CVS 4: Bloodflow Flashcards by Meghna Irukulla

Describe the structure and function of the large arteries

Large, thick-walled and elastic which dampen the high pressure of blood from the heart

How well did you know this?

Not at all

Perfectly

Describe the structure and function of smaller arteries

Have extensive smooth muscle in their walls to REGULATE their diameters and provide RESISTANCE to blood flow

How well did you know this?

Not at all

Perfectly

Describe the structure and function of veins

Very stretchy and highly compliant

Act as a reservoir for blood volume

How well did you know this?

Not at all

Perfectly

Describe the structure and function of capillaries

Very thin walls

Facilitates transport and diffusion of nutrients

How well did you know this?

Not at all

Perfectly

What is Darcy’s Law?

Flow in a fluid circuit:
DP= Q x R
DP= change in pressure
Q= volumetric flow
R= Resistance

How well did you know this?

Not at all

Perfectly

How can you relate Darcy’s law to the body’s circulation?

MBP= CO x PVR

How well did you know this?

Not at all

Perfectly

What assumptions are made about the Peripheral Vascular Resistance?

This is an approximation because:

It assumes a steady flow (which doesn’t occur because of the intermittent pumping of the heart)
That the vessels are rigid
That right atrial pressure is negligible (on L.atrial pressure creating the force)

How well did you know this?

Not at all

Perfectly

What causes pressure to fall across the circuit? And where is the most pressure lost?

Viscous (frictional) pressure losses

Small arteries and arterioles

How well did you know this?

Not at all

Perfectly

Which three variables affects the resistance to blood flow?

Fluid viscosity (mostly constant)
Length of tube (remains constant)
Inner radius of tube (main determinant)

How well did you know this?

Not at all

Perfectly

Which law states the importance of artery radius for altering resistance?
*Can you remember the equation?

Poiseuille’s Equation
R= 8Ln/πr^4
= small increase in radius=> massive decrease in resistance because of the power

How well did you know this?

Not at all

Perfectly

What happens in terms of vasoconstriction and dilation during exercise?

Vasoconstriction of blood to some organs (to the intestines, kidneys etc.)
Vasodilation of blood to skeletal muscle, liver)

How well did you know this?

Not at all

Perfectly

What sort of blood flow do you get in vessels? Describe this type of flow

LAMINAR FLOW

streamlined flow
doesn’t interfere with each other
velocity of the fluid is constant at any one point

How well did you know this?

Not at all

Perfectly

What is the opposite of laminar flow? Describe the characteristics of this type of flow

TURBULENT FLOW
- Irregular flow 
- Tiny whirlpool regions 
- velocity not constant at any one point
Could be PATHOPHYSIOLOGICAL

How well did you know this?

Not at all

Perfectly

Which type of flow produces sound and what are these sounds called?

TURBULENT FLOW produces sounds and these sounds are called the sounds of korotkoff

How well did you know this?

Not at all

Perfectly

Where in the vessel does blood flow quickest and why?

Velocity increases as distance from wall increases (middle flows faster than sides)
Because of adhesive forces which attach the blood to the vessel walls

How well did you know this?

Not at all

Perfectly

What is shear rate?

The velocity gradient in the vessel= difference between highest velocity in the middle of the lumen and the lowest velocity by the sides

How well did you know this?

Not at all

Perfectly

What is shear stress?

Shear rate x viscosity

What is caused by shear stress? What is the importance of this?

Pathophysiological changes to endothelial function.
Important for:
- Laminar flow
- production of transmitter substances involved in vessel dilation and constriction

What happens when shear stress is high?

Promotes endothelial cell survival
Endothelial cells line up in direction of flow
Endothelium produces substances (which promote vasodilation and anticoagulation) normally

What happens when shear stress is low?

Happens during turbulent flow
Endothelial proliferation is stimulated
Apoptosis
Shape change
secretion of substances which promote vasoconstriction, coagulation and platelet aggregation

How do you measure blood pressure?

Put cuff around arm and increase pressure until it exceeds arterial pressure
Place stethoscope distal to cuff- you won’t hear anything because the blood flow is occluded
Slowly reduce the pressure of the cuff
When pressure in cuff will just become overcome by arterial pressure
Blood will start to squirt through and set up turbulent flow and you will hear a light tapping sound
Continued reduction of cuff pressure => laminar flow again = no sound

What can you determine from the appearance and disappearance of sound?

APPEARANCE= systolic blood pressure
DISAPPEARANCE= diastolic blood pressure

What is pulse pressure?

Difference between systolic and diastolic blood pressure

What is mean blood pressure?

Diastolic bp + 1/3 of PP

Why does aortic pressure fall more slowly than ventricular pressure?

Elasticity of the aorta buffers the changes in pressure and maintains the pressure

What causes the dichrotic notch?

When blood enters the aorta faster than it leaves the aorta =>About 40% of the stroke volume is stored by the elastic arteries.

What is the dampening effect of the aorta also called?

The Windkessel effect

What happens to blood flow with age?

- Arterial compliance decreases - The dampening effect reduces - The PP increases

What is the Laplace's relationship?

It describes the tension force (T) in the wall created by transmural pressure. T= P x r The larger the vessel radius, the greater the wall tension required to withstand a given internal fluid pressure

What is the equation for circumferential stress? and what is the consequence of maintained high circumferential stress?

``` circumferential stress (sigma)= tension force (T)/ wall thickness (h) Vessel wall distension ```

What is compliance? and what is it dependent on?

- The relationship between transmural pressure and vessel volume - Vessel Elasticity

What is an aneurysm?

- Occurs over a prolonged period - Vessel walls weaken causing a balloon like distension - A result of Laplace's Law--> increase in radius

What causes aneurysms to expand and rupture?

- For the same internal pressure, the inward force exerted by the muscle wall must increase. - If the muscle fibre is weakened and the compliance isn't great, force needed to withstand pressure isn't produced => aneurysm continues to expand

What other pathophysiological effect does Laplace's law cause?

Diverticuli in the gut

Which vessel has the highest compliance and what does this mean?

- Venous compliance is greater than arterial compliance at low pressures - small changes in venous pressure distends veins and increases the volume of blood stored in them => for the same pressure, veins can hold a much larger volume of blood

What happens in the veins during smooth muscle contraction?

Smooth muscle contraction => decreases venous volume => increases venous pressure So you can change the volume of blood in the reservoir

What is postural hypotension?

- Pooling of blood in the lower limbs because of venous volume/ capacitance - Reduces venous return to he heart - Cardiac Output and Blood pressure falls ( less blood goes to the brain as a result of this)

What happens to overcome postural hypotension?

- SYMPATHETIC nervous system activates - Venous smooth muscle constricts and stiffens veins - Constricts arteries to increase TPR and maintain BP - increase in HR and force of contraction to maintain CO

What happens if there is a failure of mechanisms to control postural hypotension?

Syncope (fainting) | Hypovolaemia- may become thirst and blood volume decreases

What is the skeletal pump?

- Contraction of muscle squeezes blood back through veins into the heart - Decreases venous capacitance

What is the respiratory pump?

Breathing in, chest expands, intrathoracic pressure decreases which allow blood to come back into the right atrium and increase venous return

Name two problems with standing

- Varicose veins because of incompetent valves | - oedema in your feet because of elevated venous pressure