Control of volume

Question 1

How does water move in and out of cells?

Answer 1

due to osmotic treated created by the movement of Na+ and its concentration in the ECF
-if Na+ in the ECF changes, volume of ECF changes which will affect circulating volume (and hence BP)

Question 2

What is the sodium ion balance?

Answer 2

the kidneys must balance the amount of sodium ion excretion so that it matches the amount of sodium ion ingestion

Question 3

Why can you not just add or remove water to or from the plasma to change the plasma volume?

Answer 3

this would change osmolality which you don’t want, you just want to change the volume so you have to add or remove isosmotic solution replicating plasma in it s osmolality to change the volume

Question 4

How can you add or remove an isosmotic solution?

Answer 4

-as there are no active water pumps, you need to make water want to move so you must move osmoses and water will follow passively by osmosis

Question 5

What is transport maximum?

Answer 5

There are only a fixed number of transports in the apical membrane, when these tranporters are full at their maximum, solutes like glucose will be excreted rather than filtered hence why diabetics get glucosuria