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Year 1: Cardiovascular System > 4. Blood Vessels and Blood Flow > Flashcards

4. Blood Vessels and Blood Flow Flashcards

1
Q

What are the features of arteries?

A

Large, thick-walled and elastic

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2
Q

What are the features of small arteries and arterioles?

A

Extensive smooth muscle, used to produce resistance to blood flow

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3
Q

Where does most of the pressure drop in the arteries occur?

A

Small arteries and arterioles

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4
Q

What are the features of veins?

A

Very stretchy and highly complient

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5
Q

What is the main function of veins?

A

Reservoir for blood volume

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6
Q

Which blood vessel makes up the largest cross sectional area in the CVS?

A

Capillaries - has exchange function

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7
Q

What happens to the store of blood during exercise?

A

Vasoconstriction, the store of blood decreases and more blood moves back to the heart.

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8
Q

What effects does a decreased volume of stored blood have?

A

Increased venous return so more cardiac output

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9
Q

Mean Arterial Blood Pressure =

A

Cardiac output x Resistance

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10
Q

What can the pressure difference be estimated as?

A

Mean arterial blood pressure

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11
Q

Define resistance?

A

The resistance of all the vessels, also called peripheral vascular resistance

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12
Q

What is the equation for the mean blood pressure?

A

Delta P = QR

MBP = Cardiac output (CO) x Resistance (PVR)

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13
Q

How is the regulation of flow achieved?

A

Variation in resistance while the blood pressure remains relatively constant

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14
Q

Why does pressure fall across the circulation?

A

This is due to viscous (frictional) pressure losses

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15
Q

What vessels present the most resistance to flow?

A

small arteries and arterioles

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16
Q

What three variables affect the resistance to blood flow?

A

Fluid viscosity
Length of tube
Inner radius of tube

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17
Q

What is the main variable that affects the resistance to blood flow?

A

Inner radius of tube

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18
Q

How does halving the radius affect blood flow?

A

It would decrease blood flow 16 times.

R=1/r^4

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19
Q

When exercising what can we boost our cardiac output to?

A

25L/min

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20
Q

How can we increase the blood flow to working skeletal muscle

A

Vasoconstriction and vasodilation

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21
Q

What is laminar flow?

A

Blood flowing in stream lines

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22
Q

What is turbulent flow?

A

Blood flowing in whirlpool like flow. Sounds of korotkoff when using a pressure cuff and stethoscope

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23
Q

Describe the speed of blood flowing in a blood vessel

A

Blood flows quickest in the middle and slowest on the sides

24
Q

Why is there varying speed of blood flow within a blood vessel?

A

This is due to adhesive forces which attach blood to the vessel walls. Velocity increases as distance from the wall increases

25
Q

Define shear rate

A

The velocity gradient that is established - the difference between the highest velocity blood in the middle of the lumen and the lowest velocity blood that adheres to the blood vessel walls

26
Q

What is the equation for shear stree?

A

Shear stress = Shear rate x Viscosity

27
Q

What happens when there is high shear stress?

A

Promotion of endothelial survival. They line up and produce substances normally - found in laminar flow

28
Q

What happens when there is low, disturbed or changed shear stress?

A

Endothelial proliferation affecting vasoconstriction, coagulation, platelet aggregation and atheroma formation - found in turbulent flow

29
Q

What is high shear stress the same as?

A

Normal shear stress

30
Q

Measuring Blood Pressure - sound appears?

A

Systolic blood pressure

31
Q

Measuring Blood Pressure - sound disappears?

A

Diastolic blood pressure

32
Q

What is pulse pressure?

A

Systolic BP - Diastolic BP

33
Q

Mean blood pressure =

A

Diastolic BP + 1/3 of Pulse pressure

34
Q

Describe the pressure changes in the aorta and ventricles once the aortic valve closes

A

The ventricular pressure falls rapidly but the aortic pressure only falls slowly

35
Q

Why do these pressure changed occur in the aorta and ventricles once the aortic valve closes?

A

The aorta is elastic so it buffers pressure changes preventing the pressure to dropping to zero

36
Q

Define dichrotic notch

A

This is a secondary upstroke in aortic pressure after blood has left the heart. When blood enters the aorta faster than it leaves the aorta, about 40% of the stroke volume is stored by the elastic arteries. There is a recoil from the elastic aorta and arteries producing the dichrotic notch

37
Q

What is the name of the dampening effect on blood pressure?

A

Windkessel effect

38
Q

What happens to the pulse pressure with increasing age?

A

The arterial compliance decreases with age decreasing the dampening effect of windkessel, increasing pulse pressure

39
Q

What is the name of the pressure inside the vessel?

A

Transmural pressure

40
Q

What is the effect of pressure inside the vessel?

A

It causes distension of the vessel wall

41
Q

What is Laplace’s Law?

A

T = P x r

42
Q

What does circumferential stress depend on?

A

Vessel wall thickness

CS = (P x r)/h h = wall thickness

43
Q

What describes compliance?

A

The relationship between the transmural pressure and vessel volume

44
Q

What is compliance depended on?

A

Vessel elasticity

45
Q

Summarise Laplace’s law

A

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

46
Q

What is the venous compliance compared to arterial compliance?

A

10 to 20 times greater

47
Q

What is the cause of postural hypotension?

A

When you stand up quickly, gravity makes the blood pool in the legs which is due to the venous volume/capacitance
When it pools in the legs, this reduces venous return to the heart which means that cardiac output falls and you get less blood going to the brain
A mechanism to compensate for the postural hypotension is that you get venous constriction which means that more blood is returned to the heart and cardiac output is increased

48
Q

What does standing cause the activation of?

A

Sympathetic nervous system

49
Q

In terms of standing, what does the sympathetic nervous system do?

A

Stiffens and constricts veins

50
Q

What happens when you stand?

A

1) Arteries constrict to increase total peripheral resistance and maintain blood pressure
2) Slight increase in heart rate and increase in force contraction - increases blood to brain
3) Veins stiffen and constrict

51
Q

What happens when the compensatory mechanisms for standing fail?

A

1) Fainting - syncope

2) Hypovolaemia - you may become thirsty and your blood volume may drop

52
Q

What types of circulatory pumps exist?

A

Skeletal muscle pump

Respiratory pump

53
Q

How does the skeletal pump work?

A

Through the contraction of the muscle it squeezes blood back through the veins to the heart

54
Q

What is the point of the skeletal pump?

A

It assist the movement of blood back to the heart ad decreases venous capacitance

55
Q

How does the respiratory pump work?

A

As we breathe in, we expand our chest so our intrathoracic pressure decreases. This allows blood to come back into the right atrium and increase venous return

56
Q

What causes varicose veins?

A

Incompetent valves

57
Q

What occurs with prolonged elevation of venous pressure?

A

Oedema in your feet

Year 1: Cardiovascular System (21 decks)

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