# Homework Help: Hemodynamic help please!

1. Aug 9, 2011

### FreshlySqueez

1. The problem statement, all variables and given/known data

The red blood cell is very oddly shaped, and it is natural to wonder why it
is not spherical. This question should tell you the answer. Since the body
requires a certain minimum amount of hemoglobin in the blood (and hence a
certain minimum red cell volume), let us consider the red cell volume to be
fixed at 98 μm3.

(a) If the red blood cell were spherical, what is the smallest pore that it could
fit through? Assume that the red blood cell membrane will rupture if
stretched (a very good approximation) and remember that a sphere is the
geometrical object having minimum surface area for a given volume.

(b) Now consider the real shape of a red blood cell and allow the cell to
deform as it passes through a pore of radius R (Fig. 3.18). Assume that
the red blood cell is cylindrical with hemispherical ends. Taking cell
membrane area as 130 μm2, what is the minimum R value? You will get
a cubic equation for R; solve it numerically.

(c) Why is it advantageous to have non-spherical red blood cells?

2. Relevant equations

3. The attempt at a solution
Can't even begin since professor didn't teach anything..

2. Aug 10, 2011

### SteamKing

Staff Emeritus
If you don't follow the directions given in the problem, you won't get much help here.

You can't blame the professor if you give up without doing anything.

3. Aug 11, 2011

### Staff: Mentor

You need to look up the formula for the volume of a sphere.