TThe adrenal glands are small glands, which sit on top of the kidneys and are responsible for producing many hormones that are essential to life.

The adrenal gland is divided into 2 areas the Cortex and the Medulla. The cortex is dived into 3 more zones each of which produce different hormones. The outer zone (Zona Glomerulosa) produces mineralcorticoids mainly aldosterone, the middle zone (zona faciculata) produces glucocorticoids mainly cortisol and the inner zone (zona reticularis) makes small amount of weak androgens, steroid hormones that have a masculising effects.

Adrenal Cortex Hormones

Mineralcorticoids -  These hormone help the body to control water and electrolyte balance in the body, particularily the concentration of sodium ions (Na+) and potassium ions (K+). There are atleast 3 different mineralcorticoids released by the adrenal galnds but 95% of the mineralcorticoid activity is due to Aldosterone. Aldosterone has an effect on the kidneys to increase the reabsorption of Na+. The reabsorbtion of Na+  also leads to the reabsorption on Cl^- (chloride ions) and HCO₃^-(bicarbonate ions) and water. At the same time aldosterone promotes the kidneys to increase secretion of K+ and H+ into the urine – this removal of acids from the body helps it to maintain a stable pH and prevent acidosis which is when the blood is getting too acidic (pH below 7.35).

Glucocorticoids – These hormones help to regulate metabolism and resist stress. They include Cotisol, Corticosterone and Cortisone. By far the most important of these is cortisol and about 95% or glucocorticoid production is of cortisol. These hormone have many roles in the body:

1.   Breakdown of proteins - Glucocorticoids increase the rate of protein breakdown, mostly in muscle fibre which release amino acids into the blood stream. The amino acids can then be used by the liver cells to make new proteins such as enzymes for metabolic reactions or by other cells for ATP (energy) production.

2.   Gluconeogenesis - This where the liver will produce glucose from amino acids or lactate.

3.   Lipolysis – Glucocorticoids stimulate the breakdown of triglycerides and fatty acids from adipose tissue.

4.   Resistance to Stress – By providing tissue with energy via ATP this helps the body to combat a range of stressors including fasting, exercise, fright, temperature extremes, pain, altitude, infections, trauma and disease because they also make blood vessels more sensitive they cause vasoconstriction and therefore high blood pressure.

5.   Anti-inflammatory effects – Glucocorticoids are anti inflammatory they will 1.reduce the number of mast cells (a type of immune cell which releases histamine) 2. Stabilise lysosomal membranes which slows the relese of inflammatory enzymes 3. Decrease capillary permeability reducing swelling 4. Depress phagocytosis (the action of certain immune cells) – On the other side of this coin they will also slow down wound healing and and connective tissue repair.

Androgens – In both males and females the adrenal glands secrete small amounts of androgens the major androgen secreted is DHEA (dehydroepiandosterone). In Adult males the amount of androgens secreted by the adrenal glands is small. In female the effects of androgens released by the adrenal glands play important roles contributing to sex drive and also are converted to estrogen in peripheral tissues. After menopause, when the ovaries stop producing estrogens this conversion of adrenal androgens is the source of estrogen in the body.

Adrenal Medulla Hormones

The medulla has hormone producing cells called chromaffin cells which are controlled directly by the autonomic nervous system (ANS) to secrete hormones. Because of this direct nervous system control the release of hormones can happen very quickly.

The 2 principal hormones secreted in the adrenal glands are epinephrine and norepinephrine sometimes called adrenaline and noradrenaline respectively.  Both these hormones are sympathomimetic and are largely responsible for what is known as the “Fight or flight response”

These hormones also help the body to resist stress and have many effects on the body the basic ones are:

1.   They increase heart rate and force of contraction increasing blood pressure

2.   Increase blood flow to the heart, liver, skeletal muscle and adipose tissue.

3.   Dilate the airways to the lung

4.   Increase the levels of blood glucose and fatty acids

If you look at the list above you can see how it would prepare the body to either fight or flight from a stressor – think coming across a tiger on your morning walk – do you stay and fight or run?

It is clear that the adrenal glands although small are a very important part of the system that keeps us functioning well and happy. It contributes to the fundamental function of maintain blood pH through aldosterone and our ability to manage stress.

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