The adrenal gland, also known as the suprarenal gland, is an endocrine gland. An Italian anatomist Bartolomeo Eustachi was the first to describe adrenal glands in 1563-1564. Jean Riolan the Younger gave the suprarenal term and specified its location in 1629. The adrenal gland produces a variety of hormones like adrenaline, aldosterone etc. Its location is above the kidneys. It has an outer cortex and an inner medulla, and it arises from the mesoderm. Three types of hormones are released from the adrenal cortex: mineralocorticoids, steroid hormones and androgens. Mineralocorticoids regulate blood pressure and maintain electrolyte concentration. Glucocorticoids like cortisol help in maintaining metabolism. Androgens are converted to their functional form in the reproductive organs. 

Adrenal Gland Location

Adrenal glands are located on the top of both kidneys. 

• The right adrenal gland on the anterior is in proximity to the inferior vena cava and right lobe of the liver.
• The right adrenal gland on the posterior is in proximity to the right side of the diaphragm.
• The left adrenal gland on the anterior is in proximity to the stomach, pancreas and the spleen.
• The left adrenal gland on the posterior is in proximity to the left side of the diaphragm. 

Adrenal Gland Structure

Adrenal glands are present on the top of both kidneys. The right side adrenal gland is pyramidal in shape, and the left side adrenal gland is semilunar in shape. The dimensions of the adrenal glands are approximately 5 cm in length, 3 cm in width and up to 1 cm thick. The gland can be pale yellow with an average weight somewhere between 7-10 grams. There is a fatty tissue layer surrounding the adrenal gland known as the capsule. The adrenal gland consists of an inner medulla and the outer cortex. The cortex is derived from the embryonic mesoderm, and the medulla is derived from the ectodermal neural crest cells.

Cortex – It is generally pale yellow. It is known for secreting two very important hormones: corticosteroids and androgens. It can be further divided into –

• Zona glomerulosa – It is the outermost portion of the cortex, known for producing and secreting mineralocorticoids like aldosterone.
• Zona fasciculata – It is present between zona glomerulosa and zona reticularis. It is known to produce and secrete corticosteroids like cortisol. 
• Zona reticularis – It is the innermost part of the cortex and is present next to the medulla. It is known for producing androgens and corticosteroids in small amounts.

Medulla – It is present in the centre of the gland. It has chromaffin cells that are known for secreting catecholamines like adrenaline. It also secrets enkephalins, which work as a natural painkiller.

Hormones and their functions

The adrenal gland secretes and produces various hormones that are essential for the normal functioning of the body. A few of these hormones are:

• Cortisol is a glucocorticoid released from the zona fasciculata of the adrenal cortex. It helps in maintaining the fat, carbohydrate and protein usage in the body. It is known to suppress inflammation, maintain blood pressure (BP), decrease bone formation, and increase blood sugar levels. It also controls the circadian rhythm of the body.
• Aldosterone is a mineralocorticoid released from the zona glomerulosa of the adrenal cortex. It helps maintain blood pressure by regulating the concentration of the electrolytes in the body.
• Adrenaline and noradrenaline are secreted from the adrenal medulla and are commonly known as the fight and flight hormones. These hormones can increase the heart rate by vasoconstriction and increase blood flow to the muscles and brain. They also help maintain blood pressure.

Conclusion

The adrenal gland is an endocrine gland that is pale yellow. The adrenal gland is covered by a layer of fat tissue called the capsule. It was first described by an Italian anatomist Bartolomeo Eustachi in 1564. The gland is present above both kidneys, but they have different shapes. The gland present on the right is pyramidal, and the one on the left is semilunar. 

The adrenal gland can be further divided into two parts – the inner medulla and the outer cortex. The medulla releases two hormones, adrenaline and noradrenaline, known as the flight and fight hormones. They increase the heart rate during stress or excitement.

The three types of hormones released from the adrenal cortex are mineralocorticoids, steroid hormones and androgens. Mineralocorticoids regulate blood pressure and maintain electrolyte concentration. Glucocorticoids like cortisol help in maintaining metabolism. Androgens are converted to their functional form in the reproductive organs.