1) A fluid is a substance that does not support shear stress and takes the shape of its container. Shear stress occurs when parallel forces cause one part of a body to slide over another. 2) Laminar flow occurs in parallel layers with no disruption, while turbulent flow is characterized by random, chaotic property changes and mixing of fluids. Laminar flow can transition to turbulent flow by increasing fluid flow rate, decreasing tube radius, or decreasing fluid viscosity. 3) Blood pressure is measured as systolic (ventricular contraction) and diastolic (ventricular relaxation) using a sphygmomanometer. Vasoconstriction and vasodilation help regulate blood pressure by decreasing or increasing vessel

2. WHAT IS A FLUID???
In a mechanical view, a fluid is a substance that does not support shear stress that is why a
fluid at rest has the shape of its containing vessel. A fluid at rest has no shear stress.
WHAT IS SHEAR STRESS???
If the applied load consists of two equal and opposite parallel forces which do not share the
same line of action, then there will be a tendency for one part of the body to slide over, or
shear from the other part.
In the figure below, if the section LM is parallel to the forces and has an area A, then
the average Shear Stress . S=
𝑭
𝑨

3. LAMINAR VS TURBULENT FLOW

4. Laminar flow or streamline flow occurs when a fluid flows in
parallel layers, with no disruption between the layers (no mixing of
fluids). Laminar flow tends to occur at lower velocities.
Turbulent flow is characterised by random chaotic property
changes.(mixing of fluids, collision of fluid particles)
Note: laminar flow can be turned into turbulent flow by:
1) Increasing amount of fluid per cross section per time
2) Decreasing the radius of the medium
3) Decreasing the viscosity of the fluid

5. BLOOD PRESSURE MEASUREMENTS
TYPES OF BLOOD PRESSURE:
Systolic: contraction of the ventricles
Diastolic: relaxation of the ventricles
Normal blood is about 𝟏𝟐𝟎
𝟖𝟎 𝑯𝒈𝒎𝒎
Blood pressure is measured using the sphygmomanometer
````````````````````````````````````````````````````````````````````````````````` Kortoff’s sound
Note: blood pressure is measured in the large arteries
Pressure Sound Flow type
P> systolic
pressure
silence No flow
Sys>P> diastolic Oscillating sound Turbulent flow
Diastolic>
pressure
No sound Laminar flow

6. REGULATION OF BLOOD PRESSURE
vasoconstriction and vasodilatation are an important part of controlling blood
pressure.
They're probably not the most important part - as we'll see next - but inevitably
they play their role.
As the blood vessels constrict, there is less room for the blood to go through
and so the pressure goes up; both the systolic blood pressure and diastolic
blood pressure will be increased.
Conversely, as the vessels dilate, there is more room for the blood to go
through, and so the pressures go down.

8. Ideal Fluids
 Ideal fluid; a fluid with no friction
 Also referred to as an inviscid (zero viscosity) fluid
 Fluid is incompressible (isochoric flow)
 Ideal fluids are just theoretical and do not really exist
Real Fluids
 Particles are constantly interacting
 Thus, fluid friction is created
 Shear forces oppose motion of one particle past another
 Friction forces gives rise to a fluid property called ‘viscosity’
 E.g. of real fluids; blood

9. VOLUMETRIC FLOW RATE
 It is the volume of fluid which passes through a given surface per unit time.
 The SI unit is m3·s−1.
 𝑰 𝒗 =
∆𝑽
∆𝒕
 𝑰 𝒗 =
∆𝑽
∆𝒕
=
𝐴. 𝑉. 𝑡
𝑡
= 𝐴. V
 𝑰 𝒗 = A. 𝑉 = constant
 The above equation shows when flow is stationary

10. In our body: A↑, v↓
Conclusion:
 A decrease in the diameter and or length of tube leads to a decrease in velocity of
blood flow
 The more the branches, the less the velocity of blood flow
 The higher the cross-section area, the lower the blood velocity

11. BERNOULLI’S LAW
Bernoulli's principle states that
for an inviscid flow, an increase in
the speed of the fluid occurs
simultaneously with a
decrease in pressure or a decrease
in the fluid’s potential energy
𝒑 + 𝟏
𝟐 𝐩. 𝒗 𝟐 + 𝒑. 𝒈. 𝒉 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕
Static dynamic hydrostatic
Pressure pressure pressure

12. Consequences of Bernoulli’s law:
 It states that an increase in velocity of fluid leads to a decrease in
pressure
 In a tube, the centre which has the lowest pressure experiences the
quickest flow leading to an increase in the number of particles in the
centre. E.g. in blood flow, more cells go with the mainstream
 This is because particles always move to areas of lower energy states/
concentration
 Practical example; when u open the window of a moving car, your
hair tries to fly out of the car

13. Newton’s Law of Friction
𝐹 = 𝜂. 𝐴.
Δ𝑣
Δℎ
η = f ( T; v: in the case
of non-newtonian fluids)
Newton’s law of friction tells us why an increase in
total cross- section still leads to a decrease in
velocity. i.e. resistance increases
1 pascal (Pa) = 1 N/m2

14. Hagen- Poiseuille Law
Hagen–Poiseuille equation is a physical law that gives the pressure drop in a fluid flowing
through a long cylindrical pipe. The assumptions of the equation are that the fluid
is viscous and incompressible; the flow is laminar through a pipe of constant circular cross-
section that is substantially longer than its diameter; and there is no acceleration of fluid in
the pipe.
R- radius 𝜼- viscosity 𝚫p- change in pressure 𝚫𝒍- length

15. CONSEQUENCE OF HAGEN-POISEUILLE LAW