Adrenals

What are the adrenals?
The adrenal glands are part of the endocrine system i.e. they are ductless glands. They lie above the kidneys and hence are also called as suprarenal glands. They are two in number and secrete many important hormones.

Where are the adrenals located?
The adrenals are located one each at the upper end or upper pole of the kidneys. Therefore there is a left adrenal gland and a right adrenal gland. The other abdominal organs like the intestines and peritoneum lie above the adrenals.

How can we describe the adrenals?
The adrenals are medium sized glands, yellowish in color and are separated slightly from the kidney by a layer of fat. The right adrenal is pyramidal in shape while the left one is crescentic in shape.

Internal structure of the adrenals : When a adrenal gland is cut open vertically, two areas are clearly demarcated. These are the outer yellowish cortex and the inner brownish medulla or core. Both are specialized areas secreting different hormones.

Functions of the adrenals

The adrenals, like the other endocrine organs secrete hormones. The cortex or the outer part secretes several steroid hormones. The pituitary controls this part of the adrenal gland. The steroid hormones secreted by the cortex are:

1. Mineral corticoids: These hormones are concerned with the fluid and electrolyte balance of the body. Aldosterone is the most important of the mineral corticoids. It acts on the kidneys and regulates excretion of salt from the body to maintain our blood pressure.
2. Glucocorticoids: These hormones are concerned with the metabolism of starch, proteins and fats. Cortisol is the most important of the glucocorticoids. It increases the blood glucose levels thereby adapting the body to physically and emotionally stressful situations.

The medulla or the core of the adrenals secretes the hormones epinephrine and nor-epinephrine. These are collectively called as the catecholamines. Epinephrine is secreted in larger quantity (80%) than nor-epinephrine (20%). These hormones increase the blood supply to the muscles and increase the heart rate. This readies the body to take a quick decision in stressful situations. This is called as the characteristic, ‘fright, fight, or flight’ response in a human being. Hence the person responds to a stressful situation first by reacting with fright and then decides to run away from the site or stay there and face it. Hence this hormone plays a very important role in day to day life.

The hormone epinephrine has the capability of increasing the metabolic rate of every cell in the body even if that cell is not connected to the nervous system by any nervous pathway.