contain large amounts of salt (NaCl). When Aldosterone levels are high, the reabsorption of Na + and Cl- ions occurs, while K + and bicarbonates are excreted.

In the case of the intestine, the reabsorption of water occurs mainly at the level of the colon, preventing its loss through the feces. The absence of Aldosterone in the intestine prevents the correct absorption of water and electrolytes and causes diarrhea.

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• Jara Albarrán A. coordinator. (2011) Endocrinology. 2nd ed. Madrid: Panamerican Medical.
• Patricia E. Molina (2008) Endocrine physiology. Mexico [etc.]: McGraw-Hill