Fluid Compartments Flashcards
What is a fluid?
A substance that deforms under a shear stress
What is a phsiologically important fluid?
Fluids in which water or fat/lipids are the solvent.
What are the key types of fluid?
- Intracellular water
- Interstitial water (filling the spaces between cells amongst the extracellular matrix)
- Fat
- Plasma
- Transcellular fluid (separate by interstitial water by a membrane)
For a 70kg person, how much is the total body water?
42L
How much of the 42L is found in each fluid type?
Plasma 3L
Interstitial fluid 10L
Transcellular fluid 1L
Intracellular 28L
What is peritoneal fluid?
fluid in abdomen
What is a haematocrit?
A measure of the proportion of the blood occupied by cells (usually 45%)
When you separate blood in a centrifuge, what order do the substances separate? (heaviest first)
RBCs
WBCs
plasma
What is the role of HCO3^- in the body?
PH regulation
What are the two ways that Ca^2+ ions exist in the body?
Half are free
Half are bound to plasma or tissue proteins
What tends to match the conc of anions in the body?
The conc of cations
Is there more extracellular or intracellular HCO3^-?
Extracellular
How can the total Ca^2+ conc be altered without changing the free Ca^2+ conc?
-Half Ca^2+ in circulation is bound to albumin which means that changing the albumin concentration changes the total Ca2+ conc without changing the free Ca2+ ion concentration
What are the destructive methods of measuring fluid compartments?
- plasma volume by exsanguination and centrifugation (not ethical)
- Total body water by weighing a body and then desiccating it then reweighing it
Explain a good way of measuring fluid body compartments
-inject a substance which is known to distribute in a given compartment and then calculate the volume of distribution (Vd)
Vd = Q/Cp
Q= amount of drug Cp= plasma conc of drug