Homeostasis - Rao Flashcards
What is the relationship between %TBW and fat content?
The % body weight of TBW decreases as fat content increases.
What are the mechanisms of water intake and their respective amounts?
Oxidation of carbohydrates (300 ml/day)
Drink/Food (2200 ml/day)
What are the mechanisms of water output and their respective amounts?
Urine (500-20,000 ml/day)
Perspiration of skin and lung (700 ml/day up to 5 L/day in burn victims)
Sweat (100 ml/day up to 1-2 L/day w/ exercise)
Feces (100 ml/day or more with diarrhea)
What is total body water?
40-42 L
What is the volume ICF? ECF?
ICF - 25 L
ECF - 15 L
What are the subsets of ECF and their respective volumes?
Plasma - 3 L (high protein content)
Interstitial Fluid - 12 L (low protein content)
What is total blood volume?
5 L
60% plasma - 40% hematocrit
What two compartments have similar ionic composition?
Plasma and interstitial fluid (ISF)
What are the major cations and anions of ECF (plasma/ISF)?
Cation - Na
Anion - Cl, bicarbonate
Na > Cl in plasma due to Gibbs Donnan effect
What are the major cations and anions in ICF?
Cation - K
Anion - Protein, bicarbonate, phosphate
Mg and PO4 are higher in which compartment?
ICF
Calcium is present in which compartment?
ECF
How do you calculate the volume of body fluid compartments?
Dilution principle
Volume = Quantity Injected / (Measured Concentration) = Q / (Q/V)
What substances do you use to measure plasma volume?
131I-albumin
Evans blue dye
What is an equation relating blood volume to plasma volume?
BV = PV / (1 - hematocrit)
What substances do you use to measure extracellular fluid volume?
Inulin
Thiosulfate
Na
What is an equation that relates interstitial fluid volume and extracellular fluid volume?
ICF = ECF - PV
How do you correct for loss of probe in urine?
Subtract urine output from initial quantity administered
What substance do you use to measure total body water?
Deuterated water
Tritiated water
Antipyrene (lipid soluble)
What is the driving force of fluid movement between plasma and ISF?
Filtration - Starling forces (hydrostatic / oncotic pressure)
What is the driving force of fluid movement between ICF and ECF?
Osmosis - Na
How many osmoles are each of the following in 1 L solution:
1 mole glucose
1 mole NaCl
1 mole Na2SO4
Glucose - 1 osmole
NaCL - 2 osmole
Na2SO4 - 3 osmole
Define osmotic pressure.
Amount of pressure required to prevent osmosis.
Convert 1 mOsmole to mm Hg
1 mOsmole = 19.3 mmHG
What are the effects of dehydration in volume and osmolarity?
Volume - decrease in all compartments
Osmolarity - increase in all compartments
What is a good estimate of plasma osmolarity?
Plasma osmolarity = [plasma Na x 2] + glucose + urea
What is considered an abnormal osmolarity gap?
> 10 mOsmole difference between measured and estimated values
What are the effects of an isotonic infusion (saline) in volume and osmolarity?
Volume - increase in ECF
Osmolarity - no change in either compartment
What are the effects of gain of water in volume and osmolarity?
Volume - increase in all compartments
Osmolarity - decrease in all compartments
What are the effects of gain of salt in volume and osmolarity?
Volume - increase ECF; decrease ICF
Osmolarity - increase in all compartments
What are the effects of loss of salt in volume and osmolarity?
Volume - decrease ECF; increase ICF
Osmolarity - decrease in all compartments
What are the effects of an isotonic urea infusion in volume and osmolarity?
Volume - increase in all compartments
Osmolarity - no change in either compartment
