For the following clinical scenario, predict the possible effect on a patient’s
ID: 51678 • Letter: F
Question
For the following clinical scenario, predict the possible effect on a patient’s erythrocytes. You need to memorize that the osmolarity of an erythrocyte (and the human body in general) is 300mOsm. Justify your answers by:
A. Calculating mM for ICF and ECF
B. Calculating mOsM for ICF and ECF
C. Determine the osmolarity of the solution
D. Determine the tonicity
E. Determine the permeability of the solute (permeable or impermeable)
F. Determine if diffusion is occurring and in what direction
G. Determine if osmosis is occurring and in what direction
SCENARIO:
1. A patient is administered an IV (intravenous) solution of 0.9% Na+ Cl- (called normal saline, NS), which is approximately isotonic to erythrocytes.
Explanation / Answer
ANSWERS
A. It is not mM but it is mOM . For both ICF and ECF is 300mOM.
B. The mOsm for both ICF and ECF is 300mOsm.
Explanation
Addition of an isotonic NaCl solution (e.g., intravenous infusion of 0.9% NaCl)to the ECF increases the volume of this compartment by the volume of fluid administered. Because this fluid has the same osmolality as ECF and therefore also ICF, there is no driving force for fluid movement between these compartments, and the volume of ICF is unchanged.
C. The osmolarity of the solution of 0.9% NaCl (Normal Saline) is 0.308 Osmolar.
Calculation
D. Tonicity: The net movement of water into or out of the cell is driven by differences in osmotic pressures between the extracellular fluid and the intracellular fluid.
If a cell placed in an isotonic solution (NaCl) no change will occur. Since, NaCl is an isotonic solution nothing will happen.
E. NaCl is impermeable.
Explanation
The cell membrane that surrounds the RBC is a semipermeable membrane that can only allow diffusing some of the smaller and uncharged molecules and watering across the membrane. However, the solutes like NaCl, glucose etc., that are dissolved in water cannot pass through the lipid bilayer of the cell membrane, and thus cannot move across the cell membrane even if there is a difference in concentration.
F. No Diffusion occurs because NaCl is an isotonic solution.
G. No Osmosis occurs also because NaCl is an isotonic solution that does not show any difference in Osmolarity in ICF and ECF.