W4 Fluid compartments - Jason Potas

Question 1

What is the total body water ratio between ECF and ICF?

Answer 1

40:60 ECF:ICF

Question 2

What is the intracellular ionic composition of ICF?

Answer 2

High:
K+ (major cation >120 mM) and Mg2+
HPO42- (major anion, and buffer, <100mM)
as well as anionic proteins)

Low:
Na+, Cl-, Ca2+

Electo-neutral.

Question 3

What is the ionic composition of ECF?

Answer 3

Low:
K+ and Mg2+

High:
Na+ (major cation, >120 mM), Cl- (major anion ~100mM),
Ca2+ (~2mM)

Buffer: HCO3-

Question 4

What are the two main sub-compartments of ECF?

Answer 4

interstitial fluid and plasma

Question 5

What are the rough body mass percentages of total body water in plasma, interstitial fluid, and intracellular fluid?

Answer 5

Plasma 4%; interstitial fluid 18%; intracellular fluid 38%

Question 6

What are the some special sub-compartments of interstitial fluid?

Answer 6

1. Transcellular water, such as joint fluids, intestinal fluids, cerebrospinal fluid, saliva
2. Bone water.
3. Dens connective tissue

Question 7

Which is movable and non-movable of plasma and interstitial fluid.

Answer 7

Plasma is movable, interstitial fluid is non-movable

Question 8

What is functional extracellular fluid representative of?

Answer 8

The interstitial fluid, minus the transcellular fluid, dense connective tissue, and bone water.

Question 9

What tracer is commonly used to measure plasma volume?

What could also be used?

Answer 9

Evans blue.

Any drugs that bind to albumin. However over time albumin can leak into ISF, there fore over-estimation and correction required.

Question 10

What tracer is commonly used to measure extracellular fluid volume?
What are some others?

Answer 10

Inulin.

Mannitol - as do not enter cells.
Ionics.

Question 11

How is interstitial volume calculated?

Answer 11

From ECF - plasma,

ie Inulin value - Evans blue value

Question 12

What are features of an ideal tracer?

Answer 12

1. non-toxic
2. rapidly and evenly distribute throughout the compartment.
3. not enter other compartments.
4. not be readily metabolised or excreted (or to be able to correct for this) during the equilibration period.
5. be easy to measure
6. to not interfere with body fluid distribution

Question 13

What tracer is used to measure TBW?

Answer 13

water isotopes, such as tritiated water, which slowly penetrate all compartments and can be measured with a scintillation counter.