Kidney Function 2 Flashcards
Where is water reabsorbed in the nephron?
across the whole nephron but primarily in the proximal tubule
What hormone regulates water reabsorption?
ADH
Where is sodium reabsorbed in the nephron?
across the whole nephron but primarily in the proximal tubule
What hormone regulates sodium reabsorption?
aldosterone
Which ion is secreted in the nephron?
potassium
What percentage of potassium is excreted?
10%
What hormones regulate calcium retention?
parathyroid hormone and vitamin D3
How is phosphate reabsorbed?
cotransport with sodium in the proximal tubule
How is glucose reabsorbed?
cotransport with sodium in the proximal tubule
What percentage of glucose is reabsorbed?
100%
How are amino acids reabsorbed?
cotransported with sodium in the proximal tubule via 7 different transporters
What percentage of creatinine is excreted?
100%
What percentage of urea is excreted?
50%
What is the concentration of the fluid in the cortex?
300mOsm - isotonic with plasma
What is the concentration of filtrate at the base of the medulla?
1200mOsm
What is the function of the proximal tubule?
Does the majority of reabsorption of water, sodium and other solutes
What is the function of the descending limb of the loop of Henle?
It is impermeable to solutes but water permeable - so only water reabsorption will occur - water will be reabsorbed to equilibrate osmotically with the interstitial fluid
What is the function of the ascending limb of the loop of Henle?
sodium reabsorption - at first passive reabsorption then active
What is the osmolarity at the end of the loop of Henle?
100mOsm
What is the variation in osmolarity at the end of the collecting duct?
50-1200mOsm
Where do ADH and aldosterone act?
in the collecting duct
What is the action of ADH?
inserts aquaporins into the collecting duct to increase water permeability so the water will be reabsorbed to equilibrate with the extracellular fluid
What drives sodium reabsorption in the tubules?
Na+/K+ ATPase on the basolateral membrane
What drives anion reabsorption in the tubules?
follows the electrochemical gradient
How do anions move?
trancellularly and paracellularly
What drives water reabsorption in the tubules?
moves by osmosis - follows solutes
How does water move?
transcellularly and paracellularly
What drives reabsorption of K+, Ca2+ and urea?
solvent drag - paracellular
How is sodium reabsorbed in the proximal tubule?
sodium goes across the apical membrane passively via cotransporters and exchangers (with H+) and then goes across the basolateral membrane via the Na+/K+ ATPase - however there is also some paracellular movement particularly in the late proximal tubule
How is HCO3- reabsorbed in the proximal tubule?
the Na+/H+ exchanger leads to HCO3- being reabsorbed
How is Cl- reabsorbed in the proximal tubule?
both transcellularly and paracellularly - paracellular is dominant at first and then becomes transcellular
How is sodium reabsorbed in the thin ascending limb of the loop of Henle?
paracellularly - due to concentration gradient
How is sodium reabsorbed in the thick ascending limb of the loop of Henle?
Both transcellular and paracellular. Transcellular involves the Na+/K+/2Cl- cotransporter and also a Na+/H+ exchanger - it is then moved across the basolateral surface via the Na+/K+ ATPase
What is the action of frusemide?
inhibits sodium potassium chloride cotransporter in the loop of henle (loop diuretic)
Why is water not reabsorbed with the solutes in the thick ascending limb?
because the cell junctions are water tight
How is Na+ reabsorbed in the distal tubule?
Entirely transcellular - apical via a Na/Cl cotransporter and basolateral via Na+/K+ ATPase. There is no paracellular route.
What is the action of thiazide diuretics?
Block the Na/Cl cotransporter in the distal tubule
How is sodium reabsorbed in the collecting duct?
At the apical membrane it is transported by sodium channels while there is potassium secretion in the opposite direction by potassium channels. At the basolateral membrane there is Na+/K+ ATPase
How are endogenous organic acids absorbed?
Na dependent cotransporters on the apical membrane and H+ dependent cotransporters or organic anion exchangers on the basolateral membrane
How are exogenous organic acids excreted?
organic anion exchanger
What is the countercurrent mechanism?
The way that a gradient of increasing osmolarity is produced along the medullary pyramids. The loops of Henle are countercurrent multipliers and the vasa recta are countercurrent exchangers. Need the gradient in order to be able to concentrate urine. It is inhibited by loop diuretics.
How do you make concentrated urine?
With ADH - add aquaporins to the membrane in the collecting duct so water comes out - however you need the concentration gradient
