The posterior pituitary releases vasopressin in response to reductions in blood plasma volume, increases in blood osmolality, and in response to cholecystokinin (CCK) secretion by the small intestine. Vasopressin increases the body's retention of water by increasing the permeability of the distal tubule and collecting ducts. This increases blood volume and blood pressure.
Vasopressin also induces moderate vasoconstriction at high concentrations.
The adrenal cortex of the adrenal gland releases aldosterone in response to a variety of stimuli. Angiotensin II, part of the renin-angiotensin system, triggers aldosterone release. Carotid artery receptors can detect plasma concentration changes of potassium and baroreceptors in vessel walls can detect arterial pressure changes.
Aldosterone upregulates Na+/K+ pumps in the distal tubule and collecting duct of the nephron, resulting in more reabsorption of sodium (with water following osmotically) into the blood and secretion of potassium into urine.
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