transport across nephron

Question 1

Which of the following is true about the loop of henle?

a. Thick descending limb forms hypotonic urine
b. Thin ascending limb is where frusemide acts
c. Frusemide blocks the Na-Cl cotransporter to cause diuresis
d. Resulting solution is hypotonic

Answer 1

d. Resulting solution is hypotonic

a. THIN descending limb produce hypertonic urine
b. frusemide acts on thick ascending limb
c. NKCC transporter

Question 2

Which of the following is true of the proximal convoluted tubule?

a. SGLT2 inhibitors work here to inhibit the sodium-phosphate cotransporter
b. Hydrochlorothiazide works here to inhibit the sodium chloride cotransporter
c. Acetazolamide works here by upregulating carbonic anhydrase and causing alkaline
diuresis
d. Reabsorption here is isotonic

Answer 2

d. Reabsorption here is isotonic

a. sodium glucose linked transporter
b. thiazides act on early DCT
c. downregulates

Question 3

Which of the following is true about the early DCT?

a. Parathyroid hormone causes upregulation of Ca reabsorption here
b. Urine becomes slightly hypertonic here as water is reabsorbed
c. Thiazides can work here to inhibit NKCC cotransporter to causes diuresis
d. A prominent brush border can be seen on histology

Answer 3

a. Parathyroid hormone causes upregulation of Ca reabsorption here

b. urine here is hypotonic
c. Na-Cl cotransporter

Question 4

Are these true/false about the late DCT?

a. Amiloride upregulates the H/K pump of intercalated cells to maintain acid-base
homeostasis of the body
b. V2 aquaporins, signalled by ADH, are inserted on the luminal side of intercalated cells to increase water reabsorption
c. Alpha intercalated cells are involved when the body is alkalotic and needs to reabsorb
acids and secrete bases
d. Beta intercalated cells are involved when the body is alkalotic and needs to reabsorb
acids and secrete bases

Answer 4

d. Beta intercalated cells are involved when the body is alkalotic and needs to reabsorb acids and secrete bases

a. inhibits Na+ channels on principal cells to cause diuresis
b. principal cells

Question 5

where is filtered Na+ reabsorbed?

Answer 5

proximal tubule, ascending limb of LoH, distal tubule, collecting ducts

Question 6

where is filtered water reabsorbed?

Answer 6

proximal tubule, descending limb of LoH, distal tubules, collecting ducts

Question 7

what is renal threshold?

Answer 7

plasma concentration at which a substance (eg. glucose) is first excreted in the urine –> when one nephron becomes saturated

Question 8

what is transport maximum (Tm)?

Answer 8

rate at which all transporters are saturated (ie. highest reabsorption rate)

Question 9

what is the relation of filtration/reabsorption/excretion of glucose with respect to its plasma concentration?

Answer 9

1. filtration is proportional to plasma concentration
2. reabsorption is proportional to plasma concentration until transport maximum is reached
3. excretion is zero until renal threshold is reached

Question 10

how does aldosterone control Na+ reabsorption?

Answer 10

proximal convoluted tubule

Question 11

what factors increase HCO3- reabsorption?

Answer 11

1. increased luminal [HCO3-]
2. slower luminal flow rate
3. increased arterial pCO2
4. increased angiotensin II
   - increase Na+ reabsorption –> creates electrochemical gradient favourable for HCO3- reabsorption via Na+/HCO3- co-transporter
   - increased carbonic anhydrase activity –> increased formation of H+ and HCO3- that is transported into lumen –> more HCO3- generated and transported back into cells

Question 12

where is NH4+ produced predominantly?

Answer 12

proximal convoluted tubular cells

Question 13

how is NH4+ produced from glutamine?

Answer 13

metabolism of glutamine to a-ketoglutarate by action of glutaminase (glutamine + H2O –> glutamate + NH4+)

Question 14

what are two conditions that promote NH4+ synthesis?

Answer 14

1. systemic acidosis
   - high [H+] in body –> high [HCO3-] used up for neutralisation –> increased NH4+ synthesis to regenerate HCO3-
2. systemic hypokalaemia
   - decreased [K+] in blood –> Na+/K+ ATPase pump not working as well –> Na+/HCO3- symporter work more to pump Na+ into plasma –> Na+/H+ antiporter work more to pump Na+ from lumen into tubular epithelial cell –> more H+ into lumen –> more HCO3- needed –> increased NH4+ synthesis

Question 15

what are the types of cells in collecting tubules?

Answer 15

1. prinicpal cells
2. intercalated cells
   - alpha-intercalated (contains H+/K+ ATPase pump and H+ pump on apical surface)
   - beta-intercalated (contains Cl-/HCO3- co-transporter on apical surface)

Question 16

what happens to intercalated cells during metabolic acidosis?

Answer 16

beta-intercalated cells become alpha-intercalated cells to secrete more H+ and return pH back to normal

Question 17

the reabsorption of bicarbonate ions by the PCT is associated with:
a) excretion of K+ ions
b) excretion of H+ ions
c) reabsorption of Ca2+ ions
d) reabsorption of phosphate ions

Answer 17

b) excretion of H+ ions