7C renal system applications

What 3 hormones control reabsorption & secretion?

RAAS, ADH, ANP

RAAS

Aldosterone causes reabsorption of Na & Cl & secretion of K in the collecting duct

ADH

Increases permeability to water in cells of the distal tubule & collecting duct -> higher water reabsorption

ANP

Decreases Na & water reabsorption, inhibits aldosterone & ADH release

Renin-angiotensin pathway

Dehydrated/Na+ deficiency/hemorrhage -> decrease in BV & BP -> increased renin -> increaed angiotensin I -> ACE -> increased angiotensin II -> adrenal cortex -> increased aldosterone -> increased Na+ & water reabsorption in kidneys -> increase BV & BP

What happens for urine to become more concentrated?

1. symporters in thick ascending limb establish an osmotic gradient

2. principal cells in collecting duct reabsorb more water when ADH is present

3. urea recycling causes buildup of urea in the renal medulla

How does your body/kidneys respond to dehydration?

1. decreased flow of saliva -> dry mouth & pharynx

2. increased blood osmolarity → stimulates osmoreceptors in hypothalamus

3. decreased BV → decreased BP → increaed renin release → increased angiotensin II formation

ALL will lead to:

stimulates thirst center in hypothalamus → increases thirst → increases water intake → increases body water to normal level & relieves dehydration

What 5 factors maintain body water balance?

Thirst center for hypothalamus, angiotensin II, aldosterone, ANP, ADH/vasopressin

Thirst center in hypothalamus

Stimulates desire to drink fluids

Angiotensin II

Stimulates secretion of aldosterone -> reduces loss of water in urine

Aldosterone

Promotes urinary reabsorption of Na+ & Cl- which increases water reabsorption through osmosis -> reduces water loss in urine

Atrial Natriuretic peptide (ANP)

Promotes natriuresis, elevated urinary excretion of Na+ (and Cl-) accompanied by water -> increases loss of water in urine

ADH/vasopressin

Promotes insertion of water-channel proteins (aquaporin-2) into the apical membranes of principal cells in the collecting ducts of the kidneys -> water permeability of these cells increases -> more water is reabsorbed -> reduces loss of water in urine

How does your body (& kidneys) respond to salt intake?

Increased release of ANP/decreased formation of angiotensin II/decreased release of aldosterone -> reduced reabsorption of NaCl by kidneys -> decreased blood volume