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MCAT Review Problem #9
Use the following to answer questions 1  6:
Human blood varies substantially from person to person, with state of
health, etc. Typical values of the density of blood plasma and blood
cells are 1025 and 1125 ,
respectively. The viscosity of blood at C is about 2.7
centipoise, much greater than the viscosity of water at the same
temperature (about 0.7 centipoise). The flow of blood in the human
circulatory system, which consists of nearly circular cross section
blood vessels, can be described quite well using Poiseuille's
equation:
V/t is the volume of blood flow per unit time, is the
pressure difference between the ends of a tube of radius R and
length L. is the fluid's coefficient of viscosity, or more
simply the viscosity.
 What is the mass of 500 ml of blood plasma which has a density of 1025 ?
 205 g
 488 g
 512 g
 762 g
 What is the apparent weight (i.e., net downward force) on a blood cell of volume 150 and density 1125 suspended in plasma of density 1025 ? ( )
 0.15 pN
 0.30 pN
 0.45 pN
 0.60 pN
 When blood moves from a blood vessel with diameter 5.0 mm to a blood vessel of diameter 3.0 mm, the speed of flow increases by a factor of
 1.3
 1.7
 2.0
 2.8
 According to Bernouilli's law the concentration of blood cells is greater near the center than near the wall of a blood vessel because
 both the fluid speed and pressure are lower near the center.
 the speed is greater but the pressure is lower near the center.
 the speed is smaller but the pressure is greater near the center.
 both the fluid speed and pressure are greater near the center.

The viscosity of a fluid can be determined by measuring the time taken
for a given volume of the fluid to flow through a fixed length of
capillary tube of fixed radius. The pressure difference is the fluid
static pressure difference over the height of the tube. According to
Poiseuille's equation, the relative flow time for a liquid of density
d in this type of viscometer is directly proportional to
 the viscosity.
 the viscosity divided by the density.
 the viscosity times the density.
 the density divided by the viscosity.

According to Poiseuille's equation, the volume of blood flow per unit
time is reduced to what percent of the initial value when the blood
that was flowing in a 5.0 mm diameter blood vessel enters a 3.0 mm
diameter blood vessel, the pressure difference per unit length
remaining constant?
 13 %
 22 %
 36%
 50 %
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Katherine Benson
Sat Oct 30 15:51:51 EDT 1999