Adrenal glands

There is a pair of adrenal glands, one lying close to the cranial pole of each kidney (Fig. 6.1 I. Each gland has an outer cortex and an inner medulla. There is no con­nection between the two parts and they can be consid­ered as two separate glands.

Adrenal cortex

The hormones produced are known as steroids and have a similar structure based on lipid. There are three groups, each one being secreted by a different layer:

1. Cjlucoeortieoids - secretion is regulated by r∖CTII from the anterior pituitary gland. The hormones are known as Corlieosteroids: the most important are cortisol and corticosterone. In the normal animal they are present in low levels but increase in response to stress. They have two main actions:

- They increase blood glucose levels by reducing glucose uptake by the cells, increasing the conversion of amino acids to glucose in the liver (a process known as gluconeogenesis) and mobilising fatty acids from the adipose tissue ready for conversion to glucose.

- When present in large quantities, they depress the inflammatory reaction, which delays healing and repair. This property is used therapeutically to reduce swelling and inflammation*

Oversecreuon of glucocorticoids, or hyf>erαdrenocαrticαlisjv, leads to symptoms of Cushing's disease.These include polydipsia, polyuria, polyphagia and bilateral symmetrical alopecia.

2. Mineralocorticoids - the most important is aldosterone. This ads on the distal convoluted tubule of the kidney where it regulates acid/base balance of the plasma and ECF by excretion of H* ions and also controls the excretion of Xa’ and K⁺ ions.

T Adrenal sex Iiorniones- both male and female animals produce all types of sex hormones. They are secreted in insignificant quantities, but may be the reason why some animals show a certain level of sexual behaviour despite being neutered.

Adrenal medulla

This produces two hormones with similar actions Adrenaline Iepinephrinel and noradrenaline (norepi­nephrine I. These hormones prepare the body for emergency action, known as the fear, flight, fight" syndrome and are controlled by the sympathetic nervous system. Their actions are to:

1. Raise bkxκl glucose levels by the breakdown of glycogen stored in the liver - t∣h∣cof∣enoh∣sis. This increases the body’s energy levels.

2. Increase the heart rate and the rate and depth of respiration - this increases the amount of oxygen reaching the tissues.

3. Dilate the bld vessels of the skeletal muscles - this enables the supply of glucose and oxygen to reach the areas where it is needed.

4. Decrease the activity of the gastrointestinal tract and the bladder - in an emergency their functions are less important.