Despite their small size, the adrenals are very important glands for our health. Their task, in fact, is to secrete different hormones, capable of influencing the activity of the whole organism.
In addition to hormones, whose activity is mainly under pituitary control, the adrenal gland processes the enzymes necessary for their synthesis and their transformation. All steroid hormones, in fact, originate from a common precursor: cholesterol, which is then enzymatically transformed into glucocorticoids, mineralocorticoids and sex-active hormones. The metabolic pathways that lead to the synthesis of these hormones are the same in the adrenal cortex, in the gonads and in the placenta, what changes is only the concentration of the various enzymes; that responsible for the synthesis of aldosterone, for example, is expressed only in the glomerular region of the cortical portion of the adrenal gland.
Anatomical features
Height
30 mm
Length
45 mm
Thickness
6 mm
Medium weight
7-8 grams
The adrenal glands are two small glands located superior to the kidney, on either side of the last thoracic vertebra - first lumbar vertebra.
They consist of specialized neuroendocrine tissue, closely related to the sympathetic nervous system.
Their shape, although very variable, has been compared to that of a cone with a lower base or a Phrygian hat (conical headdress, with the tip folded forward).
Richly vascularized, they receive blood from the superior, middle and inferior adrenal arteries which derive, respectively, from the phrenic artery, the aorta and the renal artery.
The venous return is ensured by the adrenal vein, which flows to the left into the renal vein and to the right into the inferior vena cava.
Functions of the adrenal glands
Each adrenal gland is made up of two portions, one internal, the medulla, and one external, the cortex. The two regions have very different embryological origins and anatomical, histological and functional characteristics:
- the medullary portion of the adrenal gland constitutes about ¼ of the total mass of the gland, is softer, occupies the internal region and is responsible for the release of particular hormones, called catecholamines.
- The cortical portion envelops the medulla, covers the remaining ¾ of the glandular mass, is more consistent and secretes various steroid hormones. This region, also known as adrenal cortex or adrenal cortex, is in turn made up of three distinct portions in terms of structure and function: the reticular area, the fasciculated area and the glomerular area.
Adrenal hormones, cortical portion
The external glomerular area secretes aldosterone, a very important mineralocorticoid for the control of blood pressure. Aldosterone acts by increasing the reabsorption of sodium in the renal tubules and the excretion, again via the kidney, of potassium. More information in the dedicated article: aldosterone.
The intermediate fasciculated zone produces glucocorticoids, so called because they are capable of increasing the plasma concentration of glucose. The best known are cortisol and corticosterone, both synthesized by the adrenal gland in response to the pituitary hormone ACTH. These hormones are active in increasing blood sugar, the synthesis of glucose (gluconeogenesis) and glycogen (glycogenosynthesis), the mobilization of triglycerides reserve and the use of muscle amino acids for energy purposes. For further information: cortisol.
The deep reticular zone secretes mainly androgens (androstenedione), typical male sex hormones. Physiologically, in the male organism they are of little importance, because they are secreted in low quantities compared to what occurs at the testicular level. In women, on the other hand, they help regulate sexual desire, sebaceous secretion and the development of pubic and axillary hair. These hormones damage unequivocal signs of their presence when the adrenal gland goes crazy, for example due to a tumor or an enzyme deficiency, and begins to produce them in excess. The endocrine disorder thus created determines, in women, hirsutism, breast atrophy, clitoral hypertrophy, etc. More information in the dedicated article: androgens.
When the adrenal gland does not produce a sufficient amount of corticosteroid hormones, a pathology, known as Addison's disease, often on an autoimmune basis, takes place, which is treated by administering artificial hormones very similar to their natural counterpart.
Adrenal hormones, medullary portion
Summary scheme
of the hormones produced
from the adrenal gland, click
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zoom in
The medullary portion of the adrenal produces two important hormones, adrenaline and noradrenaline, which can be grouped under the single term "catecholamines".
The medullary region develops from the same embryonic tissue as sympathetic neurons and is considered a neuroendocrine structure. Its function, in fact, is controlled by the central nervous system, which does not rely on hormones but on nerve impulses to communicate with it. This control mechanism allows the lightning release of catecholamines at the time of need, for example when you are faced with a sudden danger, to be faced in the shortest possible time.
After being released into the blood, the adrenal catecholamines prepare the body for the required effort: they increase blood pressure, dilate the bronchi, accelerate heart rate, stimulate glycogen breakdown, increase blood sugar, accelerate breathing and inhibit intestinal peristalsis . Learn more about the catecholamines produced by the adrenal gland in the dedicated article.
