Adrenal Cortex

 The adrenal glands sits at the top of Kidney, hence they are called suprarenal glands

There are 2 adrenal glands, one on each kidneys

The adrenal glands has two parts: outer adrenal cortex and inner adrenal medulla

Adrenal cortex secretes steroid hormones and adrenal medulla secretes catecholamines

Adrenal glands are essential for life

Adrenal cortex has three layers:

1. Zona glomerulosa which secrete mineralocorticoids, eg: aldosterone
2. Zona fasciculata which secret glucocorticoids, eg: cortisol
3. Zona reticularis which secrete sex steroids, eg: androgen, oestrogen and progesterone.

Adrenal medulla secretes:

• Epinephrine
• Nor-epinephrine
• Dopamine

Regulation of glucocorticoid secretion is done by ACTH (Adrenocorticotrophic Hormone)

• Hypothalamus release CRH (Corticotropin Releasing Hormone) which stimulates anterior pituitary to secrete ACTH via hypothalamo-hypophysial portal system

Factors affecting ACTH secretion

• Diurnal variation of ACTH secretion/circadian rhythm
• Response to stress

Actions of Glucocorticoids

On protein metabolism

• Causes breakdown of proteins in skeletal muscles

On carbohydrate metabolism

• Increases glucose fomation in the liver
• Prevent peripheral utilization of glucose causing increase in blood glucose level
• Increases glycogen synthesis

On fat metabolism

• Favours mobilization of fatty acids from adipose tissue

On electrolyte and water metabolism

• Increases retention of sodium and excretion of potassium by kidneys

Vascular reactivity

• Sensitizes arterioles to constrictor actions of catecholamines
• Maintains blood pressure

Anti-inflammatory and Anti-allergic action

High doses causes

• Decreased local reaction
• Prevents tissue damage
• Decreased fibroblastic activity
• Reduces histamine induced features of allergy

Cushing’s syndrome

It is a clinical disorder which results from excess secretion of glucocorticoids

Characteristic features

• Growth retardation in childhood due to early fusion of epiphysis
• Facial features: Moon like face, Hirsutism, Acne & pigmentation
• Centripetal distribution of fat: Thin extremity, pendular abdomen, Buffalo hump
• Purple striae due to thinning and stretching of skin

Actions of Mineralocorticoids (Aldosterone)

• Causes retention of sodium and increased urinary excretion of potassium
• By stimulating sodium reabsorption, aldosterone causes water retention resulting in expansion of extracellular fluid volume

Regulation of aldosterone secretion

• Decrease in plasma sodium increases aldosterone secretion via renin-angiotensin-aldosterone system
• Circadian rhythm

Applied Aspects: Addison’s disease

• Decrease in secretion of mineralocorticoids leads to Addison’s disease

Symptoms are:

• Hypotension
• Anorexia, nausea, vomiting, diarrhea leading to dehydration and weight loss
• Muscular weakness, mental confusion
• Decreased ability to withstand stress due to trauma, infection

Sex hormones

• At puberty adrenal glands secrete sex hormones, testosterone in males, estrogen and progesterone in females
• It contributes to increase in the muscle mass, sexual hair, pimples etc.
• It secretion is regulated by ACTH