Renal 3 Flashcards
Of the 180L/day filtered what is excreted
less than 1% (1.5L)
what does regulated reabsorption allow kidneys to do
selectively return ions and water to plasma and maintain homeostasis
Why filter 180L if only excreting 1%
- rapid way to remove unwanted materials
- rapid regulation of fluid and ions
what can be active and passive
reabsorption
filtrate in lumen and ECF initially have what similar
solute, they are isosmotic
reabsorption involves what two types of transport
transepithilial (transcellular)
paracellular
transepithelial transport
substances cross the apical and basolateral membranes of tubule cells to enter ECF (require protein transporters)
paracellular transport
substances pass through the cell to cell junctions between two adjacent tubule cells
what creates the electrochemical gradient that drives reabsorption
reabsorption of sodium set up by Na-K ATPase
what does sodium do
starts process of active transport that drives all reabsorption within proximal tubule
what kind of transport is basolateral Na always
active transport via NA-K ATPase
how does Na cause secondary active transport (symport with Na+)
Na moving down its electrochemical gradient pulls glucose, amino acids, ions into the cell against their concentration gradient
What are two other reabsorption mechanisms
passive reabsorption, endocytosis
passive reabsorption (e.g. urea)
initially urea=urea
when Na and anions move, H20 drawn via osmotic gradient and urea now has concentration gradieint to move via paracellular transport
endocytosis
megalin binds to small plasma proteins and peptides to be digested by lyosomes in cell
what do the majority of substances transported in the nephron use
membrane proteins
what is saturation of these membrane proteins
max rate of transport that occurs when all available carrier are occupied
what is the transport rate at saturation
transport maximum
what happens when excess glucose is filtered
more glucose then transporter so glucose excreted
renal threshold
plasma concentration of a solute when it first appears in the urine
amount excreted =
Amount filtered - amount absorbed + amount secreted
what is glucose appearing in urine called
glucosuria or glycosuria
what causes the peritubular capillary pressures to favor reabsorpition
colloid osmotic gradient from protein witihin peritubular capillaries draws fluid and dissolved solutes to be reabsorbed
what does the hydrostatic pressure drop to after fluid is removed and resistance encountered
10mmHg
why does the oncotic pressure remain 30mmHg as blood travels to peritubular
plasma proteins are not filtered
what is the net pressure that drives fluid and solutes from interstitial space back into capillaries
20mmHg
30-10
what is secretion
transfer of molecules from ECF into lumen of nephron
what does secretion depend on like reabsorption
membrane transport proteins
what kind of process is secretion
active requiring movement of substances against concentration gradients
purpose of secretion
homeostatic regulation of K+ and H+ (in distal)
organic compound removal (medications, in proximal)
what does secretion enhance
excretion of a substance
when will excretion of a substance be very high
if filtered, not reabsorbed, and then secreted
how are organic solutes secreted
multi step (tertiary) active transport (proximal tubule)
what is tertiary active transport
indirect active ATP process is 3 steps removed from movement of the molecule of interest
oat transporters
organic anion trasnporters
where do OAT transporters use energy from for tertiary indirect active transport
transporting dicarboxylates down their concentration gradient to move organic anions against their concentration gradient
what is a-ketoglutarate
by-product of citric acid cycle
what is direct active transport (tertiary process)
Na-K-ATPase keeps Na in cell low
what is secondary indirect active transport (tertiary process)
Na-dicarboxylate cotransporter concentrates a dicarboxylate in cell using energy from Na gradient
prior to 1930s what was leading cause of death
infection
why was all penicilin ingested be excreted within 3-4 hours
readily filtered and secreted using tertiary process
what would penicillin be given with
probenecid which was preferentially secreted by OAT transporter and prevented penicillin secretion
what does excretion tell us
only what body is eliminating, not renal function
what is GFR an indicator of
overall kidney function
what is renal handling/clearance info necessary for
new drugs
how do we look directly at filtration, reabsorption, and secretion at level of individual nephron
experimentally
indirect methods using analysis of urine and blood
