3.24 The purpose of this question is to investigate the implications of Fig. 3.1

Question

3.24 The purpose of this question is to investigate the implications of Fig. 3.16. Specifically, we wish to determine how the feed reservoir hematocrit changes as a function of time in the experiment shown in Fig. 3.14. Suppose that at time zero the total blood volume in the feed reservoir is Vo, and that the feed reservoir hematocrit is Hfo. Further, suppose that blood is pumped from the feed reservoir through a capillary at a constant volumetric flow rate (a) Show that the feed reservoir hematocrit changes with time, t, according to the equation (3.54) where HR is the tube relative hematocrit. Hint: start from the statement VRBC HV in the (3.55) where VRBc is the volume of red cells in the feed reservoir, and Vp is the volume of plasma in the reservoir Integration of the above equation shows that the hematocrit eventually approaches 100% in the feed reservoir, why does this not occur in the circulatory system: that is, why does the red cell count not increase to sornething close to 100% at the entrance to the capillaries? You do not need to use any mathematics; a description in words (plus a simple sketch if you prefer) will do the job. (b)

Explanation / Answer

1,As blood flow from the arterioles into the capillaries a change in pressure occurs. In order to maintain pressure, the capillaries branch off to a web of vessels that carry blood into the venules.

2,Through this process blood undergoes micro-circulation. In micro-circulation, the Fahraeus effect will take place, resulting in a large change in hematocrit. As blood flows through the arterioles, red cells will act a feed hematocrit (Hf), while in the capillaries a tube hematocrit (Ht) occurs.

.3, In tube hematocrit plasma fills most of the vessel while the red cells travel through in somewhat of a single file line. From this stage, blood will enter a the venules increasing in hematocrit, in other words the discharge hematocrit (Hd).

In large vessels with low hematocrit, viscosity dramatically drops and red cells take in a lot of energy. While in smaller vessels at the micro-circulation scale, viscosity is very high. With the increase in shear stress at the wall, a lot of energy is used to move cells.

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