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They are paired in and have clear cut cortical & medullary tissue. Located close to the kidneys and hence the name ‘Ad-Renal’. They are highly vascularized. For endocrinological purposes, the adrenal can be divided into two parts: Adrenal Medulla and Adrenal Cortex. Adrenal Medulla
It differentiates from neural crest cells of ectodermal layer. The cells are modified ganglion cells and have the granules that take stain so called chromaffin tissue. Adrenal medulla is functional part of nervous system and is a bridge between nervous & endocrine system just like posterior pituitary. Adrenal medulla is having two zones: One outer which primarily secretes epinephrine and another inner zone that secretes nor-epinephrine. Both these hormones are collectively called as Catecholamines. The stimulus for their section is acetyl choline by preganglionic sympathetic nerve terminals.
Functions of adrenaline and nor adrenaline : Both adrenal medullary hormones perform similar actions on various target organs that are listed below:
- Cardiovascular system – increase in heart rate, blood circulation, rise in blood pressure and more blood flow through myocardium and brain.
- Respiratory system- dilatation of bronchioles and increase in tidal volume.
- Liver- breaks down of glycogen and rise in blood glucose concentration.
- Spleen- contraction of spleen and thus increase in number of RBCs in blood.
- Digestive system- decrease in digestion enzymes and movement of food.
- Skin- erection of hair (pilo erection).
- Eye- Dilatation of pupil so improved vision.
Adrenal Cortex:
Adrenal cortex is composed of three zones, the Zona Glomerulosa (outer most), Zona fasciculate (middle zone) and zona reticularis (inner most). About 50 different steroids are synthesized and secreted from adrenal cortex. Each zone produces three different group of hormones each of which are chemically steroid molecules.
- Zona glomerulosa – Mineralocorticoid hormones
- Zona fasciculata- Glucocorticoid hormones
- Zona reticulata – Adrenal sex steroids
Mineralocorticoids:This group includes Aldosterone hormone (21 carbon, steroid molecule) which acts on distal renal tubule and brings about sodium reabsorption from tubular fluid and more excretion of potassium. The hormone is released in situations like sodium deficiency, dehydration, blood loss due to injuries etc.
Glucocorticoids:This group includes cortisol, cortisone and corticosterone. These hormone acts on various body cells especially liver, kidney, adipose tissues and alters metabolism of carbohydrates, lipids and proteins. Main actions are:
- Stimulates synthesis of glucose from non-carbohydrate compounds such as amino acids (process of gluconeogenesis).
- Stimulate protein and lipid catabolism (proteolysis & lipolysis).
- Increases blood level of glucose, fatty acids and amino acids.
- Decreases inflammatory reaction and swellings at site of injuries.
- Decreases allergic reaction and immune reactions of body.
- Cause retention of sodium from the kidneys.
- Induce weight loss by decreasing amount of stored lipids and proteins.
Release of glucocorticoids is directly under the influence of ACTH from anterior pituitary which in turn is influenced by cortisol by negative feedback mechanism. ACTH is secreted under stressful conditions like starvation, exercise, blood loss, infections, fear, anxiety, fatigue etc. In 24 hour cycle, the corticosteroids secretion is maximum when day’s activities start (around 9 AM) and minimum during midnight when body activities are least.
Adrenal sex steroids: are same as are produced from gonads like estrogen and progesterone in females and testosterone in males but the quantity is much less than that produced from gonads. When ovaries or testes gets diseased, than adrenal secretion of sex hormones is increased several folds and causes development of abnormal sex characteristics. Tumors of adrenal gland also lead to production of abnormally high quantity of sex steroids and abnormal sexual development.
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