Body Fluids Flashcards
What is the typical volume of body fluid in a 70kg man?
42L
Of the 42L body fluid, what volume is in the extracellular compartment?
14L
What volume is in the intracellular compartment?
28L
What are the 3 sub-compartments of the extracellular compartment?
Plasma, interstitial fluid, transcellular fluid
What volume of fluid is in the plasma?
3L
What volume of fluid is in the interstitial space?
10L
What is the volume of transcellular fluids?
1L
What are some examples of transcellular compartments?
Peritoneal space, CSF, Synovial fluid
Definition of haematocrit
A measure of the proportion of blood occupied by cells (45%)
What protein is about 50% of Ca2+ in circulation bound to?
Albumin
What form of Ca2+ is biologically active?
Free Ca2+
What form of Ca2+ does the body regulate?
Free Ca2+
Definition of ‘volume of distribution’
The volume of fluid required to contain the total amount of drug in the body at the same concentration as that present in plasma
What is the equation for volume of distribution?
Vd = Q (amount of drug) / Cp (plasma concentration of drug)
What is the volume of distribution of Heparin for a 70kg person?
3.5L
What is the volume of distribution for Gentamicin?
14-28L
How can total body water be measured?
Using isotopes of water (deuterium oxide or tritiated water)
How can plasma volume be measured?
Substance used that must remain confined within the vascular space (i.e. does not cross the capillary endothelium)
What substance is used to measure Plasma volume?
Evan’s Blue - binds to plasma albumin
Definition of Osmolality
Number of osmoles per unit mass of solvent (Osm/kg)
Definition of Osmolarity
Number of osmoles per unit volume of the solution (Osm/L)
What is the difference between Isotonic and Isosmotic?
Isosmotic solutions - same osmolarity
Isotonic solution - applying the solution to cells will not cause net fluid movement
What is the example of a solution which is isosmotic with intracellular fluid but not isotonic?
Urea
Why is urea not isotonic with intracellular fluid?
Urea crosses freely across plasma membranes, so will enter the cells, increasing intracellular osmotic pressure
What causes plasma albumin levels to fall?
Liver failure, renal failure
What are the effects of a fall in plasma albumin levels?
Pulmonary/peripheral oedema, ascites
How are osmotic pressure changes corrected?
Using mannitol
How does mannitol work?
Increases the plasma and extracellular space osmolality, so pulls water from the intracellular and transcellular spaces (CSF)
What is mannitol used for?
Decrease intracranial pressure
