Lecture 35 Unit 5 Flashcards
what do countercurrent mechanisms require
- a countercurrent flow of fluid through a tubule
- as somatic gradient in fluid surrounding tubule
what are the two countercurrent mechanisms
- countercurrent multiplication
- countercurrent exchange
what happens in countercurrent multiplication
process which produces a progressively increasing osmotic gradient in interstitial fluid of renal medulla
what happens in countercurrent exchange
process which enables oxygen to cells of renal medulla without loss of the osmotic gradient in ISF of renal medulla
what are the two main factors that contribute to building the osmotic gradient
- permeability differences
- countercurrent flow
what are the permeability differences
- descending limb of loop of henle is very permeable to water
- thick ascending limb in loop of henle is impermeable to water
- late DCT and CD only permeable to water in presence of ADH
what happens in countercurrent flow
-descending and ascending loop of heel carry tubular fluid in opposite directions
what are the ADH effects on the osmotic gradient
- ADH stimulates Na+/K+/Cl- symporter activity in thick ascending loop of henle
- ADH stimulates facultative reabsorption of water n upper CD
- ADH stimulates water reabsorption and urea recycling in lower CD
what does the ability of ADH to cause excretion of concentrated urine require?
an osmotic gradient of solutes in the ISF of the renal medulla
what are the 3 major solutes involved in the osmotic gradient
Na+, Cl-, urea
what happens in countercurrent multiplication
- symporters in thick ascending limb cells of the loop of henle cause a buildup of Na+ and Cl- in renal medulla
- countercurrent flow through the descending and ascending limbs of the loop of henle establishes an osmotic gradient in the renal medulla
- cells in the CD reabsorb more water and urea
- urea recycling causes a buildup of urea in the renal medulla
where is urea impermeable
thick ascending limb, DCT, and CD
what is countercurrent exchange
process by which solutes and water are exchanged between blood of vasa recta and ISF of renal medulla
what does the vasa recta act as
a countercurrent exchanger
what does the vasa recta do
provides oxygen and nutrients to renal medulla without washing out the osmotic gradient
