The walls of blood capillaries are permeable to water and most small molecules,
ID: 1771057 • Letter: T
Question
The walls of blood capillaries are permeable to water and most small molecules, but not to ions and large molecules like proteins. The table below gives the concentrations and molecular weights of the three major protein groups in human blood.
Substance (Concentration) (g/l) [Molecular mass] (g/mol) Albumin (45) [69,000] Globulin (25) [140,000] Fibrinogen (3) [400,000]
(a.) Find the individual, and then the total particle concentrations of these substances in mol/m3 .
(b.) Find the total osmotic pressure of these substances in Pa at normal body temperature of 37o C. [The universal gas constant is R = 8.31 J/(mol K)]. (c.) Is this osmotic pressure significant, compared to the osmotic pressure of physiological saline solution, about 8x105 Pa
Explanation / Answer
(A) Albumin concentration = concentration* 103/ molecular mass mol/m3
= 45 * 103 / 69000 = 0.6512 mol/m3
Globulin = 25 * 103 / 140000 = 0.1785 mol/m3
Fibrinogen = 3 * 103 / 400000 = 0.0075 mol/m3
Total concentration = [ 0.6512(45) + 0.1785(25) + 0.0075(3) ] / (45+25+3) = (29.25 + 4.46 + 0.022)/73 = 0.462 mol/m3
(B) Osmotic Pressure = CRT = 0.462 * 8.31 * 310 = 1190.16 Pa
Which is very much comparable to osmotic pressure of physiological saline solution.
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