Nephron physiology

Question 1

Early proximal tubule

Answer 1

Contains brush border
Reabsorbs all the glucose and AA
most bicarb, Cl, phosphate and water

Isotonic absorption

Generates and secretes ammonia, which acts as a buffer for secreted H+

65-80% Na+ reabsorbed

Question 2

Early proximal tubule: PTH

Answer 2

inhibit Na+/phosphate cotransport

thus phosphate excretion

Question 3

Early proximal tubule: AT II

Answer 3

stimulates Na+/H+ antiport

Increases Na+, H2O, and bicarb reabsorption.
permits contraction alkalosis

Question 4

Thin descending loop of Henle

Answer 4

Passively reabsorbs water via medullary hypertonicity

Question 5

Thick ascending loop of Henle

Answer 5

Actively absorbs Na+, K+, and Cl-

Indirectly induces the paracellular reabsorption of Mg and Ca through (+) lumen potentially generated by K+ backleak.

Impermeable to H2O.

10-20% of Na+ reabsorbed.

Question 6

Early distal convoluted tubule

Answer 6

Actively reabsorbs Na+ and Cl-
Makes urine hypotonic

5-10% Na+ reabsorbed

Question 7

Early distal convoluted tubule: PTH

Answer 7

PTH: increases Ca2+/Na+ exchange

thus increases Ca2+ reabsorption

Question 8

Collecting tubule

Answer 8

Reabsorbs Na+ in exchange for secreting K+ and H+ (regulated by aldo)

3-5% Na+ reabsorbed

Question 9

Collecting tubule: aldo

Answer 9

acts on mineralocorticoid receptor

Insertion of Na+ channel on luminal side

Question 10

Collecting tubule: ADH

Answer 10

acts at V2 receptor

insertion of aquaporin H2O channels on luminal side