Physiology Review Sheet

Body Fluid Spaces & Water Flow Across Membranes

  • Total body water (TBW)
  • 60% body weight (in men)
  • measured:
  • heavy water
  • tritiated water
  • urea
  • antipyrine
  • Intracellular fluid (ICF)
  • 40% body weight
  • measured: TBW – ECF
  • ions:
  • K+ = 140 mEq/L
  • Na+ = 10 mEq/L
  • Cl- = 10 mEq/L
  • Proteins + PO4- = 100 mEq/L
  • HCO3- = 20 mEq/L
  • Extracellular fluid (ECF)
  • 20% body weight
  • plasma + interstitial fluid (ISF)
  • measured:
  • isotopic Cl-
  • isotopic Na+
  • inulin
  • mannitol
  • ions:
  • Na+ = 140 mEq/L
  • K+ = 4 mEq/L
  • Ca2+ = 5 mEq/L
  • Cl- = 100 mEq/L
  • HCO3- = 24 mEq/L
  • Glucose = 90 mg%
  • ISF protein = 0 . . . plasma protein = 8g%
  • Plasma
  • 5% body weight
  • measured:
  • RISA
  • Evans blue
  • RBC labeled with radioactive Fe or chromium
  • ISF
  • 15% body weight
  • measured: ECF – plasma
  • Hematocrit
  • Hct = RBC vol / whole blood vol
  • 1- hct = plasma vol / whole blood vol
  • normal : 40%
  • C1V1=C2V2 (Conservation of Mass) – be able to apply!
  • Fick Principle: C1 X V(dot)1 = C2 X V(dot)2
  • - amount gained
  • + amount lost
  • takes into account time
  • Cardiac output: C.O. = V(dot)O2 / [a-v]O2
  • a: measured in any O2-rich artery (e.g. femoral)
  • v: measured in pulmonary artery
  • Pressures moving water
  • Hydraulic – from heart pumping
  • Hydrostatic – due to gravity (column of fluid)
  • Osmotic – exerted by solution that moves water down its concentration gradient (determined by amount of solute in solution)
  • Flow = Pdiff / resistance
  • Capillary exchange
  • Filtration force (pushes water and small solute out of capillaries)
  • BP
  • Combined hydrostatic and hydraulic
  • =0 in ISF and ICF
  • Absorptive force (reabsorbs water and solute into capillary)
  • Colloid osmotic pressure (COP)
  • Due to plasma proteins (albumin) that can’t exit capillaries
  • Filtration > reabsorption (slightly – excess filtrate returned to blood via lymph)
  • @ arteriolar end:
  • BP = 30 mm Hg
  • COP = 15 mm Hg
  • favor filtration
  • @ venous end:
  • BP < 30 mm Hg
  • COP > 15 mm Hg
  • May filter, may absorb
  • Starling’s Law of the capillary
  • Net fluid movement = Kf (BP – COP)
  • Osmolarity
  • Reflects total # of particles in solution
  • Π = CRT (van’t Hoff Equation)
  • Effective Π takes into account permeability (membrane must be impermeable to the solute for it to have effective Π)
  • Reflection coefficient: Πeffective/Πcalculated = σ
  • 0 = freely permeable
  • 1 = impermeable
  • Colligative properties of solution
  • Freezing point depression
  • Boiling point elevation
  • Osmotic pressure
  • Osmotic
  • # of particles in solution
  • all fluid spaces are equal! Osmolar concentration of ECF = ISF = plasma (usu 300 mOsm/L)
  • iso: same # of particles / solution volume
  • hypo: fewer particles / vol
  • hyper: more particles / vol
  • Tonicity
  • Ability to make water move in or out of a cell
  • Takes into account permeability
  • Iso: no net movement of water
  • Hypo: water moves into cell
  • Hyper: water moves out of cell
  • Permeabilities
  • Na+, Cl-, K+, Ca2+ : impermeable
  • Glucose: so slow, may as well be impermeable
  • Urea: freely permeable
  • NH4: not permeable, but in equilibrium with NH3 which is moderately permeable
  • Sweat
  • Hyperosmotic volume contraction
  • Osmolarity of ECF ↑
  • ECF volume ↓
  • Water shifts out of ICF  ICF osmolarity↑ & ICF vol ↓
  • Plasma protein concentration ↑, but hct doesn’t change (water shifts out of RBC to offset concentrating effect of ↓ ECF vol)
  • Hemorrhage
  • Isosmotic volume contraction
  • ECF volume ↓, but no change in osmolarity
  • Change in Starling forces due to ↓ BP allows movement of ISF into capillaries which dilutes hct and COP
  • Vol% = Vol / 100 mL
  • WATCH UNITS!