Red blood cells with an internal osmolarity of 300 mOsM are placed in the follow

Question

Red blood cells with an internal osmolarity of 300 mOsM are placed in the following solutions. Designate each solution according to its smolarity andtonicity, and explain what happens to the cells (no change, shrink, swell) and why. (hint- urea is a penetrating solute). 1. a) 300 mOsM urea b) 300 mOsM NaCI c) 200 mOsM urea plus 300 mOsM NaC d) 400 mOsM NaCI 2. The following figure shows schematic diagrams of two cells that have the same volume but quite different shapes. One cell (left panel) is spherical, the other is approximately cylindrical but contains a large number of microvilli. The cell membranes have the same conductivity to water. If the two cells are placed in a hypotonic solution, which cell swells more rapidly? Explain your answer. Show equatiorn 3. The rationale behind intravenous fluid therapy depends on an understanding of osmolarity and tonicity. Fill in the chart below to show what would happen to the volumes and osmolarities of the intracellular (ICF) and extracellular (ECF) compartments when the solutions at the left are administered to a person whose body osmolarity is 300 mOsM. Use up and down arrows for increase and decrease and n/c for no change, Assume that instantaneous equilibration takes place. ECF volume volume osmolarity osmolarity ICF ICF ECF 200 mOsM NaCI 300 mOsM urea 100 mOsM urea AND 200 mOsM NaCI 300 mOsM NaCI 4. An individual with a body weight of 75 kg is injected with 8mls of Evans blue dye (10mg/ml). After 10 minutes, a blood sample is withdrawn and found to contain 0.032 mg/ml of Evans blue dye. a) What is his the plasma volume? lf the plasma volume represents 8% of the total body fluid volume estimate the volume of the: b.) Interstitial space c.) Intracellular space d.) Total fluid volume of individual?

Explanation / Answer

1. Given internal osmolarity of red blood cell = 300 mOsm

a) 300 mOsm of urea- Urea is a penetrating solution but osmolarity being same inside and outside, it is a isotonic solution. It is also an isoosmotic solution, concentration of urea being same inside and outside the cell.So, no osmosis will take place or the amount of exosmosis is counterbalanced by same amount of endosmosis. So , no change in size of cell.

b) 300 mOsm NaCl - NaCl is considered to be non-penetrating solution for red blood cells. NaCl dissociates into sodium and chloride ions in solution. So, its osmotic pressure or osmolality is double of its concentration. So, externally it can be said to be hyperosmotic but as it is isotonic. No change in Size of cell.

c) 200 mOsm urea plus 300 mOsm NaCl - Considering the total concentration of the solution it is hypoosmotic and hypertonic. At first cell will shrink due to outside hypertonic solution, then urea will penetrate and enter the cell and decrease its rate of shrinkage a little but overall it will remain shrinked as concentration of non penetrating NaCl is greater outside.

d) 400 mOsm NaCl - As is seen from the concentration, it is a hyperosmotic solution, and is hypertonic. Cell will shrink.

2. Cylindrical cell with microvilli will swell more rapidly than spherical cell due to its larger surface area of absorption.

The equation is

dn/dt = P x A x dc/dx, where, dn/dt = rate of diffusion, P= Permeability of the membrane, A= Surface area, dc/dx = concentration gradient.

3.

4. It is given by the equation

C= M/V, where C= concentration of dye, M = Mass of the body, V= Volume

Putting C= 0.032 mg/ml, M= 75 kg = 75 x 106 mg,

V = M/C= 75 x 106 mg,/0.032 mg/ml = 2,343.75 x 106 ml

Let the total body fluid volume be x ml. So, 8x/100 =  2,343.75 x 106 ml

Therefore, x = 29,296.875 x 106 ml

For interstitial fluid volume calculation we need a dye which is cell impermeant like inulin or mannitol.

ECF volume ICFvolume ICF osmolarity ECF osmolarity 200 mOsm NaCl decrease increase n/c increase 300 mOsm urea
n/c n/c increase decrease 100 mOsm urea and 200 mOsm NaCl
n/c n/c increase increase more than ICF 300 mOsm NaCl
n/c n/c n/c increase

Related Questions

Navigate

• Browse (All)
• Browse R
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.