5 - reabsorption & secretion Flashcards
what is the result of 20% plasma being in the bowman’s capsule for filtration?
blood in the efferent arteriole and peritubular capillaries has higher plasma proteins conc and increased oncotic pressure
what is the balance of starlings forces in these vessels and what does this mean?
decreased PC pressure and increased oncotic P
leads to reabsorption being favoured in PCs
where is H2O, GLC etc. filtered and where is it then reabsorbed?
filtered in the glomerulus, reabsorbed in the proximal convoluting tubule
name 3 substances that are reabsorbed by carrier mediated transport systems?
GLC
amino acids
phosphate
why do carriers have a Tm?
saturation of carriers
what is Tm?
maximum transport capacity
result of Tm being exceeded?
excess substrate enters urine
function of carrier molecules?
allow larger molecules (e.g. GLC) to cross the membrane for reabsorption
how is Tm decided?
by the number of carriers
what is the renal threshold?
plasma threshold @ which saturation occurs
relationship between GLC plasma conc and how much is filtered?
whatever the GLC plasma conc, that amount will be filtered out
what is the renal threshold for GLC?
10mmol/L
Tm for GLC?
10mmol/L
once it has all been filtered, what happens to GLC?
vast majority will be absorbed, if it exceeds 10mmol/L - some will be excreted
normal plamsa GLC?
5 mmol/L
how is GLC regulated?
insulin and counter regulatory hormones
what is the benefit of Tm for GLC being set at 10 when the normals plasma GLC is only 5?
ensures that GLC is all reabsorbed as it is a precious energy source
what is glycosuria?
GLC in urine
what is glycosuria a result of?
failed insulin control, not failed kidneys
why are sulphate and phosphate ions not regulated by Tm?
Tm is set at a level whereby normal blood plasma conc causes saturation of carriers
what is the result of any increase in phosphate or sulphate molecules?
excretion
effect of PTH on reabsorption of GLC?
decreased reabsorption
describe 3 renal processes?
1 - substances reabsorbed by ,mediated transport systems
2 - reabsorption of Na+ ions
3 - tubular secretion
where is Na+ most abundant?
ECF
where is ~75% of Na+ reabsorption?
proximal tubule
how is Na+ regulated?
by active transport, creating a gradient for Na+ to cross the tubule wall
what drives the reabsorption of Na+?
Na+ pumps
location of the Na+pumps?
on basolateral surfaces - i.e. high density of mitochondria
how does Na+ move into cells?
passively
why do Na+ ions move into cells passively?
due to brush border of proximal tubule cells having increased permeability to Na+ ions than other membranes
why do proximal tubule cells have increased permeability to Na+ions?
due to microvilli (increased surface area) and increased number of Na+ ion channels
