CHP 6 (155-156)
Adrenal glands are located above the kidneys (suprarenal glands).
Consists of a cortex (80% of the total mass), and a medulla.
It is essentially two glands in one because the cortex and medulla are structurally and functionally distinct.
The adrenal cortex is stratified into 3 distinct layers: 1) zona glomerulosa (outer layer), 2) zona fasciculata
(middle layer), 3) zona reticularis (inner layer).
The adrenal cortex secretes a number of hormones collectively called adrenocorticoids:
o Mineralcorticoids: primarily aldosterone; secreted exclusively by cells in the zona glomerulosa. They
regulate Na reabsorption and K secretion by the kidneys.
o Glucocorticoids: primarily cortisol; secreted by cells in the zona fasciculate and zona reticularis. They
regulate body’s response to stress; protein, carbohydrate, and lipid metabolism; blood glucose levels.
o Sex hormones: primarily androgens; secreted by zona fasciculate and zona reticularis, and by the
gonads. They regulate reproductive function. Secretion of these in the adrenal cortex is very little. In
females, adrenal androgens may stimulate sex drive.
Adrenal medulla contains chromaffin cells and secretes catecholamines. 80% is epinephrine, 20% is
norepinephrine, 1% is dopamine. Epinephrine is released during times of stress or excitation. It increases the
heart rate and mobilization of energy stores.
CHP 19 (548-550)
THE EFFECTS OF ALDOSTERONE
Aldosterone is a steroid hormone released from the adrenal cortex that regulates both the reabsorption of Na
and the secretion of K.
Aldosterone binds to cytosolic receptors in the principal cells of late distal tubules and collecting ducts.
It increases the number of open Na/K channels in the apical membrane, by causing existing channels to open
and synthesizing new ones. Increasing the concentration of Na/K pumps in the basolateral membrane.
Controls Na reabsorption through the renin-angiotensin aldosterone system (RAAS).
THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM
o Within the walls of the afferent artieole are granular cells that secrete renin ( a proteolytic enzyme).
o Macula densa cells detect changes in the Na and Cl concentrations in the tubular fluid. when [Na]
decreases, renin secretion increases.
o Renin acts on angiotensinogen which is secreted by the liver. It converts it to anginotensin I.
o As anginotensin I circulate in the bloodstream, they encounter anginotensin converting enzyme (ACE),
which is bound to the inner surfaces of capillaries. ACE converts it to anginotensin II.
o Anginotensin is a vasoconstrictor (maintains MAP), and stimulates aldosterone release from the adrenal
cortex. Also acts on the hypothalamus to stimulate ADH release and thirst.
Summary of anginotensin II to increase MAP:
1. Anginotensin II stimulates vasoconstriction of systemnic arterioles, increasing MAP.
2. It stimulates the adrenal cortex to secrete aldosterone, increasing Na reabsorption and water
reabsorption to increase.
3. It stimulates posterior pituitary to secrete ADH, increasing water reabsorption, minimizing fluid loss,
and maintaining plasma volumes, thereby maintaining MAP.
4. It activates hypothalamic neurons to stimulate thirst and fluid intake, increasing plasma volume,
thereby increasing MAP.
Decrease in blood pressure is a primary stimulus for renin release.