renal 3 - reabsorbtion & secretion Flashcards
how much fluid is filtered per day? how much of that is excreted?
180L/day but only 1% (1.5L) is excreted
why do we filter so much per day? (2)
to rapidly filter foreign substances
to rapidly regulate ions and water
What drives reabsorbtion at the proximal tubul?
Na+
what is the apical side?
faces the tubule lumen
what side does basolateral face
extracellular fluid
transepitheilial transport
substances cross the apical and basolateral membranes of the tubule cells to enter into the ECF
paracellular transport
susbstances pass through the cell to cell junctions between two adjacent tubule cells
where is active transport found most
Basilateral side and is always active via Na-K-ATPase
keeps Na concentration low in tubule cell, high outdside
how is secondary active transport used in proximal tubule cells?
secondary active transport: smport with Na+
glucose moves in symport with Na+
Passive reabsorbtion
e.g urea nitrogenous waste product
what is urea?
nitrogenous waste product from protein break down
Receptor mediated endocytosis
megalin can bind to proteins & peptides that allow transport via endocytosis. then is digested by lysosmes. (very small amounts of protiens in pee cuz it gets reabsorbed)
Saturation:
the max rate of transport that occurs when all available carriers are occupied (never reach this) TRANSPORT MAXIMUM
If too much glucose filtration exceeds how much you can reabsorb, what will happen?
it will not be reabsorbed since you dont have enough to move it. It will exit in your pee (like diabetes sweeter pee) *called glucosuria
what is the cacluation for excretion
excretion = filtration - reabsorbtion + amount secreted
how do peritubular capillary pressures favor reabsorbtion?
excess plasma protiens draw fulids back into the peritubular capillary. its called osmotic pressure
what is secretion
the transfer of molecules from the extracuelluar fluid into the lumen of the nephron
give an example of secretion of organic solutes, which use (tertiary) active transport
-organic anion transporters: broad range of prodcts transported
aKG-:
a-ketoglutarate is a by-product of the citric acid cycle
what are the steps in secretion?
1 direct active transport
2 secondary indirect active transport
3 tertiary indirect active transfort
4 organic anions enter lumen in exchange for dicarboxylate
what is an OAT trasporter?
uses energy from transporting dicarboxylates down its concentration gradient to move OA- against its concentraion gradient
What is a competitor? what does it have to do with penicillin excretion?
penicilin would be excreted within 3-4 hrs
probenecid is a competitor which is preferentially secreed by the OAT transported, allowing penicillin to stay in the body
