Nephron Physiology B&B

Question 1

Hartnup disease

Answer 1

no tryptophan transporter in proximal tubule of kidney —> tryptophan deficiency —> amino acids in urine and skin rash (plaques, desquamation)

Under normal conditions, should not find amino acids in urine

Question 2

Explain how carbonic anhydrase inhibitors can be used as weak diuretics

Answer 2

carbonic anhydrase is required for dissociating H2CO3 into H+ and HCO- within renal tubular epithelium cells… this allows H+ to be secreted into the lumen, where it combines with HCO3- to form H2CO3… carbonic anhydrase in the lumen dissociates H2CO3 into CO2 and H2O, and H2O diffuses into epithelium (it’s a cycle)

carbonic anhydrase results in bicarb loss in the urine

Question 3

what is the effect of a type II renal tubular acidosis on bicarb levels?

Answer 3

ion defect causes an inability to absorb bicarb —> metabolic acidosis

Question 4

Fanconi Syndrome

Answer 4

non-functional proximal tubule —> impaired reabsorption of solutes —> polyuria, polydipsia (diuresis from glucose) despite normal serum glucose (differentiate from diabetes)

—> non-anion gap acidosis due to loss of HCO3-, hypokalemia (high nephron flow), hypophosphatemia, amino acids in urine

Question 5

What is the inherited form of Fanconi syndrome associated with?

Answer 5

Cystinosis: lysosomal storage disease that causes accumulation of cystine - presents in infancy with Fanconi syndrome

Fanconi syndrome: loss of proximal tubule functions

Question 6

What causes cystinuria?

Answer 6

proximal tubule defect that causes impaired reabsorption of cystine —> cystine kidney stones

Question 7

which of the following is not a known acquired cause of Fanconi syndrome?
a. lead poisoning
b. silicosis
c. multiple myeloma
d. Cisplatin (chemotherapy)
e. Tenofovir (HIV drug)

Answer 7

Fanconi Syndrome: loss of proximal tubule function, acquired causes include:

a. lead poisoning
c. multiple myeloma
d. Cisplatin (chemotherapy)
e. Tenofovir (HIV drug)

(as well as many other drugs)

Question 8

which of these will show a decrease in the ratio of [tubule]/[plasma] as it travels along the proximal tubule?
a. PAH
b. inulin
c. creatinine
d. Na+
e. K+
f. HCO3-
g. glucose
h. urea

Answer 8

glucose, amino acids, and HCO3- will be reabsorbed more than they are secreted —> low [tubule]/[plasma] ratio (because more will be reabsorbed into the plasma than remain in the tubule)

Question 9

how does osmolarity of the nephron change as it descends from the cortex to the outer medulla to the inner medulla?

Answer 9

Cortex = 300 MOSM
Outer medulla = 600 MOSM
Inner medulla = 1200 MOSM

In this way, urine becomes concentrated as a descends into the medulla (water drawn out by hypertonicity in medulla)

Question 10

Match the following:
thin descending loop of Henle vs thick ascending loop of Henle
with
Permeable to water vs permeable to sodium

Answer 10

thin descending = permeable to water (not NaCl)

thick ascending = permeable to NaCl (not water - just think of water being trapped in thick ascending and making it look bloated, or thick)

Question 11

what are the three overall effects of aldosterone on the kidneys?

Answer 11

1. Sodium/water reabsorption (increase effective circulating volume)
2. Potassium excretion
3. H+ excretion