Kidney function II Flashcards
What is clearance
The volume of plasma that is cleared of a substance in a particular time
How do you calculate renal clearance?
uv/p where u=conc in urine, v=volume of urine, p=conc in plasma
Why is inulin used experimentally to determine renal clearance?
It is not metabolised
it is not absorbed or secreted
it is freely filtered
it is easily measured
What is used clinically to determine renal clearance
Creatinine, although it gives a slight overestimate as some is secreted.
Describe the physiology of Na+ reabsorption in the proximal tubule of the nephron
Na+ is pumped in to the cell from the lumen of the nephron by Na+:H+ Exchanger Isoform 3 (NHE3) in exchange for H+ which is pumped into the lumen.
Na+ is also brought into the cell from the lumen along with an organic ion by the Na+-nutrient symporter.
Na+ then moved into interstitial space by Na+:K+ ATPase pump, and a Na+:HCO3- symporter moves both ions from cell into interstitial space. There is a channel for the K+ to diffuse back into the interstitial space.
There is also a channel through which the organic ion can move into the interstitial space.
There is also paracellular movement of chloride ions from lumen to interstitial space.
Describe the physiology of Na+ reabsorption in the thick ascending limb of the loop of henle
There is Na+:K+:Cl- co-transporter that brings in ions from the lumen into the cell. There is a channel in the apical membrane that allows the flow of K+ back into the lumen.
There is a Na+:K+ ATPase pump moving K+ into the cell and Na+ out. There is a K+:Cl- co-transporter also in the basolateral membrane that allows the flow of K+ back into the interstitial membrane, and a Cl- channel too to maintain the Cl- gradient.
Describe the physiology of Na+ reabsorption in the distal tubule of the LOH
There is a Na+:Cl- co-transporter in the apical membrane bringing the ions into the cell from the lumen.
There is a Na+:K+ ATPase pump in the basolateral membrane that brings Na into the interstitial space and K+ into the cell.
The K+ in the cell and the Cl- can leave the cell into the interstitial fluid via ion channels.
There is also paracellular movement of Cl- from the lumen to the interstitial space
What are the two types of cell in the collecting duct of the nephron and what do they do?
Principle cells which are involved in Na+ uptake
Intercalated cells which are involved in H+ uptake
Describe the physiology of Na+ reabsorption in the principle cells of the collecting duct
There is a sodium channel in the apical membrane that brings Na+ into the cell; then there is a Na+:K+ ATPase pump that moves Na+ into the interstitial fluid and K+ into the cell.
Then at either membrane there is a K+ channel to maintain the K+ gradient pumping K+ out of the cell. There is paracellular movt of chloride ions from the lumen of the collecting duct into the interstitial space.
Describe the physiology of how ADH effects permeability of the walls of the collecting duct to water
ADH acts on the V2 receptor (GPCR), the G protein activated adenylyl cyclase which produces cAMP, which activates PKA, causing AQP 2 channels to go to the membrane.
Water enters the cell via AQP 2 channels and leaves to go into interstitial fluid vis AQP 3,4 channels.
How is Na reabsorbed in different parts of the nephron
PCT = active descending limb = none thin ascending limb = passive thick ascending limb = active DCT = active CD = active
Describe the Na+ reabsorption in the different cells in the collecting duct
Principle cells = Na+ transport
Intercalated cells = H+ transport
What does each of the limbs of the loop of henle do
ascending limb is solute pumping via Na+:K+:2Cl- cotransporter
descending limb is water reabsorption
What cotransporter is present in the ascending limb of the LOH
Na+:K+:2Cl- cotransporter
What AQP are present in the descending limb of the LOH
AQP1, salt also drawn in
