Kidney Function TBL

Question 1

1. If a patient is dehydrated, the filtrate present in which of these areas will have the highest osmolarity?

A - Bowman’s capsule
B - Tip of Loop of Henle
C - Before Distal Convoluted Tubule
D - Start of medullary collecting duct

Answer 1

B -Tip of Loop of Henle - lose all water passively due to high osmolarity of interstitial fluid (1200)

Question 2

2. The urine samples of different patients were analysed using the urine osmolarity test. Whose sample is likely to have the highest osmolarity?

A - Patient with loss-of-function V2 receptor mutation
B - Patient suffering from central diabetes insipidus
C - Patient with loss-of-function UT-B1 urea transporter mutation
D - Patient suffering from hepatic cirrhosis

Answer 2

D - Patient suffering from hepatic cirrhosis = lots of ADH being released = concentrated urine

A and B eliminated as water is not being reabsorbed (due to lack of ADH effect)

C - can no longer trap urea in the interstitial fluid to increase medullary interstitial osmolarity
The urea can freely diffuse out wherever it wants - so the concentration required in the interstitium is not achieved = less water diffuses out of Loop of Henle = more dilute urine

Question 3

3. An athlete after finishing their London Marathon run drank 2L of distilled water. Which of the following statement is correct about their body fluids?

A - Decrease in Extracellular Fluid (ECF) volume.
B - Decrease in plasma osmolarity
C - Decrease in Intracellular Fluid osmolarity
D - Decrease in interstitial fluid volume

Answer 3

B - more correct answer

C - correct, but ICF requires some time to equilibrate

A and D = eliminated as volume does not change straight away

Question 4

4. The increase in plasma concentration of which solute will have no effect on ADH production?

A - Glucose
B - Urea
C - Salt
D - Ethanol

Answer 4

B - urea = solute equilibrates itself so no net water movement = nothing is detected by osmoreceptors

A and C - increase in salt and glucose invites water from ICF to flow into plasma = detected by osmoreceptors = increased ADH production and release

D - ethanol directly acts on hypothalamus, alcohol = diuretic

Question 5

5. Sodium excretion is very limited (less than 1% of filtered load) and several mechanisms exist to tightly regulate it. Increasing sodium excretion reduces water retention. Potassium excretion can vary over a very large range (from 1 to 80% of filtered load). Why doesn’t this variability in potassium excretion have a marked effect on water balance?

A - Potassium is only excreted in the distal nephron so there is no time for it to have an effect on osmolarity.
B - Potassium is a major intracellular ion, so the variability affects intra-cellular fluid volume not extracellular fluid volume.
C - The amount of potassium in the plasma and extracellular is much lower than the amount sodium so that variations in this amount are insufficient to have a marked effect on water balance.
D - Whilst the amount of potassium in the tubular fluid in the collecting duct varies its concentration does not so it does not affect osmolarity.

Answer 5

C - The amount of potassium in the plasma and extracellular is much lower than the amount of sodium so that variations in this amount are insufficient to have a marked effect on water balance

B - true, but only small amount of potassium excreted
A - true, but not major contributor as it is not major solute in ECF
D - does affect osmolarity, just a small amount though = not a big effect

Question 6

6. Why do most diuretics increase potassium excretion?

A - They reduce the uptake of K+ by the Na/K/Cl transporter.
B - The increase in sodium in the distal nephron is exchanged for potassium in the collecting duct because of the change in membrane potential.
C - The increase in flow rate is detected in the collecting duct and directly stimulates potassium excretion.
D - They cause a rise in plasma pH and this stimulates potassium export.

Answer 6

C - the increase in flow rate is detected in the CD and directly stimulates potassium excretion

A - true, but only loop diuretics
B - false, there is import of sodium and export of potassium
D - does not really affect plasma pH

Question 7

7. Mr Holmes (65 years old, 75 Kg) is being treated with a loop diuretic and Mr Smith (66 years old, 74 Kg) with a thiazide diuretic for past 3 weeks (assume that the doses of the respective treatments allow an equivalent inhibition of [Na+] reabsorption). Both the individuals are drinking insufficient but equivalent amount of water. Which of the following statement is likely to be true?

A - Mr Holmes urine will have higher osmolarity than Mr Smiths.
B - Mr Holmes urine will have lower osmolarity than Mr Smiths.
C - Both Mr Holmes and Mr Smith’s urine will have similar osmolarity.
D - Information provided is insufficient to reach any logical conclusion.

Answer 7

B - Mr Holmes urine will have lower osmolarity than Mr Smiths

For thiazide normally sodium reabsorbed goes into cortical space instead

Loop diuretic has a greater effect than thiazide - so Mr Holmes has a lower osmolarity than Mr Smith in their urines

Question 8

8. Ms Sethi, a 25-year-old woman while trekking the Himalayas develops symptoms of dizziness and pain. Following data was collected for her: Blood pH = 7.6, [HCO3-] = 16mEq/L, PCO2 = 25mmHg. Identify her acid-base disorder.
   [Normal values: Blood pH = 7.4, [HCO3-] = 24mEq/L, PCO2 = 40mmHg]

A - Metabolic alkalosis
B - Respiratory alkalosis
C - Metabolic acidosis
D - Respiratory acidosis

Answer 8

B - Respiratory alkalosis

Low bicarb (metabolic renal compensation), low pCO2, high pH

Hyperventilation at high altitudes = common

Question 9

9. Ms Li, a 25-year-old healthy woman on her holiday develops stomach infection with nausea and vomiting. Following data was collected for her: Blood pH = 7.1, [HCO3-] = 16mEq/L, PCO2 = 30mmHg. Identify the compensatory mechanism being used by her body. [Normal values: Blood pH=7.4, [HCO3-] = 24mEq/L, PCO2 = 40mmHg]

A - Renal compensation – Reduced reabsorption of Bicarbonate ions
B - Renal compensation – Reduced excretion of ammonia and proton ions
C - Respiratory compensation – Hypoventilation
D - Respiratory compensation – Hyperventilation

Answer 9

D - Respiratory compensation - Hyperventilation

Metabolic acidosis

Low pH, low bicarb, low(ish) pCO2

Question 10

10. Ms Juan, a 25-year-old woman with a history of asthma, on her holiday develops stomach infection with diarrhoea. Following data was collected for her: Blood pH = 7.1, [HCO3-] = 16mEq/L, PCO2 = 45mmHg. Identify her acid-base disorder.
    [Normal values: Blood pH = 7.4, [HCO3-] = 24mEq/L, PCO2 = 40mmHg]

A - Metabolic acidosis
B - Respiratory acidosis
C - Mixed alkalosis
D - Mixed acidosis

Answer 10

D - Mixed acidosis

Both - has asthma (lack of proper gas exchange) and diarrhoea (loss of bicarb)

To compensate for this, begin by treating diarrhoea to normalise bicarb first

Low pH, low bicarb, high pCO2