Question

1. A normal individual has within their body 14L of Extracellular fluid and 28 L of Intracellular fluid and of course the normal mOsMolarity is 300. (From this you should be able to get the total body, ECF, and ICF: solute (mOsmoles), volume, and mOsMolarity During a very hot marathon, a runner drank 4.5 Liters of distilled water (not a good idea during a marathon). Because it was so hot, she also produced 3 L of perspiration containing 0.3% of NaCl which is assumed in this example to be non-penet srating.

a. Convert 0.3% NaCl (58.4grams/mole) to mOsM (milliosmolar) – you will need this for Question 1b.

b. Calculate the solute (mOsmoles), volume, and mOsMolarity in the runner after she completed her marathon for Total Body, ICF and ECF

Answer 1

a)0.3% Nacl means 0.3 g Nacl in 100 ml solution.

So in 1 liter of solution ,3 g Nacl.

Number of millimoles in 3 g Nacl =(3/58.4)*1000= 51.3 mOsm/L

b)

Before the marathon,

ECF=14 L & ICF=28 L

Usually plasma constitutes 25% of the volume of ECF.

So volume of plasma =3.5 L

Number of solutes = 3.5 * 300 =1050 mOsm

After drinking 4.5 L distilled water, volume is plasma =3.5+4.5 =8 L

But number of solutes remain the same.

Then she lost water and solutes in sweat.

Volume of plasma after sweating =8-3=5 L

Number of solutes lost = 51.3 *3=153.9 mOsm

Number of solutes left=1050-154= 896 mOsm

So milliosmolarity = 896 /5 = 179.2 mOsm/L