Adrenal

Adrenal glandula (glandula suprarenalis) - the paired organ is located in the retroperitoneum directly above the upper end of the corresponding kidney. The adrenal gland has the form of a flattened front-to-back irregularly shaped cone. The right adrenal gland, viewed from the front, looks like a triangle with rounded corners. The apex of the left adrenal gland is smoothed, it resembles a crescent in shape. Each adrenal gland has a facies anterior, a facies posterior and a facies renalis.

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Anatomy of the adrenal glands

The adrenal glands are located at the level of the XI-XII thoracic vertebrae. The right adrenal gland, like the kidney, lies somewhat lower than the left one. Its posterior surface is attached to the lumbar part of the diaphragm, its anterior surface comes into contact with the visceral surface of the liver and duodenum, and the lower concave (renal) surface - with the upper end of the right kidney. The medial margin (margo medialis) of the right adrenal gland is bordered by the inferior vena cava. The left adrenal gland is in contact with the medial margin with the aorta, the anterior surface is attached to the tail of the pancreas and the cardiac part of the stomach. The posterior surface of the left adrenal gland is in contact with the diaphragm, the lower one with the upper end of the left kidney and its medial margin. Each adrenal gland (both right and left) lies in the thickness of the periphrenic fat body. The anterior surfaces of the left and right adrenals are partially covered with the renal fascia and the parietal peritoneum.

The weight of one adrenal gland in an adult is about 12-13 g. The length of the adrenal gland is 40-60 mm, the height (width) is 20-30 mm, the thickness (anteroposterior size) is 2-8 mm. The mass and size of the right adrenal gland is slightly less than the left one.

Sometimes in the body there is an additional ectopic tissue of the cortical layer of the adrenal glands (in the kidneys, spleen, retroperitoneal area below the kidneys, along the aorta, in the pelvis, in the seminal cord, in the wide ligament of the uterus). Perhaps the congenital absence of one of the adrenal glands. A characteristic feature of their cortical substance is its ability to regenerate.

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The structure of the adrenal glands

Surface of the adrenal gland slightly bumpy. On the front surface, especially the left adrenal gland, there is a deep furrow - the hilum, through which the central vein emerges from the organ. Outside, the adrenal gland is covered with a fibrous capsule, tightly joined to the parenchyma and giving numerous connective tissue trabeculae into the interior of the organ. To the fibrous capsule from the inside is a cortex (cortex, cortex) that has a rather complex histological structure and consists of three zones. Outside, closer to the capsule, is the glomerular zone (zona glomerulosa), behind it - the middle fascicle zone (zona fasciculate), on the border with the brain substance there is an internal reticular zone (zona reticularis). The morphological peculiarity of the zones is the distribution of glandular cells, connective tissue and blood vessels peculiar to each zone.

The cortical layer in an adult man accounts for about 90% of adrenal tissue. This layer consists of three zones: outer - glomerular, middle - bundle and inner (surrounding the medulla) - reticulate. Located directly under the fibrous capsule, the glomerular zone occupies approximately 15% of the volume of the cortical layer; its cells contain a relatively small amount of cytoplasm and lipids, produce a hormone aldosterone. The beam zone accounts for 75% of the total cortical substance; its cells are rich in cholesterol and cholesterol esters, they produce mainly cortisol (hydrocortisone). Cells of the reticular zone also produce this substance; they are relatively poor in lipids and contain many granules. In addition to cortisol, the cells of this zone (like the beam) produce sex hormones - androgens and estrogens.

In the cortical layer of the adrenal gland, more than 50 different steroid compounds are produced. It serves as the only source of gluco- and mineralocorticoids in the body, the most important source of androgens in women and plays an insignificant role in the production of estrogens and progestins. Glucocorticoids, named after the ability to regulate carbohydrate metabolism, are important for maintaining many vital functions and especially to ensure the body's response to stress. They are also involved in the regulation of growth and development. The main glucocorticoid in humans is cortisol, and the excess or deficiency of this steroid is accompanied by life-threatening shifts. Of mineralocorticoids (named so by the ability to regulate the exchange of salts), the basic in humans is aldosterone. Excess of mineralocorticoids causes arterial hypertension and hypokalemia, and a deficiency is hyperkalemia, which may be incompatible with life.

The glomerular zone is formed by small, prismatic forms of cells located in the form of small groups - glomeruli. In these cells, the endoplasmic reticulum is well developed, lipid droplets about 0.5 μm in size are present in the cytoplasm. The glomeruli are surrounded by convoluted capillaries with a fenestrated endothelium.

The fascicle zone (the widest part of the adrenal cortex) consists of large bright polyhedral cells. These cells form long strands (bundles) oriented perpendicular to the surface of the adrenal gland. In the cells of this zone, the ungrain endoplasmic reticulum is well developed, mitochondria, numerous lipid droplets, ribosomes, particles of glycogen, cholesterol and ascorbic acid are present. Between the strands of endocrine cells are blood capillaries with fenestrated endothelium.

The net zone is made up of small polyhedral and cubic cells forming small cell clusters. Cells of the reticular zone are rich in elements of an ungrain endoplasmic reticulum and ribosomes.

The listed zones are functionally isolated. The cells of each zone produce hormones that differ from each other not only in chemical composition, but also in physiological action. The hormones of the cortical substance of the adrenal glands are called corticosteroids and can be divided into three groups: mineralocorticoids - aldosterone, secreted by the cells of the glomerular cortex; glucocorticoids : hydrocortisone, corticosterone, 11-dehydro- and 11-deoxycorticosterone, formed in the bundle zone; sex hormones - androgens, in structure and function close to the male sex hormone, estrogen and progesterone, produced by the cells of the reticular zone.

Aldosterone is involved in the regulation of electrolyte and water metabolism, changes the permeability of cell membranes for calcium and sodium, stimulates the formation of collagen. Glucocorticoids affect protein metabolism, increase the glucose level in the blood, glycogen in the liver, skeletal muscles, myocardium. Glucocorticoids also accelerate filtration in the glomeruli of the kidney, reduce the reabsorption of water in the distal convoluted tubules of the nephrons, inhibit the formation of the main substance of connective tissue and the proliferation of fibroblasts.

In the center of the adrenal gland is a medulla, formed by large cells, colored with chromium salts in a yellowish-brown color. There are two varieties of these cells: epinephrotocytes make up the bulk of cells and produce adrenaline, norepinephrlets scattered in the brain in the form of small groups, produce norepinephrine.

Adrenaline cleaves glycogen, reduces its reserves in muscles and liver, increases the carbohydrate content in the blood, being an insulin antagonist, strengthens and increases the contraction of the heart muscle, narrows the lumen of blood vessels, thereby increasing blood pressure. The effect of norepinephrine on the body is similar to that of adrenaline, but the effect of these hormones on certain functions can be quite the opposite. Norepinephrine, in particular, slows the frequency of cardiac contractions.

Development of the adrenal glands

The cortical and medulla of the adrenal gland are different in origin. The cortical substance is differentiated from the mesoderm (from the coelomic epithelium) between the root of the dorsal mesentery of the primary intestine and the urogenital fold. Developing from the mesodermal cells and located between the two primary buds, the tissue was called interrenal. It gives rise to the cortical substance of the adrenal glands, additional adrenals (interrenal bodies, glandulae suprarenales accessoriae) are formed from it.

The adrenal medulla develops from embryonic nerve cells - sympatoblasts, which are evicted from the bookmark of the nodes of the sympathetic trunk and turn into chromaffinoblasts, and the latter into chromaffin cells of the brain substance. Chromaffinoblasts also serve as a material for the formation of paraganglia, which in the form of small accumulations of chromaffin cells are located near the abdominal aorta - aortic paraganglion aorticum, as well as in the thickness of sympathetic trunk nodes - sympathetic paraganglia (paraganglia sympathica).

The introduction of future brain cells into the interrenal adrenal gland begins in a 16 mm embryo. Simultaneously with the combination of the interrenal and adrenal parts, the zones of the cortical substance are differentiated and the maturation of the brain substance is differentiated.

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Vessels and nerves of the adrenal glands

Each adrenal gland receives 25-30 arteries. The largest of these are the upper adrenal arteries (from the lower diaphragm artery), the middle adrenal (from the abdominal part of the aorta) and the lower adrenal (of the renal artery) artery. Some of the branches of these arteries supply only the cortex, while others perforate the cortical substance of the adrenal gland and branch out into the brain substance. From the sinusoidal blood capillaries, infusions of the central vein are formed, which in the right adrenal gland runs into the lower vena cava, at the left - into the left renal vein. Of the adrenals (especially the left adrenals) there are numerous small veins flowing into the inflows of the portal vein.

Lymphatic vessels of the adrenal gland go into the lumbar lymph nodes. In the innervation of the adrenal glands, wandering nerves, as well as nerves originating from the celiac plexus, which contain preganglionic sympathetic fibers for the medulla, are involved.

Age features of the adrenal glands

A primitive adrenal cortex is formed in a retroperitoneal mesenchyme in a 5-6 week old fetus. Soon it is surrounded by a thin layer of more compact cells. The newborn adrenal cortex consists of two zones - fetal and definitive. The first produces mainly the predecessors of androgens and estrogens, whereas the function of the second, probably, as in an adult. The fetal zone accounts for the bulk of the fetal and newborns glands. By the second week of postnatal life, her weight is reduced by a third due to degeneration of the fetal zone. This process begins in the intrauterine period. The entire fetal zone disappears by the end of the first year of life. The final formation of the three zones of the adrenal cortex is prolonged to 3 years of age. Then the adrenal glands continue to increase (especially before and during pubertal) and reach the age of adulthood by the end of puberty.

The weight of one adrenal gland in a newborn is about 8-9 g and significantly exceeds the weight of the adrenal gland of the first year of life. During the neonatal period, the adrenal mass decreases sharply (to 3.4 g), mainly due to thinning and reorganization of the cortex, and then gradually restored (by 5 years) and continues to grow in the future. The final formation of the cortical substance of the adrenal glands is completed during the second childhood (8-12 years). By the age of 20, the mass of each adrenal gland increases and reaches its maximum size (on average, 12-13 g). In subsequent ages, the size and weight of the adrenal glands do not change much. Adrenal glands in women are somewhat larger than in men. During pregnancy, the mass of each adrenal gland increases by about 2 g. After 70 years, there is a slight decrease in the mass and size of the adrenal glands.

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