Unit IISubject . Integrated Science

• 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.

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.

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, KSpecific Volume (V): The volume per unit mass of asubstance.• Viscosity: The internal resistance to the flow of afluid.• Mass (M): The quantity of matter contained in abody.

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 flowbehavior are fluid density and viscosity.• Density is a measure of mass per unit area (usuallyexpressed in gm/cm3) and viscosity is the magnitude of fluid resistance to flow.• One important factor affecting the density andviscosity of fluids is temperature.• As the temperature is lowered, the density andviscosity are increased.

Poisseuille's lawPoiseuille was a physician who stated:• The principle that the volume of ahomogeneous fluid passing per unit timethrough a tube is directly proportional tothe pressure difference between its endsand to the fourth power of its internalradius, and inversely proportional to itslength and viscosity of the fluid

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Factors of Resistance to Flow• In fluid flow, resistance decreases the flowrate through a pipe. Poiseuille’s Law showshow this resistance depends on threefactors:– Radius– Length– Viscosity

Three Factors of Resistance (cont…)Radius:• The larger the radius of a pipe, the greatervolume of fluid per second.• Fluid resistance decreases as pipe radius andcross-sectional area increase.Length:• Longer pipes have higher fluid resistance• Volume flow rate is inversely proportional tolength.Viscosity:• Fluid resistance increases as viscosity increases

• Blood flow– Amount of blood moving through avessel in a given time period.– Directly proportional to pressure differences, inversely proportional to resistance

Poisseuille’s Law

Poisseuille’s Law– Flow decreases when resistance increases– Flow resistance decreases when vessel diameter increases– As viscosity increases, pressure required to flowIncreases .– Flow decreases when resistance increases– Flow resistance decreases when vessel diameter increases– As viscosity increases, pressure required to flowincreases

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.

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

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.

VESSEL TYPE DIAMETER(mm) FUNCTIONAorta 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

http://en.wikipedia.org/wiki/Fluid_dynamics

ANY

Question

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