Adrenal glands (The emergency glands)
- Two pyramid-shaped adrenal glands rest on the top of each kidney, hence also called supra-renal glands.
- Each adrenal gland actually consists of two separate endocrine parts; outer cortex and inner medulla.
- They cortex and medulla not only produce different hormones but also have separate target organs.
1. Adrenal cortex:
- It is the outer part of adrenal glands and consists of three distinct layers; zona glomerulosa, zona fasciculata and zona reticularis.
- It accounts for about 90% of the weight of the gland.
- It secretes three classes of general steroid hormones; glucocorticoids, a single mineralocorticoid (aldosterone) and small quantities of gonadocorticoids (sex hormones) which are essential to life.
Glucocorticoids:
- They consist of cortisol and corticosterone (secreted by zona fasciculata and zona reticularis).
- Glucocorticoids regulate carbohydrate metabolism by increasing glycogenesis (formation of glycogen from glucose, and gluconeogenesis (synthesis of glucose in liver by non-carbohydrate substances like amino acids and fats).
- They also suppress allergic reactions and inflammatory responses.
- They also affect growth and decrease the effects of physical and emotional stress.
Mineralocorticoids:
- They are produced by zona granulosa and are a group of steroid hormones.
- The major mineralocorticoid (aldosterone) increases blood sodium (by reabsorption of sodium from sweat, saliva and gastric juice) but decreases potassium in blood.
- The main target area of aldosterone is the kidney.
Gonadocorticoids (sex hormones):
- These sex hormones have only a slight effect on the sex organs or gonads.
- They consist mainly of weak male hormones called androgens and lesser amount of female hormones called estrogens.
- They are secreted by the cells in zona fasciculata and perhaps in the zona reticularis.
- Disorders of the adrenal gland can cause masculine characteristics in female such as facial hair, deep voice, reduction in breast size, and development of breasts in males (gynecomastia).
Hyperadrenalism (over activity of the adrenal cortex) leads to Cushing’s disease and adrenogenital syndrome.
- Symptoms of Cushing’s disease include fattening of face, chest and abdomen accompanied by abdominal striations, weak muscles etc.
- Adrenogenital syndrome in females include appearance of male characteristics like beard, moustaches, male voice etc. and accelerated sexual development in males.
Hypoadrenalism (underactivity of adrenal cortex) produces Addison’s disease whose symptoms include anemia, weakness and fatigue, increased blood potassium and decreased blood sodium, bronzed skin color etc.
2.Adrenal medulla:
- It is the inner portion of the adrenal glands and is not essential to life.
- Granules in the cells of adrenal medulla secrete and store two hormones; epinephrine (adrenaline) and nor-epinephrine (nor-adrenaline).
- These hormones produce effects similar to stimulation by the sympathetic nervous system.
- Ephinephrine or adrenaline is secreted in much larger amount at the time of emergency (flight, fright, fight), hence also called an emergency hormone.
- It increases the rate of metabolism and the cardiac output, dilates blood vessels, increases respiratory rate, increases the blood pressure etc.
- Nor-epinephrine or nor-adrenaline is secreted in much smaller amount and has lesser effects.
- It dilates the pupil of the eye, increases the activity of the heart, regulates the blood pressure, enhances lipid metabolism and relaxes the smooth muscle of the gastrointestinal tract.