INTRODUCTION TO SPORT
SCIENCE
SESSION 4:
BLOOD FLOW
Contents
1) Theory (20min)
2) Practical (20 min)
BLOOD
• Blood represent approx 8% of the body
weight.
• Approx. 5.5 L in men and 5.0 L in women
• Formed of:
– Water (90%)
– Proteins
– Cells: Red blood cells (carry oxygen)
White blood cells (help fight against
disease)
Platelets (aid in clotting the blood
after a cut)
Systemic Circulation
 Oxygen rich blood is
pumped from the L atrium
 L ventricle  aorta to the
organs and tissues of the
body (except the lungs) and
then to the R atrium
 Transfer of gases, nutrients
and waste products occurs
in the capillary beds
Blood Flow
Flow = Pressure/Resistance
Blood Flow
 Volume of blood flowing through a
vessel, an organ or the entire circulation
in a given time (ml/min)
Blood Flow: Rest vs. Exercise
Flow
P
Pressure difference is the
driving force that pushes
the flow of liquid through a
pipe or blood vessel
Resistance Measure of the various
factors that hinder the
flow of liquid through a
pipe
Direction of Flow
 What happens to the air inside a
balloon if you move your fingers from
the nozzle?
 Rushes out
 Why?
 Difference in pressure between the
inside the outside of the balloon
 Air will flow from area of high pressure
to area of low pressure
Bulk Flow
 Driving force for flow is always a
pressure gradient
 Direction of flow is always down
a gradient from a region of
higher pressure to a region of
lower pressure
Pressure Gradients
 Single blood vessel represented by a tube connecting
two reservoirs containing liquid
 Pressure at either end of
the blood vessel is
determined by the vertical
distance from the vessel to
the surface of the liquid
(hydrostatic pressure)
 Difference in pressure in the 2 reservoirs produces a
pressure gradient
 Is there a pressure gradient in the example?
Role of the Heart in Generating
Pressure Gradient
 Primary function of the heart is to
generate the pressure that drives the flow
of blood through the body’s blood vessels
 By pumping blood into the arteries the
heart raises pressure in the arteries
 Creates a difference in pressure between
the arteries and veins that drives the flow
of blood
Pressure Gradients
 Pressure gradually  as
blood flows from arteries to
veins
 Blood enters the systemic
circulation at an average
pressure of ~ 90 mm Hg
 The pressure in the large
veins entering the right side
of the heart is approx 0
mmHg
 The pressure difference is 90-0 = 90 mmHg
Resistance
 Measure of the friction that blood
encounters as it passes through the blood
vessels
 Measures how difficult it is for blood to
flow between 2 points at a given pressure
difference
 Since most friction is encountered in the
peripheral (systemic) circulation it is
termed peripheral resistance (PR)
Resistance
 For a given pressure gradient a vessel
with a higher resistance yields a lower
flow
 For a given pressure difference blood
flow is greater when resistance is lower
because it is easier for blood to flow
Sources of Resistance
1. Length of the tube
2. Diameter of the tube
3. Fluids viscosity - “thickness” or
“syrupiness”
Resistance:Blood Vessel Length
 The longer the total vessel length the greater
the resistance encountered
 For the most part constant (except during
growth) blood vessels do not change in length
Resistance:Blood Vessel Diameter
 Changes in blood vessel diameter significantly alters
resistance
 Changes in resistance to blood flow in the CV system
almost always result from changes in the diameter of
blood vessels
 The diameter of blood vessels can change because
they contain smooth muscle that can relax and contract
 Relaxation of smooth muscle causes an  in vessel
radius (vasodilation) and a  in resistance
 Contraction of smooth muscle causes an  in vessel
radius (vasoconstriction) and a  in resistance
Resistance: Blood Viscosity
 Related to the thickness of a fluid
 Blood is much more viscous than water because it
contains formed elements and plasma proteins - flow
more slowly under the same conditions
 The greater the viscosity the less easily molecules
slide past one another - more difficult to get and keep
fluid moving
 Blood viscosity is fairly constant
 May be altered –polycythemia , anemia or dehydration
PRACTICAL
Effect of vessel diameter and fluid
viscosity on flow
EFFECT OF VESSEL DIAMETER AND FLUID
VISCOSITY ON FLOW
Equipment
•
Straws of different length and diamter (long and narrow
straw, short and wide straw)
•
Cocoa powder (or similar)
•
Full fat milk
•
Water
•
Container
Protocol
Fill a container with water, and another with milk with different
amounts of cocoa powder added.
Drink from the 2 glasses using the different straws.
EFFECT OF VESSEL DIAMETER AND FLUID
VISCOSITY ON FLOW - Results
What was the easiest combination?
 Long and narrow straw with milkshake?
 Short and wide straw with milkshake?
 Long and narrow straw with water?
 Short and wide straw with water?
Discussion
 Why do you think it was easier to drink
with one straw than with another?
 What were the factors affecting the flow of
milk through the straw?
Teachers Resource – Sources of Resistance
Length of the Tube:
The longer the total vessel length the greater the
resistance encountered. For the most part constant
(except during growth) blood vessels do not change in
length.
Teachers Resource – Diameter
Changes in blood vessel
diameter significantly alters
resistance
Changes in resistance to blood
flow in the CV system almost
always result from changes in
the radii of blood vessels.
Relaxation causes an  in vessel
radius (vasodilation) and a  in
resistance
Contraction causes an  in
vessel radius (vasoconstriction)
and a  in resistance.
Resistance varies inversely with
the fourth power of the vessel
radius (½ the diameter)
If the radius of a vessel is
doubled the resistance is 1/16 as
much.
The radius of blood vessel 2 fold
increases its resistance 16 (if the
pressure is held constant)
Teachers Resource - Viscosity
Related to the thickness of a fluid
Blood is much more viscous than water because it contains formed elements and
plasma proteins – flow more slowly under the same conditions.
Milkshake is similar to blood in this respect
The greater the viscosity the less easily molecules slide past one another - more
difficult to get and keep fluid moving
Blood viscosity is fairly constant.
May be altered -polycythemia, anemia or dehydration
Polycythemia is related to blood doping and in particular erythropoietin.
Ask the class to find out about erythropoietin. They should now it beneficial and
harmful effects.
Ask the class to find out about hematocrit, and explain why high hematocrit levels can
result in death
Ask the class to research blood doping, particularly in relation to cycling and distance
running
Question to pose to the class: What is the maximal hematocrit level allowed in the Tour
de France?
Why was the value set at that level?
Ask the class to determine how dehydration could increase blood viscosity