table 26.4 hormonal regulation of tubular reabsorption and tubular secretion

hormones

angiotensin II

aldosterone

antidiuretic hormone ADH

atrial natriuretic peptide ANP

parathyroid hormone PTH

angiotensin II major stimuli that trigger release

low blood volume or low blood pressure stimulates renin-induced production of angiotensin II

angiotensin II mechanism and site of action

stimulates activity of Na+-H+ antiporters in proximal tubule cells

angiotensin II effects

increases reabsorption of Na+ and water, which increases blood volume and blood pressure

aldosterone major stimuli that trigger release

increased angiotensin II level and increased level of plasma K+ promote release of aldosterone by adrenal cortex

aldosterone mechanism and site of action

enhances activity of sodium-potassium pumps in basolateral membrane and Na+ channels in apical membrane of principal cells in collecting duct

aldosterone effects

increases secretion of K+ and reabsorption of Na+

increases reabsorption of water, which increases blood volume and blood pressure

antidiuretic hormone adh major stimuli that trigger release

increased osmolarity of extracellular fluid or decreased blood volume promotes release of adh from posterior pituitary gland

adh mechanism and site of action

stimulates insertion of water channel proteins (aquaporin-2) into apical membranes of principal cells

adh effects

increases facultative reabsorption of water, which decreases osmolarity of body fluids

atrial natriuretic peptide anp major stimuli that trigger release

stretching of heart atria stimulates anp secretion

anp mechanism and site of action

suppresses reabsorption of Na+ and water in proximal tube and collecting duct

inhibits secretion of aldosterone and adh

anp effects

increases excretion of Na+ in urine (natriuresis)

increases urine output (diuresis) and thus decreases blood volume and blood pressure

parathyroid hormone pth major stimuli that trigger release

decreased level of plasma Ca2+ promotes release of PTH from parathyroid glands

pth mechanism and site of action

stimulates opening of Ca2+ channels in apical membranes of early distal tubule cells

pth effects

increases reabsorption of Ca2+