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ESA2 > CVS S5 - Blood Flow > Flashcards

CVS S5 - Blood Flow Flashcards

0
Q

Define flow

A

The volume of fluid passing a given point per unit time

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1
Q

What drives flow?

A

A gradient of pressure

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2
Q

Define velocity

A

Rate of movement of fluid particles along the tube

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3
Q

What is laminar flow?

A

There is a gradient of flow from the middle to the edge of a blood vessel
Velocity is highest at the centre
Fluid is stationary at the edge
Most blood flow is laminar

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4
Q

What is turbulent flow?

A

When layers of fluid try to move over one another faster than physics will allow
As velocity increases, eventually flow will become turbulent
Turbulence greatly increases resistance

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5
Q

Define viscosity

A

The extent to which fluid layers resist flowing over one another

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6
Q

What are the effects of viscosity on flow?

A

The higher the viscosity, the lower the difference between the velocity of flow in the middle and the edge of a vessel
The higher the viscosity, the lower the velocity

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7
Q

What is the effect of tube diameter on velocity?

A

Velocity is proportional to cross sectional area of a tube

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8
Q

How does viscosity affect resistance?

A

The greater the viscosity, the greater the resistance

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9
Q

Describe the relationship between pressure and resistance if flow is fixed

A

If flow is fixed, then the higher the resistance, the greater the pressure change from one end of the vessel to the other.

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10
Q

Describe the relationship between flow and resistance if pressure is fixed

A

If pressure is fixed then the higher the resistance, the lower the flow.

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11
Q

What is the relationship between radius of vessel and resistance?

A

Resistance decreases with the 4th power of the radius

This means small changes in radius can have a great effect on resistance

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12
Q

How is resistance combined for vessels in series?

A

The resistances for each vessel are added

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13
Q

How is resistance combined for vessels in parallel?

A

The resistance for each is reduced as there is another path for the blood to go

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14
Q

Describe flow over the systemic circulation

A

Flow remains the same at all points

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15
Q

Describe resistance and pressure changes in arteries

A

Resistance is low in arteries

There is a low pressure drop from one end of an artery to the other

16
Q

Describe resistance and pressure changes in arterioles

A

Resistance is high

Pressure change from one end of an arteriole to the other is high

17
Q

Describe resistance in veins and venules

A

Resistance is low

Pressure change from one end to the other is low

18
Q

Why are arteries high pressure?

A

Because the arterioles directly after them are high resistance
It’s hard to push blood into them
Therefore pressure increases

19
Q

What is transmural pressure?

A

Stretches vessels

Generated by pressure in distensible vessels

20
Q

Describe blood flow through distensible vessels

A

The higher the pressure in the vessel, the more stretched the vessel so the wider the lumen so more laminar flow so lower the resistance so flow increases
If pressure falls to zero, vessel walls collapse and flow ceases

21
Q

Describe the capacitance property of distensible vessels

A

As vessels widen under increasing pressure, more blood transiently flows in than out
This allows distensible vessels to store blood - conferring capacitance
Veins are the most distensible (67% of their blood is at rest)

22
Q

Describe systolic arterial pressure and what factors affect it

A 
Maximum arterial pressure
Usually ~120 mmHg
Affected by:
-How hard the heart pumps
-Total peripheral resistance (TPR)
-Compliance (stretchiness) of arteries
23
Q

Describe diastolic arterial pressure and what factors affect it

A 
Minimum arterial pressure
Usually ~80mmHg
Affected by:
-Systolic pressure
-TPR
24
Q

What is pulse pressure?

A

The difference between systolic and diastolic pressure

Usually ~40mmHg

25
Q

What is the average arterial pressure?

A

Diastolic pressure plus 1/3rd of systolic pressure

Because systole is shorter than diastole

26
Q

Define TPR

A

Total peripheral resistance

The sum of the resistance of all the peripheral vasculature of the systemic circulation

27
Q

What is the pulse wave?

A

A pulse wave is brought about by contraction of the ventricles
Travels faster than blood
Can be felt at various locations where arteries may be pushed against a reasonably hard surface

28
Q

What is the dicrotic notch?

A

The slight dip in the pulse wave caused by slight back flow as blood flows back through the aortic valve as pressure in the LV goes below that in the aorta

29
Q

What is the dicrotic wave?

A

The slight rise seen in the pulse wave directly after the dicrotic notch
Caused by the recoil of blood as the aortic valve closes

30
Q

Describe the importance of smooth muscle in arteriolar walls

A

Smooth muscle can be contracted or relaxed so can increase or decrease resistance and blood flow to tissues

31
Q

What is vasomotor tone?

A

The degree to which vascular smooth muscle is contracted
If more contracted, vasoconstriction
If less contracted, vasodilation/vasodilatation
In all but maximum flow conditions, muscle is at least partially contracted

32
Q

What determines vasomotor tone?

A

Mainly a sympathetic branch of the ANS
Alpha 1 adrenergic receptors
Antagonised by vasodilator factors, so tone is determined by a balance

33
Q

What are vasodilator metabolites and what do they do?

A

Produced by metabolically active tissues
Eg K, H, adenosine
Cause relaxation of local smooth muscle
So increase flow and decrease resistance

34
Q

What is reactive hyperaemia?

A

If a limb has blood flow cut off for a few minutes then when restored, the local arterioles will have dilated maximally (due to buildup of vasodilator metabolites) so blood flow will be very high

35
Q

What is auto regulation?

A

At most levels of metabolic activity, organs automatically take the amount of blood they require so long as the pressure of the arteries remains within a certain range

36
Q

Define central venous pressure

A

The pressure in the great veins

37
Q

Define venous return

A

The rate of flow of blood back to the heart (limits cardiac output)

ESA2 (39 decks)

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