9.9 - Renal TBL Flashcards
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 DCT
D. Start of medullary collecting duct
B - Tip of LoH
Not D as at the START of the collecting duct, the filtrate is dilute (but becomes more and more concentrated down)
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
D - Patient suffering from hepatic cirrhosis - this is an example of SIADH. The body retains water so we want the hypothalamus to reduce ADH production and close AQP channels. But the patient has increased vasodilation, which reduces BP (reduced albumin = reduced H2O in blood = reduced BP). Reduced BP is detected by baroreceptors which signals to hypothalamus to increase ADH secretion and H2O retention –> concentrated urine
(Not C since Ut-B1 urea transporter allows urea to enter the vasa recta system and circulate the medullary region. A mutation in this would mean it diffuses out of the system, so high osmolarity in the region is not maintained and less water is reabsorbed –> dilute urine)
An athlete after finishing their London Marathon run drank 2L of distilled water. Which of the following statements is correct about their body fluids?
A. Decrease in ECF volume
B. Decrease in plasma osmolarity
C. Decrease in ICF osmolarity
D. Decrease in interstitial fluid volume
B. Decrease in plasma osmolarity
C is also correct but water moves into the ECF first, and then into the ICF later (so B is more correct)
The increase in plasma concentration of which solute will have no effect on ADH production?
A. Glucose
B. Urea
C. Salt
D. Ethanol
B - Urea
Glucose and salt cause H2O movement
Urea - ineffective osmole, movement of urea does not lead to movement of H2O, no osmoreceptors stimulated
Ethanol - diuretic, decreases ADH production
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. K+ is only excreted in the distal nephron so there is no time for it to have an effect on osmolarity
B. K+ is a major intracellular ion, so the variability affects intra-cellular fluid volume not extracellular fluid volume
C. The amount of K+ in the plasma and extracellular fluid is much lower than the amount of sodium, so variations in this amount are insufficient to have a marked effect on water balance
D. Whilst the amount of K+ in the tubular fluid in the collecting duct varies, its concentration does not so it does not affect osmolarity
C. The amount of K+ in the plasma and extracellular fluid is much lower than the amount of sodium, so variations in this amount are insufficient to have a marked effect on water balance
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
C - The increase in FLOW RATE is detected in the collecting duct and directly stimulates potassium excretion
A - only loop diuretics e.g. furosemide
B - true but only a minor effect
Mr Holmes (65y/o, 75kg) is being treated with a loop diuretic and Mr Smith (66y/o, 74kg) 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 statements 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
B - Mr Holmes urine will have lower osmolarity than Mr Smiths (less water reabsorbed due to lower gradient - essentially loop diuretic is more effective than thiazide diuretic)
Ms J, a 25-year-old woman with a history of asthma, on her holiday develops stomach infection with diarrhoea. Following data was collected (normal values in brackets): blood pH=7.1 (7.4), [HCO3-]=16mEq/L (24mEq/L), PCO2=45mmHg (40mmHg). Identify her acid base disorder.
A. Metabolic acidosis
B. Respiratory acidosis
C. Mixed alkalosis
D. Mixed acidosis
D - Mixed acidosis
