Water & Electrolye Balance

Question 1

Describe the electrolyte composition of each fluid compartment

Answer 1

ICF - water, urea, sodium, potassium
Interstitial fluid - water, urea, sodium, potassium
Plasma - water, urea, sodium, potassium, plasma protein

Question 2

Explain the processes by which electrolytes and water move between body fluid compartments

Answer 2

Osmotic, oncotic pressures
Hydrostatic pressure
Diffusion
Facilitated diffusion
Active transport
Vesicular transport

Question 3

Explain the renal mechanisms for the regulation of extracellular fluid volume and composition

Answer 3

RAAS –> vasoconstriction, sodium and water retention etc.

Question 4

Describe the thirst response

Answer 4

Increased osmolality of plasma –> low saliva –> dry mouth/osmoreceptors in hypothalamus –> hypothalamic thirst centre
Low plasma volume –> low BP –> JG cells in kidney –> RAAS –> increased AT2 –> hypothalamic thirst centre

Question 5

Describe the electrolyte and water composition of the commonly used IV fluids

Answer 5

Water - 5% dextrose
Saline - 0.9% sodium chloride
Colloid

Question 6

State the percentage of body weight accounted for by water in adult males and females

Answer 6

Males - 60%

Females - 50%

Question 7

Describe the main fluid compartments of the body and list the normal volumes of each

Answer 7

ICF - 25L, 40% tbw

ECF (interstitial fluid, plasma) - 15L, 20% tbw