USMLE Step 1: Physiology Changes in Volume and Concentration(dashed lines) 1. Loss of isotonic fluid that might be due to hemorrhage(neglect loss of intracellular fluid as RBC volume), isotonic urine, or the immediate consequences of diarrhea or vomiting Figure 1-2-3 There will be a loss of volume but no change in extracellular effective osmolarity. The fact that extracellular osmolarity is unchanged means no change in intracellular volume 2. Loss of hypotonic fluid that might be due to sweating(dehydration), hypotonic urine, or -2-4 Losing hypotonic fluid from the extracellular space would increase extracellular effective osmolarity(sodium concentration would increase). Fluid would move from the intracel- lular to the extracellular compartment until osmolarity was again equal in the two com- partments. The fluid entering the extracellular space would partially but not completely compensate for the originate insult. edical/' USMLEStep1: Physiology 14 meCtical ChangesinVolumeandConcentration(dashedlines) 1. Lossof isotonicfluidthat mightbe due to hemorrhage(neglectlossof intracellularfluid as RBCvolume),isotonicurine,or the immediateconsequencesof diarrheaor vomiting: Figure 1-2-3 There willbe a loss of volume but no change in extracellular effectiveosmolarity. The fact that extracellular osmolarity is unchanged means no change in intracellular volume. 2. Loss of hypotonic fluid that might be due to sweating (dehydration), hypotonic urine, or diabetes insipidus: : - - - - - - - - - - - - -1- - - - - --: "I I I I I I I I I Figure 1-2-4 Losing hypotonic fluid from the extracellular space would increase extracellular effective osmolarity (sodium concentration would increase). Fluid would move from the intracel￾lular to the extracellular compartment until osmolarity was again equal in the two com￾partments. The fluid entering the extracellular space would partially but not completely compensate for the originate insult