Proximal Tubular Function and Renal Clearance Flashcards
What 2 processes of the Proximal tubule aid in homeostatis?
Rebasorption of useful substances - movement from tubule lumen to blood
Secretion of less useful substance - from blood to tubule lumen
What is the function of Proximal tubule?
Reclaims useful filtered substances
Most reabsorption occurs here of H2o and Solutes and NA+ transporters
What Na+ transporters are involved with reabsorption of PCT?
Na+ symporters and antiporters
What are Symporters?
2 or more solutes cross membrane in same direction
What are antiporters?
2 or more solute cross membrane in opposite direction
What are Na+ transporters used for?
Energy is derived indirectly from ATP used in 1 active transport
What is Transport Maximum? what is symbol?
Tm - transporters have upper capacity limit in mg/min
What does solute reabsorption drive?
H2o absorption
How does H2O absorption occur?
Via osmosis
What happens with H2O reabsorption in the Proximal tubule?
H2O reabsorbed with solutes = obligatory
What happens with H20 reabsorption in the Collecting duct?
H20 reabsorption needs to be driven = facultative
Where does reabsorption occur from the Lumen into?
Peritubular capillary
How does the Capillary uptake work?
Forces favouring uptake = forces opposing uptake
What do Na transporters achieve in reabsorption?
near 100% reabsorption of organic solutes (glucose, AA) 80-90% Bicarb 65% H20,Na,K 50% Cl varies with Ca,Mg,Phosphate
What is the Na/K pump located?
Basolaterally in the kidney
What does the Na-K pump do and use?
Uses ATP to keep intracellular Na low
Drives secondary transport of - Glucose,AA,Bicarb,Chloride
What kinds of substances are secreted?
small and filtered substances
Para-aminohippuric acid
What transport is required for secretion?
Active transport
What happens with Para-amnohippuric acid?
Freely filtered, limited Tm secretion, Not reabsorped, indicator of renal blood flow
What is renal clearance?
Volume of plasma cleared of a substance in a given time
What is renal clearance of x?
filtration of (x) + secretion of (x) - reabsorption of (x)
What is clearance ml/min of?
Urine conc x urine flow / plasma conc
What is Inulin?
A polysaccharide
freely filtered
not reabsorbed or secreted
What can inulin clearance be used to work out?
GFR= Uinulin x V/ P inulin
What is a disadvantage of inulin?
Has to be infused
What is a disadvantage of creatinine?
Is endogenous, no infusion needed, small amount secreted
What is creatinine a by-product of?
Muscle metabolism
When is GFR more accurate?
When subject is at rest
