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The Adrenal Glands

The adrenal glands are two small structures situated one atop each kidney.

Both in anatomy and in function, they consist of two distinct regions:
Link to graphic showing the location and structure of the adrenal glands (92K).

The Adrenal Cortex

Using cholesterol as the starting material, the cells of the adrenal cortex secrete a variety of steroid hormones. These fall into three classes:

Production of all three classes is triggered by the secretion of ACTH from the anterior lobe of the pituitary.

These hormones achieve their effects by:
Discussion of mechanism

Glucocorticoids

The glucocorticoids get their name from their effect of raising the level of blood sugar (glucose). One way they do this is by stimulating gluconeogenesis in the liver: the conversion of fat and protein into intermediate metabolites that are ultimately converted into glucose.

The most abundant glucocorticoid is cortisol (also called hydrocortisone).

Cortisol and the other glucocorticoids also have a potent anti-inflammatory effect on the body. They depress the immune response, especially cell-mediated immune responses. [Discussion of mechanism]

For this reason glucocorticoids are widely used in therapy:

Mineralocorticoids

The mineralocorticoids get their name from their effect on mineral metabolism. The most important of them is the steroid aldosterone.

Aldosterone acts on the kidney promoting the reabsorption of sodium ions (Na+) into the blood. Water follows the salt and this helps maintain normal blood pressure.
Link to discussion.

Aldosterone also

The secretion of aldosterone is stimulated by:

Androgens

The adrenal cortex secretes precursors to androgens such as testosterone.

In sexually-mature males, this source is so much lower than that of the testes that it is probably of little physiological significance. However, excessive production of adrenal androgens can cause premature puberty in young boys.

In females, the adrenal cortex is a major source of androgens. Their hypersecretion may produce a masculine pattern of body hair and cessation of menstruation.

Addison's Disease: Hyposecretion of the adrenal cortices

Addison's disease has many causes, such as

The essential role of the adrenal hormones means that a deficiency can be life-threatening. Fortunately, replacement therapy with glucocorticoids and mineralocorticoids can permit a normal life.

Cushing's Syndrome: Excessive levels of glucocorticoids

In Cushing's syndrome, the level of glucocorticoids, especially cortisol, is too high.

It can be caused by:

The Adrenal Medulla

The adrenal medulla consists of masses of neurons that are part of the sympathetic branch of the autonomic nervous system. Instead of releasing their neurotransmitters at a synapse, these neurons release them into the blood. Thus, although part of the nervous system, the adrenal medulla functions as an endocrine gland.

The adrenal medulla releases:

Both are derived from the amino acid tyrosine.

Release of adrenaline and noradrenaline is triggered by nervous stimulation in response to physical or mental stress. The hormones bind to adrenergic receptorstransmembrane proteins in the plasma membrane of many cell types.

Some of the effects are: All of these effects prepare the body to take immediate and vigorous action.
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30 May 2014