Adrenal Gland:
– Each adrenal gland composed of the medulla & cortex
– Adrenal medulla is under control of the sympathetic nervous system & secretes
epinephrine & norepinephrine
– Adrenal cortex secretes:
1) Mineralocortiocids (aldosterone); affects the electrolytes of ECF, Na & K
2) Glucocorticoids (cortisol), increase glucose concentration & affect protein & fat
metabolism
3) Androgenic hormone
Adrenal cortex:
– Adrenocotical hormones are steroids derived from cholesterol
– 80% of cholesterol used for steroid synthesis are provided by LDL in circulating plasma
– Has 3 distinct area:
1. Zona glumerulosa:
o 15% of adrenal cortex
o Thin layer of cells
o Secretes aldosterone; because it contains enzyme aldosterone synthase
o Secretion controlled by the ECF concentration of angiotensin II & K+
2. Zona fasiculata:
o 75% of adrenal cortex
o Middle layer
o Secretes: glucocortiocoids, cortisol & corticosterone & small amounts of adrenal
androgens & estroegns
o Secretion controlled by the hypothalamic-pituitary axis via adrenocorticotropic hormone
(ACTH)
3. Zona Reticularis:
o Deepest layer of the cortex
o Secrete adrenal androgens dehydroepiandrosterone (DHEA) & small amounts of
estrogens & glucocorticoids
o Secretion controlled by ACTH & cortical androgen-stimulating hormone, released from
the pituitary gland
– 90-95% of cortisol in plasma binds to protein; especially to transcortin
“cortisol-binding globulin” & to albumin
– Cortisol has a long half-life 60-90 minutes; due to high degree of protein binding
– Adrenal steroids hormones are degraded mainly in the liver & conjugated to glucuronic
acid & to sulfate (25% excreted in bile & then in feces & remaining in urine)
– Angiotensin II → increase output of aldosterone; leading to hypertrophy of Zona
glumerulosa
– ACTH → increase secretion of cortisol & adrenal androgens → hypertrophy of Zona
Fasiculata & Zona reticularis
– Normal concentration of aldosterone in the blood is 6 ng/100ml
– Cocnetration of cortisol is 12μg/100ml
Function of the mineralocorticods-aldosterone:
1) Aldosterone deficiency causes severe renal sodium chloride wasting & hyperkalemia
(death in 2-3 days by total loss)
2) Increase renal tubular reabsorption of sodium & secretion of potassium
3) Excess aldosterone increase extracellular fluid volume & arterial pressure
4) Excess aldosterone causes hypokalemia & muscle weakness
5) Little aldosterone causes hyperkalemia & cardiac toxicity:
o Increased serum K concentration
o Weakness of heart contraction
o Development of arrhythmia
o Heart failure
6) Excess aldosterone increases tubular hydrogen ion secretion & causes mild alkalosis
7) Aldosterone stimulates sodium & potassium transport in sweat gland, salivary gland &
intestinal epithelial cells
Regulation of aldosterone secretion:
1. Concentration of ECF
2. Extracellular fluid volume
3. Blood volume
4. Blood pressure
5. Increased or decreased K ion concentration
6. Increased level of II
