Tubular Transport

Question 1

Proximal tubular transport

Answer 1

Huge surface area
reabsorb most filtered water, Na, K, Cl, Bicarb, Ca, Phos

Reabs ALL glucose and AA

secretes organic anions and cations (drugs, creatinine, urate)

Question 2

what drives proximal tubular Na reabsorption

Answer 2

polarity of epithelial cell membranes
IC Na is very low due to basolateral membranes
Na wants to move down its CG (USUALLY COUPLED-think GLUT)

Question 3

Bulk flow

Answer 3

Na reabsorption PCT increases OSM of interstitium, this draws water out of tubular fluid

Question 4

Glucosuria

Answer 4

occurs after Na/Glucose cotransporters have become saturated —>glu enters urine

same principles apply to AA transport (in IEM disorders)

Question 5

Tubular glucose maximum

Answer 5

TMg= max rate of glucose reabs by all the nephrons combined

flattens out once all the nephrons have saturated their cotransporter

Question 6

Polydypsia

Answer 6

exs thirst stimulated by increased plama Osm

Question 7

Polyurea

Answer 7

increased Osm in the filtrate which draws more water back into the tubules

also increased by polydypsia

Question 8

secretion of organic anions

Answer 8

tertiary active transport

1) NaK ATPase
2) K entry into the cell is coupled with a cotransporter which brings in organic anions into the cell, then on the apical side, they are moved into the urine

**saturable process

Question 9

TF/P ratio of PAH at PCT

Answer 9

=10
not only is water lost, but PAH is secreted

excreted>filtered

Question 10

PAH of inulin at PCT

Answer 10

=3
Water is reabsorbed (inversely) proportionally
in this case 2/3 of filtered water is reabsorbed

Question 11

PAH of glucose at PCT

Answer 11

=0
all glucose is reabsorbed

AA, and HCO3- are slightly less but similar

Question 12

biochemistry of acids and bases

Answer 12

weak acids are neutral when protonated
weak bases are neutral when deprotonated

Neutral compounds are membrane-permeable