F L U I D & E L E C T R O L Y T E B A L A N C E

Question 1

what are the compartments of ICF and ECF, and how can they be normalized for homeostasis?

Answer 1

ICF: 25L - 40% body weight
ECF: 15L - 20% body weight
-interstitial fluid 12L (80% ECF)
-plasma 3L (20% ECF)

osmosis eliminates minor differences in concentration
- because cell membranes are permeable to water

Question 2

how can sodium and potassium be excreted in urine?

Answer 2

ANP causes Na+ loss at kidneys

secretion of K+ at DCT or CD (due to high K+ in ECF) causes K+ loss at kidneys

Question 3

describe how buffers minimize changes in the pH of body fluids

Answer 3

excrete more H+ by buffering with anion before excretion (HCO3-)

H2O + CO2 H2CO3 H+ + HCO3-

Question 4

discuss how and why fluid shifts occur between ICF and ECF

Answer 4

if water is lost, but electrolytes retained:

• ECF osmotic concentration rises
• becomes hypertonic to ICF
• Fluid shifts from ICF (cells) to ECF (blood, interstitial)
• May result in dehydration

if water is gained, but electrolytes are not:

• ECF volume increases
• ECF becomes hypotonic to ICF
• fluid shifts from ECF to ICF (into cells)
• may result in overhydration