Adrenal gland

The adrenal gland or supra renal gland is composed of an outer
cortex and an inner medulla. The adrenal cortex forms the major portion of
the total mass of tissue of adrenal gland. In adults three concentric zones are
discernible within the cortex. 1. A thin outer most layer, the Zona
glomerulosa, 2. A thick middle region, Zona fasciculata and 3. A
relatively thick inner layer, the Zona reticularis.

In man, the cells of zona fasciculata and zona reticularis act as a single unit, the main function of which is to form glucocorticoids and to a lesser extent androgens and possibly oestrogens. The mineralocorticoid hormone, aldosterone is secreted by the cells of the zona glomerulosa. The enzymes necessary for its synthesis reside in the cells of the zona glomerulosa. All the adreno corticoid hormones are
steroids. (adrenal gland)

Action of glucocorticoids

The major glucocorticoids are cortisone and certain closely related
steroids. These hormones stimulate the production of glucose from
non-carbohydrate sources such as fats and amino acids. Glucocorticoids
also decrease glucose utilization by tissues in general. All these effects lead
to increased blood glucose level. Cortisone also acts as an anti-inflammatory
agent. (adrenal gland)

Action of mineralocorticoids

The major effect is on the metabolism of sodium ions and indirectly
potassium ions. The major mineralocorticoid hormone is Aldosterone. Its
most important effect is to promote the resorption of sodium ions from the
renal glomerular filtrate. Secondary effects of sodium retention are an
increased chloride retention and a decreased potassium retention by the
kidneys. The most important function of the adrenal cortex is its role in stress
tolerance. (adrenal gland)

Adrenal medulla

The medulla of adrenal gland differs both in morphology and
physiology from the cortex portion. Both cortex and medulla are derived
independently and from totally different tissues in the embryo. The adrenal
medulla in the adult humans and other mammals is invested closely by the
cortical tissue.

The cells of the adrenal medulla are large ovoid and columnar
in type and are grouped into clumps around the blood vessels. The
hormones produced by adrenal medulla are 1. Adrenalin or epinephrine
and 2. Nor adrenalin or nor epinephrine. The two hormones belong to a
group called catecholamines. The various physiological and biochemical
actions of adrenalin or epinephrine are the following: (adrenal gland)

1. Adrenalin stimulates constriction of blood vessels supplying the intestine,
kidneys, viscera and skin and causes dilation of blood vessels supplying
skeletal and heart muscle.

2. It increases the rate, amplitude and frequency of the heart beat.
3. It causes relaxation of the smooth muscles of the digestive tract and brings
peristalsis to a halt
4. It causes relaxation of the bronchi, dilation of the pupil, closure of
sphincters and increases sweating
5. It causes contraction of muscles associated with hair follicles and makes
the hair “stand on end” and causes goose flesh
6. It accelerates respiration and stimulates mental alertness
7. It stimulates the breakdown of glycogen to glucose, thereby increasing
oxygen consumption and heat production.
8. Biochemically it releases the free fatty acids and increases blood glucose
level.
9. Adrenalin prepares an individual during emergency or stress situations.
Hence it is called the fight, flight and fright hormone.

Action of Nor adrenalin or Nor epinephrine

Nor adrenalin has certain effects similar to that of adrenalin. For
example, both the hormones dilate the coronary vessels. However, nor
epinephrine cause vaso constriction in most organs other than heart.

It increases both the systolic and diastolic blood pressures. It exerts a weakly
inhibitory action upon the contractile activity of smooth muscle in the gastro
intestinal tract. However, it does not relax the smooth musculature of the
pulmonary bronchioles. Nor epinephrine exerts very little effect upon
carbohydrate metabolism and oxygen consumption. (adrenal gland)

Adrenal gland

Action of glucocorticoids

Action of mineralocorticoids

Adrenal medulla

Action of Nor adrenalin or Nor epinephrine

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