The adrenal glands are situated on the cranial surface of the kidneys (see diagram 16.6). There are two parts to this endocrine gland, an outer cortex and an inner medulla.
Diagram 16.6 - The adrenal glands
The adrenal cortex produces several hormones. These include:
- 1. Aldosterone that regulates the concentration of sodium and potassium in the blood by controlling the amounts that are secreted or reabsorbed in the kidney tubules.
- 2. Cortisone and hydrocortisone (cortisol) that have complex effects on glucose, protein and fat metabolism. In general they increase metabolism. They are also often administered to animals to counteract allergies and for treating arthritic and rheumatic conditions. However, prolonged use should be avoided if possible as they can increase weight and reduce the ability to heal.
- 3. Male and female sex hormones similar to those secreted by the ovaries and testes.
The hormones secreted by the adrenal cortex also play a part in “general adaptation syndrome” which occurs in situations of prolonged stress.
The adrenal medulla secretes adrenalin (also called epinephrine). Adrenalin is responsible for the so-called flight fight, fright response that prepares the animal for emergencies. Faced with a perilous situation the animal needs to either fight or make a rapid escape. To do either requires instant energy, particularly in the skeletal muscles. Adrenaline increases the amount of blood reaching them by causing their blood vessels to dilate and the heart to beat faster. An increased rate of breathing increases the amount of oxygen in the blood and glucose is released from the liver to provide the fuel for energy production. Sweating increases to keep the muscles cool and the pupils of the eye dilate so the animal has a wide field of view. Functions like digestion and urine production that are not critical to immediate survival slow down as blood vessels to these parts constrict.
Note that the effects of adrenalin are similar to those of the sympathetic nervous system.