renal lecture 2 Flashcards
where does reabsorption happen?
through renal epithelial tubular cells
what are the two sides of renal epithelial tubular cells?
apical (lumen/urine) and basolateral (capillary/blood)
what direction does absorption and secretion happen?
absorption - apical -> basolateral
secretion - basolateral -> apical
what are the two types of reabsorbtion?
transcellular (often active - through membranes) and paracellular (passive transport between cells through tight junctions)
how is Na+ transported in the early proximal tubule?
Na+-dependent cotransporters (Na+/glucose) and countertransporters/exchangers (NHE - Na+/H+) that move across apical membrane, and ATPase pumps on basolateral (with facilitated transporters for the other substances)
what is the tonicity of Na+ absorption?
isotonic, so it changes the concentration of other things as water moves with it (because of starling forces)
how is Na+ absorbed in the late proximal tubule?
NHE countertrasnports Na+ and H+ on the aprical membrane, and ATPase countertransports Na+ and K+ on basolateral membrane, NaCl also moves between cells by the transpeithelial Cl- concentration gradient
how is Na+ reabsorbed in the ascending loop of henle?
NKCC (NaKCl cotransporter) moves Na+ in through the apical membrane, ATPase pumps Na+ out and K+ in, and K+ and CL- leave basolaterally (passively)
what is furosemide?
diuretic that targets NKCC to inhibit Na+ reabsorbtion to increase water excretion in the loop of henle
what diuretic targets the ascending loop of henele?
furosemide
how is Na+ reabsorbed in the early distal tubule?
NCC (sodium chloride cotransporter) moves Na+ and Cl- on apical membrane, ATPase contransports Na+ out and K+ in on basolateral (Cl- leaves passively)
what diuretic targets the early distal tubule?
thiazide
what is thiazide?
diuretic that blocks NCC in early distal tubule
how is Na+ reabsorbed in the late distal/collecting duct?
ENaC (epithelial Na+ channel) brings Na+ in on apical, and ATPase brings Na+ out and K+ in through basolateral (K+ leaves through apical)
what diuretic targets the late distal and collecting duct?
K+ sparing diuretic
what is the K+ sparing diuretic?
blocks ENaCs and doesnt promote K+ in urine (like other diuretics) in late distal/collecting duct
why is sodium balance important?
it controls extracellular fluid volume (and blood pressure)
what happens when sodium intake changes?
sodium excretion changes to match (but lags a bit causing sodium retention or sodium loss)
what happens in sodium retention?
osmolarity increases, extracellular fluid increases (to balance), and blood pressure increases
what happens in sodium loss?
osmolarity decreases, extracellular fluid decreases (to balance) and blood pressure decreases
what happens when there is a higher extracellular fluid volume?
sympathetic activity decreases, afferent arteriole dilates, Na+ reabsorption decreases (through increased GFR in duct, decreased PIc in prox, and decreased renin-angiotensin-aldesterone in prox and duct) which all serves to increases excretion
how does angiotensin II increase excretion?
increases Na+ transporter proteins and increases Na+ reabsorption, stimulate aldosterone (which increases activity of ENaCs)
how does ANP affect Na+ reabsorbtion?
released from heart to increase GFR by dilating afferent arteriole and constricting efferent arteriole, decreasing renin/angiotensin II/aldosterone/ADH, and decreases Na+ reabsorption and increases excretion
what is the relationship between angiotensin II and ANP?
opposites - angio increases Na+ reabsorption and ANP decreases Na+ reabsorption
