2. • Define key terms
• Describe basic properties of fluid
• Discuss Poiseuille’s law
• Apply Poiseuille’s law to blood
flow
• Discuss other physiological
application of
Poiseuille’s law.
3. Properties of Fluid
o A fluid is any substance which flows because its
particles are not rigidly attached to one
another.
o Fluid includes Liquid and Gas
o Some properties of fluids include
o Pressure, Temperature, Volume, Viscosity,
Density, and Mass.
4. Properties of Fluid (cont..)
• Pressure (P): The force per unit area.
Unit: pounds per square inch (psi).
• Temperature (T): The relative measure of
hotness or coldness of a body.
Units: oC, oF, K
Specific Volume (V): The volume per unit mass
of a
substance.
• Viscosity: The internal resistance to the flow
of a
fluid.
• Mass (M): The quantity of matter contained in
a
5. Properties of Fluid (cont..)
• Density (D): Mass of a substance per unit
volume.
Unit is Kg/m3 or gm/cm3
• The two main fluid parameters that influence
flow
behavior are fluid density and viscosity.
• Density is a measure of mass per unit area
(usually
expressed in gm/cm3) and viscosity is the
magnitude of fluid resistance to flow.
• One important factor affecting the density and
viscosity of fluids is temperature.
• As the temperature is lowered, the density and
6. Poisseuille's law
Poiseuille was a physician who stated:
• The principle that the volume of a
homogeneous fluid passing per unit time
through a tube is directly proportional to
the pressure difference between its ends
and to the fourth power of its internal
radius, and inversely proportional to its
length and viscosity of the fluid
7. 7
Factors of Resistance to Flow
• In fluid flow, resistance decreases the flow
rate through a pipe. Poiseuille’s Law shows
how this resistance depends on three
factors:
– Radius
– Length
– Viscosity
8. Three Factors of Resistance (cont…)
Radius:
• The larger the radius of a pipe, the greater
volume of fluid per second.
• Fluid resistance decreases as pipe radius and
cross-sectional area increase.
Length:
• Longer pipes have higher fluid resistance
• Volume flow rate is inversely proportional to
length.
Viscosity:
• Fluid resistance increases as viscosity
increases
9. • Blood flow– Amount of blood moving through a
vessel in a given time period.
– Directly proportional to pressure differences,
inversely proportional to resistance
Poisseuille’s Law
10. Poisseuille’s Law
– Flow decreases when resistance increases
– Flow resistance decreases when vessel diameter
increases
– As viscosity increases, pressure required to flow
Increases .
– Flow decreases when resistance increases
– Flow resistance decreases when vessel diameter
increases
– As viscosity increases, pressure required to flow
increases
11. To Respiratory System:
Flow to and from the alveoli depends on:
a) the resistance (R) to flow offered by the
airways (reflecting their size), and
b) the pressure generated (ΔP) by the
respiratory pump muscles / Intercostals
muscles.
12.
13. water (0 °C) 1.8
water (20 °C) 1.0
water (100 °C) 0.3
white blood (37 °C) 4
blood plasma (37 °) 1.5
engine oil (AE10) 200
air 0.018
14. Home activity
Make a sloppy mixture of corn flour and water. Slowly
move your hands through the mixture. Also, hit the
mixture with your finger quickly.
15. VESSEL TYPE DIAMETER(mm)
FUNCTION
Aorta 25 Pulse dampening and distribution
Large Arteries 1.0 - 4.0 Distribution of arterial blood
Small Arteries 0.2 - 1.0 Distribution and resistance
Arterioles 0.01 - 0.20 Resistance (pressure & flow
regulation)
Capillaries 0.006 - 0.010 Exchange
Venules 0.01 - 0.20 Exchange, collection, and
capacitance
Veins 0.2 - 5.0 Capacitance function (blood volume)
Vena Cava 35 Collection of venous blood
