SS3. Secundary active transport in the nephron

Question 1

How does reabsorption in the proximal convoluted tubule work?

Answer 1

Glomerular filtrate in lumen with apical sid of cells facing lumen, basolateral membrane facing the peritubular capillary.

1) Na/K on basolateral side: Na+ in pump, ATP causes conform. change, sends Na+ in blood. K+ moves from blood into cells (3Na, 2K) aka active transport.
2) BC Na+ active pumped out, low Na+ in cells –> Na+ from filtrate moves into lumen via symporter & glucose comes along.

Question 2

How does reabsorption in the ascending limb of the Loop of Henle work?

Answer 2

Works the same as reabsorption in proximal convoluted tubule

1) Na+ pumped to blood, K+ pumped out of blood into cell, now low Na+ in cell. Na+ from lumen wants to enter cell
2) Cl and K+ and Na+ enter via NKCC2, the Sodium potassium chlorine cotransporter 2.

Question 3

What type of transport is the reabsorption in the ascending loop of Henle?

Answer 3

Secondary transport. Cl makes its way out, making hte medulla saltier.

Question 4

How does reabsorption in the distal convoluted tubule work?

Answer 4

1) Na+ moves out the cells into the blood, K+ moves from blood into cell, now low Na+ in the cell.
2) Cell is porous for Ca. With antiporter, Na+ goes in, Ca+ moves into blood cell.
Also secondary transport.