12. Urine Concentration and Dilution Flashcards
What is the range of dilution the kidney can make the urine? Yes
Kidney can generate a urine as dilute as 40mOsm (1/7 plasma osmolality) or as concentrated as 1200mOsm (4 times plasma osmolality)
Depends on water intake
Slides 28-31 Nov 26
What is the difference between the descending and ascending loop of Henle?
Descending limb- passively permeable to water, not to NaCl
Filtrate concentrates in the medulla
Ascending limb- active transport of Na, Cl follows passively; impermeable to water
Concentrate the interstitial fluid in medulla
Dilute the ultrafiltrate
Slide 32-33 Nov 26
What is the countercurrent multiplier system?
Positive feedback loop
The more transport by ascending limb, the more concentrated the descending limb fluid is
Facilitated transport by ascending limb
Slide 34 Nov 26
What does urea assist in?
What is the urea?
Urea assists in increased medullary hyperosmolality
Nearly half the solute in the interstitial space is urea
A product of protein metabolism, contributes greatly to hyperosmotic interstium in a high protein diet
Urea transporters in loop of Henle and distal neuron
AVP allows urea to readily leave the distal nephron creating a urea recycling loop
Slide 35 Nov 26
What are the vasa recta and their functions?
Blood vessels in kidney
Countercurrent exchange maintain osmotic gradient in the medulla
Draws excess water and solutes
Vasa rectas counter current exchanger & low blood flow minimize washout if medullary hypertonicity
Slides 36-37 nov 26
Why does the vasa recta have a hairpin turn?
It creates a counter current exchanger
As isosmotic blood flows into medulla, it loses H2O & gains solutes in descending loop, the hyperosmotic blood then loses solutes and gains H2O as blood travels up the ascending loop
Slide 37 Nov 26
What are loop diuretics used for?
Used to treat edema associated with heart failure, hepatic cirrhosis, renal impairment, nephrotic syndrome
Hypertension, cerebral/pulmonary edema where rapid diuresis is required
Acts on the NKCC2 in the apical membrane of the thick ascending loop of Henle
Prevents generation of a hypertonic medulla, removing the osmotic driving force for H2O in the distal nephron resulting in an increase in urine secretion
Blocks reabsorption of fluid by the loop of Henle
Slide 38 Nov 26
How is osmotic pressure of urine modulated?
What is antidiuresis and diuresis?
Modulated by arginine vasopressin Increases: Water permeabilities if the collecting duct NaCl reabsorption in the TAL Urea reabsorption by the IMCD
Antidiuresis- low urine flow
Diuresis- high urine flow
Slide 39 Nov 26
What do kidneys do in the absence of AVP?
They excrete hyposomotic urine (excess H2O)
Increase in plasma osmolality & decrease in circulating blood volume trigger the posterior pituitary to release AVP in order to retain H2O
This triggers the distal regions of the nephron to become permeable to H2O, allowing H2O to flow down the steep osmotic gradient created by the countercurrent multiplier resulting in the excretion of concentrated urine
Slide 41 Nov 26
How does AVP increase water permeability?
AVP binds to V2, G protein coupled receptor
Activated adenylate cyclase pathway resulting in insertion of AQP2 receptors into the apical membrane
PKA phosphorylates unknown protein resulting in AQP2 insertion
Increased transcription of AQP2 channels
Slide 42 Nov 26
