Sun28November0440PM 21

A sample of fluid is taken from a section of nephron using a micropipette.

Biochemical analysis of the fluid is as follows:

Na+ 142 mmol/L

K+ 4.5 mmol/L

Cl- 110 mmol/L

Glucose 5.5 mmol/L

Bicarbonate 27 mmol/L

Which one of the following segments of a nephron is this fluid most likely to have sampled?

(Please select 1 option)

Thick ascending loop of Henle Incorrect answer selected

Distal convoluted tubule

Bowman's capsule This is the correct answer

Proximal convoluted tubule (S3) or pars recta

Collecting ducts

Explanation

Substances with a small molecular weight (MW) below 30,000 Da are freely filtered by the glomerulus. The glomerular filtrate will contain the same concentrations of electrolytes, glucose and aminoacids.

Proteins such as albumin (MW 70,000 Da) are filtered in very small quantities.

The other important factor influencing passage of substances is electrical charge. The basement membrane and podocytes are negatively charged and repel similarly charged molecules. Negatively charged molecules are therefore less able to pass across. The loop of Henle, distal convoluted tubule and the collecting ducts will not contain glucose because reabsorption would have occurred in the proximal convoluted tubule.

The electrolyte composition of other parts of the nephron would not match that of plasma because of varying degrees of water and electrolyte reabsorption.

Answer Statistics

1

2%

2

9%

3

68%

4

15%

5

8%

Times answered: 234