The renal system lecture 3 Flashcards
what is the proximal tubule concerned with ?
the uptake and secretion of several solutes and water, but the fluid in the tubule remains isotonic throughout.
what does the apical surface of the cells have in the proximal tubule ?
numerous microvilli which enhance their transport
what are the functions of the proximal tubule ?
reabsorption of the bulk of filtered NaCl as isotonic NaCl solution , essential solutes, e.g. glucose and all amino acids
regulation of body fluid pH (by bicarbonate reabsorption)
secretion of some organic molecules
what is the reabsorption ?
the net movement from apical to base-lateral membrane
what is secretion ?
the net movement from the base-lateral to apical membrane
what are the two types of reabsorption/secretion ?
transcellular/paracelluar
About X? of the filtered load of NaCl is reabsorbed, but tubular fluid remains isotonic
80% of the filtered load of NaCl is reabsorbed, but tubular fluid remains isotonic
how is the Na+ transported into the epithelial cells of the proximal tubule ?
secondary active transport - coupled counter-transport with other molecules
how is the Na+ removed from the base-lateral surface of the proximal tubule ?
by primary active transport - the Na pump. Cl- and H20 follow passively therefor isotonic NaCl reabsorption has occurred
what is the co-transport of Na+ into the apical side of the epithelium cells of the proximal tubule linked with ?
with glucose transporters SGLT2.
how does glucose leave the base-lateral surface of the proximal tubule ?
by facilitated diffusion via GLUT2 - the number of transporters is sufficient to ensure that all solutes are generally reabsorbed
what is the co-transport of Na+ into the apical side of the epithelium cells of the proximal tubule linked with ?
with amino-acid transporters. these then the base-lateral membrane by diffusion
describe 4 properties of glucose clearance ?
freely filtered
reabsorbed by the tubule from lumen to blood
not metabolised
does not affect GFR itself
why is the proximal tubule useful ?
it reabsorbs useful substrates from the filtrate that otherwise would be lost in the urine
what type of process is glucose reabsorption ?
A carrier-mediated process - and there has a maximum transport rate - the tubular transport maximum or Tmax
