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Cardiovascular System > Bloodflow > Flashcards

Bloodflow Flashcards

1
Q

What are the different vessels in the body?

A
  • Arteries
  • Smaller arteries and arterioles
  • Veins
  • Capillaries
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2
Q

What is the importance of each type of vessel in the circulatory system?

A
  • Large arteries – dampening effect
  • Smaller arteries and arterioles - main pressure decrease occurs here
  • Veins and venules act as a reservoir
  • Capillaries - exchange
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3
Q

What is venoconstriction and what does it lead to?

A
  • Decrease the amount of stored blood and move more blood back to the heart e.g. during exercise
  • Leads to larger CO and more venous return
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4
Q

Is the relative volume of the vessels equivalent to the relative cross- sectional area?

A

NO

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5
Q

How is blood flow regulated?

A

Variation in resistance while blood pressure remains relatively constant

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6
Q

How can blood flow be directed to an area?

A

By contraction and relaxation of the blood vessels that go to an area

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7
Q

How does pressure change as you go along the circulatory system and why?

A
  • Decreases as you go along

* Pressure falls due to friction

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8
Q

Which vessels provide a resistance to blood flow?

A
  • Small arteries and arterioles (most)

* Pulmonary artery

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9
Q

Which factors affect resistance of a blood vessel?

A
  • Fluid Viscosity - not fixed but in most physiological conditions this remains constant
  • Length of Tube - fixed
  • Inner Radius of Tube - variable - main determinant of resistance
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10
Q

What is the equation that shows the importance of artery diameter to resistance?

A

Poisuille’s equation emphasises the importance of artery diameter to alter resistance

R= 8Ln/pi*r^4

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11
Q

How would halving the radius affect blood flow?

A
  • It would decrease blood flow 16 times

* The power function means that a relatively small change in radius produces a large change in blood flow

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12
Q

During exercise what can cardiac output be maximised to?

A

25 L/min

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13
Q

How can blood flow to skeletal muscles be increased during exercise?

A

By changing the radius of various - constricting and dilating others to direct the blood to the place that needs it most

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14
Q

What sort of blood flow occurs in vessels?

A

laminar flow

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15
Q

What is laminar flow and what are its features?

A
  • Stream lines which don’t tend to interfere with one another
  • You can’t hear laminar flow
  • Velocity of blood flow at a given point are equal
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16
Q

How is laminar flow utilised to measure blood pressure?

A
  • You pump the cuff up to obstruct blood flow and when you start to release the cuff slowly, the blood will start pushing through the cuff producing turbulent flow which you can hear (sounds of korotkoff)
  • You hear a soft tapping sound
  • When you further drop the pressure in the blood pressure cuff, you won’t hear anything at all because the vessel is no longer occluded, and the blood starts to flow in a laminar fashion
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17
Q

What does the appearance of the sound during blood pressure measure give you the value of?

A

Systolic Blood Pressure

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18
Q

What does the disappearance of the sound during blood pressure measure give you the value of?

A

Diastolic Blood Pressure

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19
Q

What does the difference between systolic and diastolic blood pressure give?

A

Pulse pressure (force generated by heart during contraction)

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20
Q

How is mean blood pressure calculated using diastolic and pulse pressure?

A

Diastolic + 1/3 of pulse pressure

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21
Q

What is turbulent blood flow?

A
  • Whirlpool like regions and the velocity of the fluid is not constant
  • Turbulent flow could bring about pathophysiological changes
  • It can change the shear stress on the vessels
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22
Q

Why does blood flow quickest in the middle and slowest on the sides and what is the effect of this?

A
  • Adhesive forces which attach the blood to the vessel walls

* Velocity increases as distance from wall increases

23
Q

What is shear rate?

A

The rate of change of velocity in the vessel - the velocity gradient at any one point
S= dv/dr

24
Q

What is shear stress and how is it calculated?

A

• Shear rate multiplied by viscosity
T = dv/dr *n

• Shear stress disturbs endothelial function which is important for laminar flow

25
Q

What is the effect of high shear stress?

A
  • Promotes endothelial cell survival (and rest) so the endothelial cells line up and produce substances normally
  • Promotes the secretion of substances that promote vasodilation and anticoagulation
26
Q

What is the effect of low, disturbed or changed (caused by turbulent flow) shear stress?

A
  • Endothelial proliferation and apoptosis is stimulated
  • Stimulates production of substances that promote vasoconstriction, coagulation and platelet aggregation
  • This affects atheroma formation
  • In low shear stress the endothelial cells are all mixed up and don’t behave in a normal way and don’t produce their substances normally
27
Q

Why is shear stress important?

A

It determines how happy the endothelial cells are and determines their function

28
Q

How does normal shear stress affect endothelial cells?

A

Endothelial cells align themselves normally and produce substances normally

29
Q

Why do ventricular and aortic pressure differ?

A
  • Aortic valve closing causes ventricular pressure to fall rapidly but aortic pressure only falls slowly in diastole
  • This is explained by the elasticity of the aorta which buffers changes in pressure and so it doesn’t drop to zero like the ventricular pressure - the pressure is maintained by the elasticity of the vessel
30
Q

What is a dichrotic notch?

A
  • Blood enters the aorta faster than it leaves the aorta (40% of the stroke volume is stored by the elastic arteries)
  • When the aortic valve closes, the ejection of blood stops but there is a recoil because the arteries and the aorta are very elastic which produces the dichrotic notch (small increase in pressure)
  • Allows it to act as a buffer – effect is called the WINDKESSEL effect (so blood isn’t squirted out discontinuously like a pump but a continuous flow)
31
Q

With age arterial compliance decrease, what is the effect of this on the Windkessel effect?

A
  • Effect is reduced

* Pulse pressure increases

32
Q

Which pressure determines the distension of the vessel wall?

A

Transmural pressure - pressure inside vessel

33
Q

What is Laplace’s law of the heart?

A

The larger the vessel radius, the greater the wall tension required to withstand a given internal fluid pressure

34
Q

Define compliance

A
  • Ability of a vessel to expand and increase volume

* Ability of a vessel to resist recoil when a force is applied

35
Q

Compare compliance in arteries and veins

A
  • Venous compliance is 10-20 times greater than arterial compliance at low pressure
  • Relatively 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

Define capacitance

A

The ability of a vessel to increase the blood within it without a large increase in blood pressure.

37
Q

How can the volume of blood in the reservoir be altered?

A

Change the nervous supply to the smooth muscle causing contraction. This will decrease the venous volume and increase venous pressure

38
Q

What causes postural hypotension?

A
  • Blood pools in legs – due to venous volume/capacitance
  • Leads to reduced venous return so CO decreases
  • Venous constriction increases venous return and so CO
39
Q

Why don’t we faint upon standing?

A
  • Standing causes activation of the sympathetic nervous system
  • Leads to constriction of veins
  • The arteries are constricted to increase total peripheral resistance and maintain blood pressure
  • Slight increase in heart rate and an increase in the force of contraction which allows more blood to return to the brain
  • Failure of these mechanisms can lead to fainting (syncope)
  • The failure of the mechanisms could lead to hypovolaemia - you may become thirsty and your blood volume may drop a bi
40
Q

Why is the pressure gradient from artery to capillary maintained?

A

Ensure blood flows in the correct direction

41
Q

Which vessel does gravity have the greatest effect on?

A

Distensible veins in the leg

42
Q

What is the role of the skeletal pump?

A
  • the contraction of the muscle squeezes blood back through the veins to the heart
  • assists the movement of blood back to the heart and decreases venous capacitance
43
Q

What is the role of the respiratory pump?

A
  • Breathing in leads to thorax expansion and a decrease in intrathoracic pressure decreases
  • This allows blood to come back to the right atrium and increase venous return
44
Q

What is the overall benefit of having a skeletal and respiratory pump?

A

Ability to stand without fainting

45
Q

What causes varicose veins?

A
  • Incompetent valves - backflow

* Common in older people

46
Q

What other effect can standing for a long time cause?

A

oedema in feet

47
Q

Why do aneurysm’s form?

A
  • Due to Laplace’s law
  • If an aneurysm forms in the blood vessel, this means that for the same internal pressure, the inward force exerted by the muscular wall must also increase
  • However, if the muscle fibre is weakened and the compliance isn’t great, the force needed to withstand the internal pressure cannot be produced and so the aneurysm will continue to expand
48
Q

Compare the flow of blood in the body to current in a circuit

A

V=IR
delta P= QR
(Q=volumetric flow, P= pressure, R=resistance)

  • Pressure Difference can be estimated as being mean arterial blood pressure
  • Q is the cardiac output
  • Resistance = the resistance of all the vessels - peripheral vascular resistance - this is an approximation because it assumes a steady flow and assumed that the vessels are rigid and that right atrial pressure is negligible
49
Q

What is the relationship between transmural pressure and wall tension?

A
  • explained by Laplace’s law
    T=PR

T - wall stress
P = transmural pressure

50
Q

What does compliance depend on?

A

vessel elasticity

51
Q

What is the relationship between transmural pressure and vessel volume?

A

compliance

52
Q

What is circumferential stress?

  • depends on?
  • equation
A

Cirumferential stress= (P*r)/h

wall thickness (h)

53
Q

What does maintained high circumferential stress cause?

A

Maintained high circumferential stress causes aneurysms (distension) - pressure forcing the vessel out

Cardiovascular System (19 decks)

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