Kidney Function

Question 1

What molecules affect osmolarity?

Answer 1

Molécules that can dissociate eg ethanol, glucose, salt
Not urea or creatinine

Question 2

Ms L, 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]

Answer 2

Respiratory compensation-hyperventilation
When you are hyperventilation you are breathing faster so the amount of CO2 reduces and the amount of oxygen reduces too
When you have a lower HCO3- it means you are reapsorbing less carbonate = more acidic pH

Question 3

Why do most diuretics increase potassium secretion?

Answer 3

They increase in flow rate is detected in the collecting duct and directly stimulates potassium excretion

Question 4

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?

Answer 4

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.

Question 5

If a patient is dehydrated (although it doesn’t matter), the filtrate present in which of these areas highest osmolarity?
1. Bowman’s capsule
2. Tip of loop of Henle
3. Before distal convoluted tubule
4. Start of medullary collecting duct

Answer 5

Tip of loop of Henle where the fluid is isosmotic

Question 6

The urine samples of different patients were analysed using the urine osmolarity test. Whose sample is likely to have the highest osmolarity?
1. Patient with loss of function V2 receptor mutation
2. Patient suffering with central diabetes insipidus
3. Patient with loss of function of UT-B1 urea transporter
4. Patient with hepatic cirrhosis
Explain urea recycling
What is the role of UT-B1

Answer 6

4
UT-B1 transporter puts urea into the descending vasa recta
When it reaches the ascending vasa recta it leaves back into the interstitium due to the concentration gradient to maintain a high interstitial urea concentration and cause water to come out of descending loop of henle (urea recycling)
UT-B1 keeps urea in interstitial space so it doesn’t go into the cortex (area of lower concentration)