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 do you determine compartments with no compartment-specific substance?
Provide 2 examples
It is determiend by subtraction
- intracellular fluid volume (ICFV)
- ICFV = TBW - ECFV
- interstitial fluid volume (ISFV)
- ISFV = ECFV - PV
What are the controlled and regulated variables involved in body water distribution?
Which variable is kept in a steady state?
- body controls ingestion adn excretion to regulate:
- constant total body water (volume regulation)
- constant total body osmolarity (osmoregulation)
- steady state: osmolarity will be identical in all body fluid compatments
- body water will redistribute to accomplish this
What is the only thing that can change ICF volume?
ECF osmolarity
ICF volume is NOT altered by changes in ECF volume that are iso-osmotic (isotonic)
What is the ICF reaction to an increase in ECF osmolarity?
- water moves out of cells
- ICF volume decreases (cells shrink)
- ICF osmolarity increases (increas in [electrolytes])
- total body osmolarity remains highter than normal
What proxy measurement is plasma osmolarity used for? Why is plasma osmolarity used?
ECF osmolarity
plasma is clinically accessible
ECF osmolarity can be roughly estimated as
Posm = 2 [NA+]p
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
What is effective osmolarity?
waht is an example of an ineffective osmole?
the portion of osmolarity that influences water movement
urea is not an effective osmole, it moves across membranes almost as easily as water, so it does not influence water movement
Can you add amounts? Can you add volumes? Can you add concentrations?
What equation can you use to solve infusion problems?
amounts: yest
volumes: yes
concentrations; no
C’ = A + A’ / V + V’
What is the name for solutions where there is:
no change in ICFV?
Decrease in ICFV?
Increase in ICFV?
Provide examples of each
- No change: isotonic
- D5W
- glucose rapidly metabolized to CO2 and H2O
- eventually become hypotonic
- Saline
- .9% NaCl “normal”
- D5W
- decrease: hypertonic
- saline
- 5% NaCl
- saline
- increase: hypotonic
- saline
- 0.2% NaCl
- saline
Why might you give a patient a saline + dextrose solution?
available in many concentrations
used for simultaneous volume replacement and caloric supplement
Why might you give a patient a dextran solution?
dextran is a long chain polysaccharide that is confined to the vascular compartmet
it is used to expand plasma portion of ECF to support cardiovascular function
