PCT and LoH Transport

Question 1

what are two modes of transport in epithelium of nephron?

Answer 1

transcellular and paracellular

Question 2

what creates the luminal sodium gradient for reabsorption in the pCT?

Answer 2

basolateral Na/K ATPase pump keeps Na really low in epithelial cell

Question 3

what is it considered when sodium moves into the luminal membrane following the gradient created by the pump in the basolateral membrane?

Answer 3

secondary active transport

Question 4

name the four molecules that are co transported with Na through the luminal surface of the PCT

Answer 4

Cl
Glucose
Amino Acids
phosphate

Question 5

what is an antiport that Na has on the luminal surface of the PCT?

Answer 5

H+ goes into lumen and Na goes into epithelial cells

Question 6

name the luminal glucose sodium co transporter in the PCT

Answer 6

sodium dependent glucose transporter

Question 7

name the basolateral membran glucose transporter in the PCT

Answer 7

glucose transporter

Question 8

what is the baso lateral cotransporter that is present in the PCT

Answer 8

bicarb and sodium

Question 9

how does water pass in luminal and out basolateral surface of PCT?

Answer 9

aquaporin 1

Question 10

why does diabetes lead to glucose in urine?

Answer 10

glucose is freely filtered and the sodium dependent glucose transporters have a max number and glucose will remain in the urine and hold onto water

Question 11

what are the two ways to reabsorb bicarbonate into the luminal part of the PCT?

Answer 11

either reclaim that of which has been secreted or use glutamine to make new bicarbonate

Question 12

describe what happens to bicarb in the lumen of the PCT?

Answer 12

it is turned into CO2 and H2O because of the acidic environment and presence of carbonic anhydrase in the brush border enzymes

Question 13

once bicarb is CO2 and H2O in the lumen of PCT, what can happen?

Answer 13

it can diffuse into the luminal surface of the epithelium

Question 14

once CO2 and H2O are in the epithelium what occurs?

Answer 14

bicarb is remade by carbonic anhydrase and cotransported out of the basolateral membrane with sodium

Question 15

what is glutamine turned into in the epithelial cell of the PCT?

Answer 15

NH4 and bicarb

Question 16

what happens to the NH4 that is made in epithelial cells of the PCT?

Answer 16

it is secreted into lumen via Na/H+ antiporter on luminal surface of the PCT

Question 17

what is the main mechanism of K+ reabsorption in the PCT?

Answer 17

solvent drag as it rides along with H2O in the paracellular transport

Question 18

explain how urea re-absorption occurs in the PCT?

Answer 18

it passively follows its concentration gradient, but requires the movement of some water out of the PCT to make a greater concentration gradient for it to follow

Question 19

what happens to urea when you decrease the GFR? why is this?

Answer 19

you get increased plasma levels because the filtrate spends more time in the PCTs where urea can be reabsorbed and you get high plasma urea and BUN levels

Question 20

name three common things secreted in the PCT

Answer 20

end products of metabolism
pollutants
drugs

Question 21

what is the mechanism of secretion in the PCT? why can this be a problem?

Answer 21

non specific transporters…so things can compete for the transporters and may get increasing conc if transporters are taken

Question 22

what is the name of the transporter on the luminal side of the ascending loop of henle?

Answer 22

NKCC transporter

Question 23

what molecules does the NKCC transporter transport into the medulla

Answer 23

sodium, potassium and two chlorides

Question 24

on the luminal surface of the ascending loop of henle there is an important transporter that sends K+ into the lumen, what is its name?

Answer 24

ROMK channel

Question 25

what is required to drive the NKCC channel?

Answer 25

tubular K+

Question 26

what maintains the Na+ gradient in the luminal surface of the ascending loop?

Answer 26

Na/KATPase

Question 27

what is the horizontal gradient in the loop of henle?

Answer 27

200 mOsm higher in the descending compared to ascending

Question 28

what molecule increases the medullary gradient in the loop of henle that is associated with ADH?

Answer 28

urea

Question 29

other than water reabsorption, what does ADH pull into interstitial area?

Answer 29

urea

Question 30

when urea gets into interstitum after being reabsorbed through ADH, what happens to it?

Answer 30

it goes back into loop of henle so it is trapped in a cycle between collecting ducts and loop of henle and interstitum

Question 31

what three things contribute to the magnitude of the longitudinal osmotic gradient in the loop of henle

Answer 31

urea
length of loop of henle
rate of flow in loop

Question 32

does increased flow rate in the loop lead to lower or higher osmolality gradient in the loop?

Answer 32

lower gradient