Body compartments DISTRIBUTION OF FLUIDS WITHIN THE BODY What the USMLE Requires you to Know Total Body Water what determines the Intracellular Fluid (ICF): approximately 2/3 of total of body water effective osmotic pressure Extracellular fluid (ECF): approximately 1/3 of total body water between two compa Interstitial fluid (ISF): approximately 2/3 of the extracellular fluid The changes in body Vascular fluid (VF): approximately 1/3 of the extracellular fluid (plasma plus red blood molarity and intracellular cells). A normal vascular volume is close to 5 L(blood volume) and extracellular volumes in dinically relevant situations ICF ECF measuring the volume of a I VAS The solid-line division represents the cell membrane, and the dashed line capillary membranes Flgure 1-2-1 Intracellular Fluid (ICF)versus Extracellular Fluid (ECF) These two compartments are separated by cell membranes which generally have the following important characteristics In a steady state, intracellular and extracellular osmolarity will be the same. Normally, this is cl Impermeable to Sodium( Chloride) The difference in the concentration of impermeable partides determines the osmotic move- ment of water across membranes. The concentration of these particles is often referred to as theBodyCompartments DISTRIBUTIONOFFLUIDSWITHIN THEBODY TotalBodyWater Intracellular fluid (ICF): approximately 2/3 of total of body water Extracellular fluid (ECF): approximately 1/3 of total body water Interstitial fluid (ISF): approximately 2/3 of the extracellular fluid Vascularfluid (VF): approximately 1/3 of the extracellular fluid (plasma plus red blood cells).A normal vascular volume is closeto 5 L (blood volume). rCF ECF ISF I I I I I I I I VAS I I I I I I The solid-line division represents the cell membrane, and the dashed line capillary membranes. Figure 1-2-1 IntracellularFluid(lCF)versusExtracellularFluid(ECF) These two compartments are separated by cell membranes which generally have the following important characteristics: FreelyPermeableto Water In a steadystate,intracellularand extracellularosmolaritywillbe the same.Normally,this is closeto 300mOsm. Impermeableto Sodium(Chloride) The difference in the concentration of impermeable particles determines the osmotic move￾ment of water across membranes. The concentration of these particles is often referred to as the What the USMLE !!,~~!~ to KO!! .Whatdeterminesthe effectiveosmoticpressure betweentwocompartments .Thechangesinbody osmolarityandintracellular andextracellularvolumesin clinicallyrelevantsituations .Theprinciplesinvolvedin measuringthevolumeofa bodycompartment iileilical 11