Renal Phys - Body Compartments

Question 1

How do you calculate Total Body Water (TBW)?

Answer 1

Total Body Water is 60% of body weight

TBW = 0.6 x body weight

Question 2

What is the fluid distribution in the body?

Answer 2

40% of Total Body Water (TBW) is Intracellular Fluid (ICF)

20% of TBW is Extracellular Fluid (ECF)

25% of ECF is Plasma

75% of ECF is Interstitial Fluid

Question 3

What is third spacing?

Answer 3

When fluid enters a space in the body it shouldn’t:

Between organs in the abdomen or interstitial area around lungs (due to pulmonary edema)

Third spacing is problematic

Question 4

What are the prominent cation(s) in the ECF?

Answer 4

Na+

Question 5

What are the prominent anion(s) in the ECF?

Answer 5

Cl- (and HCO3- to a lesser extent)

Question 6

What are the prominent cation(s) in the ICF?

Answer 6

K+, Mg2+

Question 7

What are the prominent anion(s) in the ICF?

Answer 7

PO4(3-) and protein anions to a lesser extent

Question 8

What is the Gibbs-Donnan Effect?

Answer 8

Cell membranes are impermeable to proteins, but cells contain large quantities of negatively charged proteins.

Cells are permeable to ions

Large quantity of negatively charged proteins in a cell provides both an oncotic gradient and electrochemical gradient favoring the movement of positively charged ions into the cell.

Question 9

What counter-acts the Gibbs-Donnan Effect and what would happen if it did not occur?

Answer 9

N/K-ATPase pump counteracts the Gibbs-Donnan effect by pumping 3 Na+ ions OUT of the cell while pumping 2 K+ ions into the cell.

If this ATPase action were not present, the cell would continuously bring in water causing it to eventually lyse due to swelling.