Body Fluids Flashcards
What are the two components of extracellular fluid?
What are the two components of intracellular fluid?
What two components make up the vacular component?
- ECF (40%)
- interstitial fluid and plasma water
- ICF (60%)
- cell water and RBC
- Vascular
- RBC and plasma water
Where is the major site of water ingress and egress?
Where is the major compartment for fluid water transfer?
- through the plasma water
- through the interstitial space
- direct access point for most cells
- exception = RBC and WBC
- direct access point for most cells
What is the fraction of blood that is cells? How is this information expressed?
hematocrit
expressed as a percentage (typically 40-45%)
What is the equation for blood volume?
BV = PV/ (1-Hct)
Hct = hematocrit
How is it possible that intracellular space and extracellular space have similar osmotic concentrations but different ionic compositions?
they have very similar total ionic concentratiosn (same number of ions, different identities)
osmotic concentration = total number of particles/mL (ionic or not)
major extracellular cation? anion?
major intracellular cation? anion?
- extracellular
- cation
- sodium
- anion
- bicarbonate
- chloride (major)
- cation
- intracellular
- cation
- potassium
- anion
- organic phosphate
- inorganic phosphate
- cation
Net osmotic force development
- semipermiable membrane
- movement of some solute is restricted across membrane
- water (solvent) can move freely, so it moves until concentration of the solute on both sides of the membrane are the same
What causes osmotic pressure?
As water moves to a side of more concentration, the pressure on that side increases as well. Sometimes the back pressure created by the influx of water prevents water from continuing to cross the membrane before concentrations have been equlalized
Osmotic concentration is proportional to what variable?
number of osmotic particles formed
What is the appropriate osmotic physiological concentration?
milliOsmolar units
imOSM = 10^-3 osmoles/L
What are the features of cell membranes that result in the semi-impermeable membrane?
Endothelial cell barriers specifically?
- cell membrane barriers (EC vs IC)
- charge and large size impair movement
- membrane pumps keep Na+ effectively from entering cells, thus forming a virtual barrier
- proteins can’t escape the cell interior
- Endothelial cell barriers (PV cs ISF)
- all ions can freely cross the capillary wall
- only proteins exert important net osmotic forces (oncotic pressure)
How do you measure the volume of distribution? What is this based on?
What is the adjusted equation/?
Vd = Amoutn injected/concentration
based on concentration in a well-mixed compartment
requires substance that distributes itself only in the compartment of interest
Vd= amount injected - amount excreted / concentration after equilibrium
What are the three compounds used to track total body water?
- deuterated water (D2O)
- Titrated water (THO)
- antipyrine (most common)
What are the compounds used to determine extracellular fluid volume? Why are they used?
- labeled inulin
- sucrose
- mannitol
- sulfate
They do not cross membranes well, and a pretty much excluded from cells
What are the compounds used to determine plasma volume?
- Radiolabeled albumin (most common now)
- Evans Blue Dye (which binds to albumin)
How can you estimate the ECF osmolarity through clinical laboratory measurement?
What is the equation?
Through utilizing the principle of freezing point depression, the freezing point will be more depressed with the number of solutes present
- [NA+] and anions
- [K+] and anions add slightly
- Contribution from glucose and urea normally small but real
