PHS 3342 Lecture Notes - Lecture 10: Straight Arterioles Of Kidney, Countercurrent Multiplication, Ascending Limb Of Loop Of Henle
28 Apr 2018
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February 16, 2018
Aspects of Renal Water Excretion and Conservation
Juxtamedullary Nephrons Actions
Important in producing concentrated urine
Create an osmotic gradient within the renal medulla that allows the kidney to produce urine of varying concentration
Long nephron loops of juxtamedullary nephrons create the gradient
Countercurrent multiplier: depends on three properties of the nephron loop to establish the osmotic gradient
-Descending limb: water leaves via osmosis
•Permeable to water, but not salt
•Increases osmolality of filtrate - most concentrated at the hairpin turn of the loop of Henle
-Starts at ~300 mOsmol (at the top) and increases to ~1200 mOsmol at the deepest part of the
medullar
-Ascending limb: impermeable to water, but pumps salt out
•Decreases osmolality of filtrate
•Thin ascending limb: passive diffusion
•Thick ascending limb: facilitated diffusion using an Na+/K+ pump
-Fluid flows in the opposite direction (countercurrent) through two adjacent parallel sections of a nephron loop
•Flows down in the descending limb, flows up in the adjacent ascending limb
-NB: energy free - uses osmosis and passive diffusion instead
Vasa recta preserve the gradient by acting as a countercurrent exchanger
-The entire length of the vasa recta is highly permeable to water and solutes
•When descending (as an arteriole) into the medulla, it brings nutrients and oxygen to that region of the kidney
-Water leaves the bloodstream and NaCl and solute goes in
•When ascending (as a venule), water comes into the vasa recta and NaCl and urea goes out
-Decreases osmolality to help pick up metabolic waste and concentrate the urine
-Due to countercurrent exchanges between each section of the vasa recta and its surrounding interstitial fluid, the
blood within the vasa recta remains nearly iso-osmotic to the surrounding fluid
•Osmolality increases going down (in the arteriole; also from 300 mOsmol to 1200 mOsmol)
•Decreases going back up (in the venule)
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Document Summary
Create an osmotic gradient within the renal medulla that allows the kidney to produce urine of varying concentration. Long nephron loops of juxtamedullary nephrons create the gradient. Countercurrent multiplier: depends on three properties of the nephron loop to establish the osmotic gradient. Descending limb: water leaves via osmosis: permeable to water, but not salt, increases osmolality of ltrate - most concentrated at the hairpin turn of the loop of henle. Starts at ~300 mosmol (at the top) and increases to ~1200 mosmol at the deepest part of the medullar. Ascending limb: impermeable to water, but pumps salt out: decreases osmolality of ltrate, thin ascending limb: passive diffusion, thick ascending limb: facilitated diffusion using an na+/k+ pump. Fluid ows in the opposite direction (countercurrent) through two adjacent parallel sections of a nephron loop: flows down in the descending limb, ows up in the adjacent ascending limb. Nb: energy free - uses osmosis and passive diffusion instead.
