Adrenal glands


The adrenal cortex and the adrenal medulla are often considered to be of similar function. However, both in structure and in function, these two structures are unique unto themselves. The adrenal medulla primarily secretes catecholamine hormones which are vital in the sympathetic actions of the autonomic nervous system. Corticosteroids are secreted by the adrenal cortex. These hormones are designed to regulate the balance of minerals, provide a balanced energy for human action, and have a significant role in the reproductive cycle.


The adrenal glands, also known as suprarenal glands, can be located along the superior edges of the kidneys. The adrenal glands are literally encased by the muscles of the back, protected by the pad of fat that surrounds them, just as the kidneys. This makes them retroperitoneal. The two adrenal glands are formed in the shape of a pyramid. Each one measures about 2 inches in length and just over an inch wide, with a depth of only 10 millimeters. The outer layer, which is the adrenal cortex, covers the inner layer, which is the adrenal medulla. Each layer is a separate gland.

The adrenal cortex is by far the largest portion of the gland, and in fact is determined in three subdivisions. The outer division, or “zone” is known as the zona glomerulosa. The inner division is known as the zona reticularis, and the middle zone is referred to as the zona fasciculata.


Special cells know as chromaffin cells are tightly packed in small clusters to comprise the adrenal medulla. These clusters are situated appropriately around the blood vessels. Each individual cluster of packed cells is specifically autonomically innervated. The adrenal glands demand a high level of vascular supply, just as the entire endocrine system. To meet the excessive demands, there are three individual suprarenal arteries that maintain the blood supply to the adrenal glands. The first one is derived from a branch of the inferior phrenic artery. The second branches from the renal artery. The third artery is a branch directly from the aorta. The venous return from this high demand released from the right adrenal gland flows into the suprarenal vein and directly into inferior vena cava. The left adrenal gland flows back through the suprarenal vein and then into the left renal vein. Preganglionic neurons derived from the splanchnic nerves which innervate the adrenal glands along with the celiac fibers and the associated sympathetic plexus.


Adrenal Glands
Image: Adrenal Glands


The adrenal cortex delivers over 30 previously identified hormones into the body’s bloodstream. The hormones released and secreted by the adrenal cortex are known as corticosteroids (corticoids) and are segregated into three functionally varying divisions. Mineralocorticoids, glucocorticoids, and gonadocorticoids all serve a basic function via different secretions. The zona glomerulosa is responsible for the secretions known as mineralocorticoids. These hormones basically regulate the varying levels of extracellular electrolytes within the cell structures. This layer is known to administer three different hormones, yet by far, the most vital of these three hormones is considered to be the aldosterone hormone. Aldosterone target the kidneys and initiates the organ’s ability to reabsorb sodium and to emit potassium into the body. It also encourages absorption of excess water and influences urine output, often initiating lower levels of urine excretion. The zona fasciculata is responsible for administering glucocortoids.

These hormones target the metabolic rate in reference to fats, proteins, and carbohydrates. Additionally, these hormones are known to initiate constriction of the blood vessels when necessary as well as assist the body in alleviate the various stress it finds itself under. There are numerous hormones that contain anti-inflammatory agents to help provide relief of pain in injury and deformation sites. Hydrocortisone (cortisol) has been determined to be the most vital of the hormones administered from the zona fasciculata. It is not only the most vital to the body physiological health, it is also the most abundant of the hormones secreted by this region of the adrenal cortex.

The final division, the zona reticularis, is responsible for administering the hormones known as gonadocorticoids. These hormones target the reproductive regions of the human body. While the vast majority of hormones secreted by this layer are deemed to be adrenal androgens, a small percentage of adrenal estrogens and progesterones have been discovered. These hormones work cohesively with other hormones to initiate the libido as well as initiate the production and maturation of the gonads in both the male and female body.


The cells of the adrenal medulla are known to produce two essential and closely related hormones. Epinephrine and norepinephrine are similar in both function and structure, and are technically classified as amines. They most specifically belong to the group of hormones referred to as catecholamines. These two hormones are known to sort of mimic the sympathetic division of the autonomic nervous system. Their effects are much longer lasting than the initial impulses sent by the autonomic nervous system. The chromaffin cells release hormones which can increase heart rhythm, enhance mental awareness, dilate the coronary blood vessels, enhance the metabolic rate, and elevate the respiratory rate. Naturally, sympathetic neurons innervate the adrenal medulla. Stress initiates a response from the spinal cord which in turn initiated reaction from the hypothalamus. Stress can be a single determining factor in initiating reactions from both the adrenal cortex and the adrenal medulla. The adrenal medulla is designed to initiate the body into a flight or fight response, and can keep the body in a state of preparedness for an indefinite amount of time.
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