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My LSS- CVS > CVS 4: Bloodflow > Flashcards

CVS 4: Bloodflow Flashcards

1
Q

Describe the structure and function of the large arteries

A

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

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2
Q

Describe the structure and function of smaller arteries

A

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

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3
Q

Describe the structure and function of veins

A

Very stretchy and highly compliant

Act as a reservoir for blood volume

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4
Q

Describe the structure and function of capillaries

A

Very thin walls

Facilitates transport and diffusion of nutrients

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5
Q

What is Darcy’s Law?

A 
Flow in a fluid circuit:
DP= Q x R
DP= change in pressure
Q= volumetric flow
R= Resistance
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6
Q

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

A

MBP= CO x PVR

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7
Q

What assumptions are made about the Peripheral Vascular Resistance?

A

This is an approximation because:

  1. It assumes a steady flow (which doesn’t occur because of the intermittent pumping of the heart)
  2. That the vessels are rigid
  3. That right atrial pressure is negligible (on L.atrial pressure creating the force)
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8
Q

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

A

Viscous (frictional) pressure losses

Small arteries and arterioles

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9
Q

Which three variables affects the resistance to blood flow?

A
  1. Fluid viscosity (mostly constant)
  2. Length of tube (remains constant)
  3. Inner radius of tube (main determinant)
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10
Q

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

A

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

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11
Q

What happens in terms of vasoconstriction and dilation during exercise?

A

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

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12
Q

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

A

LAMINAR FLOW

  • streamlined flow
  • doesn’t interfere with each other
  • velocity of the fluid is constant at any one point
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13
Q

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

A 
TURBULENT FLOW
- Irregular flow 
- Tiny whirlpool regions 
- velocity not constant at any one point
Could be PATHOPHYSIOLOGICAL
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14
Q

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

A

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

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15
Q

Where in the vessel does blood flow quickest and why?

A
  • Velocity increases as distance from wall increases (middle flows faster than sides)
  • Because of adhesive forces which attach the blood to the vessel walls
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16
Q

What is shear rate?

A

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

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17
Q

What is shear stress?

A

Shear rate x viscosity

18
Q

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

A

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

19
Q

What happens when shear stress is high?

A
  • Promotes endothelial cell survival
  • Endothelial cells line up in direction of flow
  • Endothelium produces substances (which promote vasodilation and anticoagulation) normally
20
Q

What happens when shear stress is low?

A
  • Happens during turbulent flow
  • Endothelial proliferation is stimulated
  • Apoptosis
  • Shape change
  • secretion of substances which promote vasoconstriction, coagulation and platelet aggregation
21
Q

How do you measure blood pressure?

A
  1. Put cuff around arm and increase pressure until it exceeds arterial pressure
  2. Place stethoscope distal to cuff- you won’t hear anything because the blood flow is occluded
  3. Slowly reduce the pressure of the cuff
  4. When pressure in cuff will just become overcome by arterial pressure
  5. Blood will start to squirt through and set up turbulent flow and you will hear a light tapping sound
  6. Continued reduction of cuff pressure => laminar flow again = no sound
22
Q

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

A 
APPEARANCE= systolic blood pressure
DISAPPEARANCE= diastolic blood pressure
23
Q

What is pulse pressure?

A

Difference between systolic and diastolic blood pressure

24
Q

What is mean blood pressure?

A

Diastolic bp + 1/3 of PP

25
Q

Why does aortic pressure fall more slowly than ventricular pressure?

A

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

26
Q

What causes the dichrotic notch?

A

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

27
Q

What is the dampening effect of the aorta also called?

A

The Windkessel effect

28
Q

What happens to blood flow with age?

A
  • Arterial compliance decreases
  • The dampening effect reduces
  • The PP increases
29
Q

What is the Laplace’s relationship?

A

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

30
Q

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

A 
circumferential stress (sigma)= tension force (T)/ wall thickness (h)
Vessel wall distension
31
Q

What is compliance? and what is it dependent on?

A
  • The relationship between transmural pressure and vessel volume
  • Vessel Elasticity
32
Q

What is an aneurysm?

A
  • Occurs over a prolonged period
  • Vessel walls weaken causing a balloon like distension
  • A result of Laplace’s Law–> increase in radius
33
Q

What causes aneurysms to expand and rupture?

A
  • 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
34
Q

What other pathophysiological effect does Laplace’s law cause?

A

Diverticuli in the gut

35
Q

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

A
  • 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
36
Q

What happens in the veins during smooth muscle contraction?

A

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

37
Q

What is postural hypotension?

A
  • 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)
38
Q

What happens to overcome postural hypotension?

A
  • 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
39
Q

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

A

Syncope (fainting)

Hypovolaemia- may become thirst and blood volume decreases

40
Q

What is the skeletal pump?

A
  • Contraction of muscle squeezes blood back through veins into the heart
  • Decreases venous capacitance
41
Q

What is the respiratory pump?

A

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

42
Q

Name two problems with standing

A
  • Varicose veins because of incompetent valves

- oedema in your feet because of elevated venous pressure

My LSS- CVS (21 decks)

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