Functions of Adrenal Gland

Adrenal glands also known as suprarenal glands, are triangular-shaped glands located on top of each kidney. They are one of the endocrine glands, others being the pituitary gland, pineal, thymus, ovaries, testes, thyroid and pancreas. The main characteristic of endocrine glands is that they secrete their hormones directly into the blood stream, while other glands release hormones into ducts that carry them to the blood stream.

Understanding Adrenal Glands

The adrenal glands can be divided into two parts, the outer region and the inner region. The outer region is known as adrenal cortex, which is further divided into three zones: Zona glomerulosa, the outermost layer, Zona fasciculata, the middle layer, and Zona reticularis, the innermost layer. Division of adrenal cortex into these three zones is also known as 'functional zonation'. The inner or the central region of the adrenal gland is known as adrenal medulla, which is surrounded by the cortex region. Blood is supplied to the adrenal glands through the adrenal arteries.

Both of its regions are centers of production of some vitally important hormones, having specific functions. Some important hormones secreted by them are as follows:

Aldosterone hormone
Aldosterone hormone is secreted by the glomerulosa zone (outermost layer) of the adrenal cortex. Its main function is to regulate the amount of potassium, and sodium passed into the urine. Its production is controlled by the renin angiotensin system (RAS) or renin angiotensin aldosterone system (RAAS). This is a hormone system that regulates blood pressure and fluid balance in the body. Generally renin is produced by the kidneys in the conditions of excess loss of salt and water from the body. Renin in turn, triggers the production of angiotensin, which ultimately stimulates the adrenal glands to release the aldosterone hormone. Decreased blood pressure also stimulates the secretion of aldosterone. So, together with the renin angiotensin system, aldosterone assists the kidneys to retain important minerals like sodium and potassium. It can also constrict the blood vessels, by increased sodium and water retention, and thereby increase blood pressure.

Hydrocortisone and corticosterone
Corticosteroids are released from the cortex region of the adrenal glands. Corticosteroid hormones secreted by the adrenal glands include hydrocortisone hormone and corticosterone. Hydrocortisone or cortisol regulates carbohydrate, protein and fat metabolism. Both hydrocortisone and corticosterone play important roles in regulating the inflammatory response of the body. Corticosterone can also affect the immune system, and hence can be used as an immune suppressing agent. Its secretion is controlled by the adrenocorticotropic hormone (ACTH), secreted by the pituitary gland.

Androgenic steroids
Androgenic steroids or androgens are secreted by the reticularis zone (innermost layer) of the adrenal cortex. They are the male sex hormones and are responsible for the development of male characteristics. They play a crucial role in the development of male sex organs during embryonic development.

Epinephrine and norepinephrine
These hormones are secreted by the inner part of the adrenal gland, i.e. the adrenal medulla, and are commonly known as adrenaline. They are called catecholamines, as they are released by the adrenal glands in response to physical or mental stress. Epinephrine, also known as adrenaline plays an important role in the conversion of glycogen into glucose. It is also required by the body for the smooth flow of blood to the brain and the muscles. Besides, it also increases the heart rate and relaxes the smooth muscles of the lungs and digestive system decreases blood sugar level. It also causes dilation of the small arteries of the heart, lung, kidneys and muscles. In short, it gears up the body for a fight/flight response.

Along with epinephrine, norepinephrine also activates the body mechanism for a fight/flight response, by increasing alertness and arousal. However, when injected as a drug, norepinephrine or noradrenaline can have a constrictive effect on the coronary arteries. It causes constriction of the small arteries of the kidneys, digestive system, skin and also small veins. It facilitates the movement of food through the digestive system and increases perspiration. It also stimulates the release of glucose and flow of blood to the muscles.

To sum up, adrenal glands are responsible for secreting hormones essential for carrying out some important metabolic processes. Besides, they also help the body in dealing with physical and mental stress.