Question

We know a lot about the nephron from the study of isolated segments and by analyzing fluid that enters the segment and how it is altered as it progresses through.

Researchers collected samples of fluid entering and leaving a particular nephron segment that was immersed in a bath solution and then compared the volume and chemical composition of the two fluids to determine if any reabsorption or secretion had occurred.  

The fluid volume entering the segment was 1.0 ml and the volume leaving was 0.25 ml (over a given time period). The [Na+] was equal in both fluids, while the [Ca++] was 4 times greater and the [K+] was 5 times greater in fluid leaving the segment. Describe how this segment of the nephron segment handled H2O, Na+, Ca++and K+. Explain your answers.

Hint: concentration = amount/volume

Answer 1

This segment of nephron had ;

1) 75% Reabsorption of Sodium and along with sodium 75% reabsorption of water.

As both sodium and water are Reabsorbed in equal proportions, Sodium concentration remain equal on both the ends of nephron, while volume reduced to 0.25 ml.

2) K+ neither Reabsorbed nor secreted :

As volume of fluid reduced by 1/4 th , concentration of K+ is apparently Increased 4 times.

3) 25% Ca++ tubular secretion : As Ca++ concentration is 5 times of intial. As volume is reduced by 1/4th, appareno Increase by 4 times is due to volume reduction. Remaining increase of 1 time i.e. 25% is by tubular secretion.