3. Mechanisms to Adjust Urine Concentration Flashcards
How is sodium reabsorbed in the TAL? How much is reabsorbed?
Ka,K,2Cl cotransport
35-40%
*there is also a Cl/Na cotransport but not affected by diuretics. Leaky K channels also important here
How is sodium reabsorbed in the early distal convoluted tubule? How much is reabsorbed?
Na,Cl cotransport
5-8%
How is sodium reabsorbed in the LDCT and CD? How much is reabsorbed?
Luminal Na membrane channel
2-3%
What is the luminal potential in the Proximal tubule?
+/- 2 mV
What is the luminal potential in the TAL? why?
+6 to +10 mV because of K leak channels and tight junctions dont allow Cl through and electroneutrallity is more difficult to maintain
What is the luminal potential in the Distal tubule? why?
-70 mV
Cl is left behind
The descending limb of henle is freely permeable to ______ and impermeable to ______
Water
Na,Cl
What is the thick ascending limb permeable and not permeable to?
Permeable to Na/K/2Cl through active cotransport
ALWAYS impermeable to water
What part of the nephron is considered the diluting segment?
Thick segment, it dilutes the urine and concentrates the renal medullary interstitium
What drives paracellular reabsorption of K, Ca, and Mg in the TAL?
K leaky channels
Makes the tubular urine + and thus driving the cations to be reabsorbed by paracellular diffusion
Major site for reabsorption of the cations
*there is also a Cl/Na cotransport but not affected by diuretics. Leaky K channels also important here
What is the major site of physiological control of salt and water balance?
Late DCT and collecting duct
What does aldosterone stimulate?
Na reabsorption, K secretion, H secretion in the late DCT and CD
ANP inhibits Na reabsorption where?
medullary collecting duct
ADH stimulates water reabsorption where?
Late DCT and CD
How does aldosterone increase Na reabsorption in principal cells?
Goes to the nucleus and causes proteins to be transcribed and inserted into the principal cell membrane. Incorporation of Na channels in luminal membrane and Na,K ATPase ion pumps in basolateral membrane. Sodium comes in and K is exchanged to maintain electroneutrallity
How does ADH increase water permeability ?
In late distal tubule and collecting duct, it attaches to V2 receptors and inserts aquaporin channels on the tubular lumen side
What part of the kidney has the highest solute concentration? why?
Inner medulla
Because of low blood flow
The countercurrent multiplier mechanism requires integrated function of what 3 components?
Descending, ascending limbs of henle loop
Vasa recta capillaries
Collecting ducts
Why is the countercurrent multiplier mechanism important?
It allows us to concentrate solute in medullary interstitium to pull water out of tubular. Enables kidneys to excrete highly concentrated urine, and conserve water during periods of dehydration
How is sodium reabsorbed in the proximal tubule? How much is reabsorbed?
Cotransport with glucose, amino acids, phosphates
Antiporter with H
50-55%
How does the medullary interstitium become hyperosmolar?
Na gradient that the Na,K, Cl cotransporter establishes in TAL
The countercurrent multiplier mechanism is augmented by action of what?
ADH in CD
What increases the BUN/Creatine ratio?
Urea, if we are dehydrated and need to concentrate the urine more, more urea will be reabsorbed in Proximal tubules and under direction of ADH, promote urea from inner medullary collecting duct
Does the vasa recta pull a lot of solutes out of the medullary interstitium?
No, the slow flow allows for most of the solutes to remain in the interstitium to help concentrate the urine. They do not disturb the high concentration
