Session 4

Question 1

How does sodium in the ECF affect blood pressure?

Answer 1

• Major osmotically effective solute in the ECF is Na+ • Water in the ECF compartment DEPENDS on the Na+ content • If Na+ in ECF changes then volume of ECF changes • Change the Na+ results in affect on ECV • Thus BP

Question 2

Why does Na+ excretion need to vary?

Answer 2

• Ingestion of sodium can vary (low salt diet 0.5 g/d to 20-25 g/d) • Kidney Na+ excretory rates must vary over wide range depending on diet • Match excretion to ingestion • Urinary water excretion can be varied physiologically by the kidney

Question 3

Why not just add or remove water to or from the plasma

Answer 3

. because that would change the plasma osmolarity

Question 4

How do we add or remove an isosmotic solution?

Answer 4

• No active water pumps, need to make water want to move • The answer is therefore to move osmoles and water will follow

Question 5

What needs to be added to ECF to increase its volume?

Answer 5

• Need to add isosmotic solution to increase volume • or remove and isosmotic solution to reduce volume without changing osmolarity