Vitamin C is crucial for the proper functioning of the adrenal or suprarenal glands. This vitamin is required for producing the adrenocortical steroid hormones.
Adrenal glands, also known as suprarenal glands, are located on top of each kidney. Adrenal glands are endocrine glands, as they secrete their hormones directly into the bloodstream, while other glands release hormones into ducts that carry them to the bloodstream.
Despite their small size, the suprarenal glands help maintain homeostasis (metabolic equilibrium), by regulating the functions of the tissues, and various organs and glands. Some of the hormones released by these glands are crucial for human life. So, let's find out more about the structure and functions of the adrenal glands.
Structure of the Adrenal Glands
Each adrenal gland sits on top of each kidney on a pad of fat. Each adrenal gland can be divided into 2 parts - the outer cortex region and the inner medulla region.
The outer region, i.e., the 'adrenal cortex' is further divided into three zones - Zona glomerulosa (the outermost layer), Zona fasciculata (the middle layer) and Zona reticularis (the innermost layer). The division of the adrenal cortex into these three zones is known as 'functional zonation'.
The inner or the central region of the adrenal gland is known as 'adrenal medulla', which remains surrounded by the cortex region. Blood is supplied to the adrenal glands through the adrenal arteries.
Both the cortex and the medulla are concerned with the production of some important hormones, which perform some specific functions. The hormones secreted by the adrenal cortex are crucial for life, while those released by the adrenal medulla are not.
Functions of the Adrenal Cortex
The functions of the adrenal glands are regulated by the hypothalamus and the pituitary gland. The hypothalamus releases the corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH induces the adrenal glands to produce corticosteroid hormones.
The adrenal cortex is basically responsible for synthesizing three types of hormones, which are known as:
Functions of Mineralocorticoids
Mineralocorticoids are steroid hormones responsible for conserving sodium, and maintaining salt and water balance in the body. The primary mineralocorticoid is known as aldosterone, and it is secreted by the zona glomerulosa (outermost layer) of the adrenal cortex.
This steroid hormone is a part of 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 when excess salt and water are lost from the body. Renin triggers the production of angiotensin, which ultimately stimulates the adrenal glands to release the hormone aldosterone. A decrease in arterial blood pressure also stimulates the secretion of renin.
So, together with the renin-angiotensin system, aldosterone assists the kidneys to retain important minerals like sodium. Aldosterone increases the reabsorption of sodium and the excretion of potassium by the kidneys.
It helps constrict the blood vessels by increasing the retention of sodium and water, which in turn, can raise the level of blood pressure. So, this hormone is concerned with regulating the level of blood pressure as well.
Functions of Glucocorticoids
Glucocorticosteroids are another class of steroid hormones that play a crucial role in regulating glucose metabolism. Glucocorticosteroids are classified into two categories - hydrocortisone and corticosterone, which are produced in the zona fasciculata of the adrenal cortex.
Hydrocortisone or cortisol is responsible for regulating the metabolism of carbohydrate, protein, and fat. Both hydrocortisone and corticosterone play important roles in regulating the inflammatory response of the body.
Corticosterone can affect the immune system, and it can be used as an immune-suppressing agent. Its secretion is controlled by the adrenocorticotropic hormone (ACTH) secreted by the pituitary gland.
Functions of Gonadocorticoids
Gonadocorticoids or androgenic steroids are secreted by the zona reticularis or the innermost layer of the adrenal cortex. Androgens are male sex hormones, and they facilitate the development of secondary sexual characteristics in men. They play an important role in the development of male sex organs during embryonic development.
A small amount of female hormones are also produced by the adrenal cortex. However, the effects of the androgenic steroids secreted by the adrenal cortex get overshadowed by the greater amounts of testosterone and estrogen secreted by the testes and the ovaries respectively.
Functions of the Adrenal Medulla
The medulla is the inner portion of the adrenal gland, and it is mainly concerned with the production of epinephrine and norepinephrine, which perform the following functions.
Functions of Epinephrine and Norepinephrine
Both epinephrine and norepinephrine are together called catecholamines, and 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, and thus, raises the level of blood sugar. It is required by the body for maintaining the smooth supply of blood to the brain and the muscles.
It can also increase the heart rate and blood pressure, and relax the smooth muscles of the lungs and the digestive tract. This hormone dilates the small arteries of the heart, lungs, kidneys, and the muscles.
Excitement, physical and mental stress, and emotional disturbances trigger the secretion of this hormone, which prepares our body for the 'fight or flight' response.
Along with epinephrine, norepinephrine also activates the mechanism for a 'fight or flight' response, by increasing alertness and arousal. When injected as a drug, norepinephrine or noradrenaline can have a constrictive effect on the coronary arteries.
It causes the small blood vessels of the kidneys, digestive system, and the skin to constrict. It facilitates the movement of food through the digestive system and increases perspiration. It also stimulates the release of glucose and the flow of blood to the muscles.
To sum up, adrenal glands are responsible for secreting hormones essential for carrying out some important metabolic processes. Moreover, they help the body deal with physical and mental stress. Chronic stress can make the gland work so hard that it can eventually exhaust or become too fatigued to meet the requirement of the adrenal hormones.