The two endocrine glands located on top of the kidneys are known as the adrenal glands. These two glands are responsible for releasing a number of hormones, including adrenaline and cortisol. Adrenal glands release these hormones directly into the bloodstream.
The adrenal gland can be divided into two parts - adrenal cortex and the adrenal medulla, or simply medulla. The adrenal cortex and the medulla have some specific functions. The adrenal gland is crucial for the smooth operation of several vital processes taking place in our body.
Understanding the Functions of Adrenal Cortex
The adrenal cortex is the outer layer of the adrenal gland, while the medulla is the inner or the central region. The outer cortex region is further divided into three zones or layers, known as zona glomerulosa, zona fasciculata, and zona reticularis.
The division of the adrenal cortex into these three layers is known as 'functional zonation'. Each layer of the adrenal cortex is associated with the production of some specific hormones.
The cortex region of the adrenal gland is associated with production of three types of hormones - glucocorticoids, mineralocorticoids, and androgen. The outermost layer of the cortex, i.e., zona glomerulosa is concerned with the production of mineralocorticoids, while the middle layer, zona fasciculata is responsible for producing glucocorticoid hormones.
The innermost layer, zona reticularis, is responsible for the synthesis of androgens. All these hormones perform some specific functions in the human body, and their over or underproduction is a symptom of adrenal problem.
Mineralocorticoids are steroid hormones produced by the zona glomerulosa layer of the adrenal cortex. The most important and common mineralocorticoid is aldosterone. One of the main functions of aldosterone is to regulate the levels of potassium and sodium in the body.
This hormone regulates the amount of potassium and sodium passed into the urine. Aldosterone is made from cholesterol and its production is controlled by the renin-angiotensin system (RAS) or renin-angiotensin-aldosterone system. This is a hormone concerned with the regulation of blood pressure, as well as fluid balance in the body.
Generally, renin is secreted by the kidneys when there is an excessive loss of salt and water from the body. Renin stimulates the production of angiotensin, which in turn, induces the adrenal glands to release aldosterone.
A condition of decreased blood pressure can trigger the secretion of aldosterone, which helps the kidneys retain important minerals like sodium, and raise blood pressure by increasing sodium and water retention. When the kidneys retain more sodium, more water is reabsorbed. This results in an increase in blood volume, which in turn raises the blood pressure.
The middle layer of the adrenal cortex synthesizes glucocorticoids like cortisol. Cortisol or hydrocortisone is also a steroid hormone, which performs several important functions. Cortisol plays an important role in the metabolism of carbohydrates, proteins, and fats.
This hormone signals the liver to make glucose and glycogen, and stimulates the adipose tissues to release lipids and fatty acids into the bloodstream. Cortisol also signals the skeletal muscles to release proteins or amino acids into the bloodstream. Glucocorticoids regulate the inflammatory response of the body as well.
Androgens or androgenic steroids are produced by the zona reticularis layer of the adrenal cortex. Androgens, including testosterone are male sex hormones, which assist the development of male characteristics, and the proper development of male sex organs during embryonic development.
Irregularities in the secretion of these hormones can cause several health problems or adrenal gland disorders. A number of medical conditions can interfere with the functions of the adrenal glands, of which Addison's disease and Cushing's syndrome are worth mentioning.
Addison's disease is characterized by the failure of the adrenal cortex, while Cushing's syndrome is caused by the excess secretion of cortisol.