Hormonal Regulation

Antidiuretic Hormone (ADH)

• Stored in the posterior pituitary gland
• Released in response to changes in blood osmolality (osmolality of blood increases with dehydration and decreases with over hydration)
• Osmoreceptors (in hypothalamus) release ADH when osmolality increases
• Promotes water conservation by acting directly on the renal tubules and collecting ducts to make them more permeable to water
• This causes water to return to systemic circulation, which dilutes the blood and decreases its osmolality
• Causes a decrease in urine output
• When the blood is diluted again, ADH is no longer secreted and urine output returns to normal
• ADH also stimulates the thirst centre
• Summary: less urine output. Attempts to dilute the blood
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Aldosterone

• Released by adrenal cortex
• Secreted in response to increased plasma potassium OR falling sodium levels OR as part of the renin-angiotensin system to counteract hypovolemia
• To fix hypovolemia, renin is released from the kidneys in response to sympathetic nervous stimulation and decreased renal blood flow
• A cascade of physiological and endocrine responses occur, one of which is to release aldosterone
• Acts on the distal portion of the renal tubule to increase reabsorption (saving) of sodium, and the secretion and excretion of potassium and hydrogen
• Summary: less urine output. Saves sodium, gets rid of potassium and hydrogen
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Natriuretic Peptide

• Released from cardiac muscle cells
• Acts of peripheral vasculature, other hormones, and the kidneys to facilitate diuresis
• Responds to increases in circulating blood volume
• Increase sodium exertion and fluid loss
• Reduces thirst
• Blocks the release of ADH and aldosterone
• Summary: more urine output. Excretes sodium
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