Fluid and Salt Balance

Question 1

What is the total body water?

Answer 1

42 litres (0.6 x body weight)

Question 2

What is the total intracellular fluid?

Answer 2

28 Litres (0.4 x body weight)

Question 3

What is the total extracellular fluid?

Answer 3

14 litres (0.2 x body weight)

Question 4

What can extracellular fluid be divided into?

Answer 4

1. Plasma (3.5L)

2. Interstitial fluid (10.5L)

Question 5

What does the extraceullar fluid contain in terms of ions?

Answer 5

Na+, K+, Cl-, HCO3-

Question 6

What is osmolarity?

Answer 6

(Na+ + K+) x 2 = (145 + 4) x 2 = about 300 milliosmoles/litre

Question 7

How much water do we gain and lose a day?

Answer 7

2.5L/day

Question 8

What is hypovolaemia?

Answer 8

A decrease in circulating blood volume

Question 9

What senses the changes in circulating blood volume and causes the release of angiotensin II?

Answer 9

Baroreceptors

Question 10

What is hypertonicity?

Answer 10

When blood osmolarity increases (dried out cells)

Question 11

What sense the changes in blood osmolarity?

Answer 11

Osmoreceptors

Question 12

What does the hypothalamus do in times of hypovolaemia or hypertonicity?

Answer 12

Cause vasopression (anti-diuretic hormone) release from the posterior pituitary and also thirst

Question 13

What receptors does ADH (vasopressin) act on?

Answer 13

V2 receptors

Question 14

What happens when ADH binds V2 receptors?

Answer 14

Activates adenylate cyclase to convert ATP to cAMP

Question 15

What does an increase in cAMP lead to in cells with V2 receptors?

Answer 15

Insertion of aquaporin into the cell membrane which lets water in to return the cell to normal from hypertonic

Question 16

What is retained in order to retain water?

Answer 16

Sodium ions