Renal Physiology

Question 1

Where in the nephron is most of the water absorbed?

Answer 1

Proximal tubule (60-70%)

Question 2

What routes of reabsorption does water take in the proximal tubule

Answer 2

paracellular

transcelluar via AQP1 (basal and basolateral)

Question 3

The main method of Na reabsorption in the proximal convoluted tubule

Answer 3

epithelial sodium transporter (ENaC) and Na/K ATPase

Question 4

What happens in the proximal convoluted tubule

Answer 4

• all nutrients reabsorbed by active transport
• urea and toxins secreted
• water reabsorbed driven by sodium

Question 5

Which transporter is responsible for the majority of glucose reabsorption in the proximal tubule?

Answer 5

low affinity/high capacity SGLT2 and GLUT2

Question 6

Which transporter is responsible for 10% of glucose reabsorption in the proximal tubule?

Answer 6

high affinity/low capacity SGLT1 and GLUT1

Question 7

How are amino acids reabsorbed in the proximal tubule?

Answer 7

via a co-transporter with Na (like and SGLT); different amino acid/different co-transporter

Question 8

Difference between SGLT1 and SGLT2

Answer 8

SGLT1 - 2Na/glucose

SGLT2 - Na/glucose

Question 9

How is bicarbonate reabsorbed in the proximal tubule?

Answer 9

Combines with H+ from the Na/H antiporter

Carbonic anhydrase > H20 + C02 which diffuse into cell

Carbonic anhydrase > C02 + H20 > H2CO3 + H+

HCO3 into interstitium via Na+/3HCO3- symporter

Question 10

Name a weak diuretic which inhibits carbonic anhydrase and the effect this has on blood and urine pH

Answer 10

Acetazolamide

Bicarbonate not reabsorbed so urine becomes more alkaline and metabolic acidosis

Question 11

Describe chloride movement in the early and late proximal tubule

Answer 11

[Cl-] modestly increases along the PT until the gradient drives paracellular transport in the late PT

Question 12

Which transporters are used in Cl transport in the proximal tubule

Answer 12

antiporters with an anion
such as Cl/HCO3 on the basal membrane

Cl/K symporter or Cli channel on basolateral membrane

Question 13

What happens to the small amount of albumin which enters the filtrate?

Answer 13

Very little albumin enters the filtrate, but that which does binds to the plasma membrane of the tubule cells, is endocytosed, then catabolized to its amino acids for subsequent recycling in the body

Question 14

Organic anions compete with each other for secretion in the proximal tubule. They are actively secreted. Which transporters are involved?

Answer 14

organic anion transporters (OATs) on the basolateral membrane: antiporter
multidrug resistant protein (MRP) on the luminal membrane: antiport of organic anion and anion (HCO3, Cl )

Question 15

What is the key function of the thick ascending limb of the loop of henle?

Answer 15

create a hyperosmolar interstitial space in the medulla to drive water loss from the descending limb and cortical collecting duct

Question 16

Which ion transporter is used in the thick ascending loop of henle?

Answer 16

Na+/K+/2Cl- cotransporter NKCC2

Question 17

What happens to K+ in the thick ascending loop of henle?

Answer 17

It is recycled back into the filtrate to maintain reabsorption of NaCl

Question 18

What is reabsorbed in the descending loop of henle?

Answer 18

Water ONLY via AQP

Question 19

What is reabsorbed in the ascending loop of henle?

Answer 19

Na, Cl

Mg, Ca absorbed passively

Question 20

How is Na absorbed in the distal tubule

Answer 20

symport with Cl

then 3Na/2K antiport and Cl/K symport

Question 21

Water reabsortion in the collecting tube is via which channels?

Answer 21

AQP2 in luminal membrane

AQP3 in the basolateral membrane

Question 22

Na reabsortion in the collecting tube is via which channels?

Answer 22

ENaC in luminal membrane
Na/K ATPase in the basolateral membrane
synthesis stimulated by aldosterone

Question 23

K secretion in the collecting tube is via which channels?

Answer 23

K channel in luminal membrane (ROMK) - under control of aldosterone
Na/K ATPase in the basolateral membrane

Question 24

What happens in the distal convoluted tubule

Answer 24

Active transport of Na and Cl under control of aldosterone

Ca reabsorption under control of PTH

Question 25

Which hormone triggers ADH release from the post. pituitary?

Answer 25

angiotensin II

Question 26

Which part of the nephron is impermeable to water

Answer 26

TAL

Question 27

Which parts of the nephron are impermeable to urea

Answer 27

DT and cortical collecting duct