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Flashcards in Blood Pressure Regulation Deck (66):
1

Factors affecting blood pressure

Total peripheral resistance
Cardiac output
Blood volume
Elasticity

2

What are resistance vessels?

Arterioles

3

What are muscular arterioles?

Resistance vessels

4

What is systolic blood pressure?

Maximum pressure in arteries
When blood is ejected into them during systole

5

What is diastolic pressure?

Minimum pressure in arteries
Blood draining into remaining vessels in diastole

6

Pulse pressure

Difference between systolic and diastolic pressure

7

Mean arterial pressure

Average pressure responsible for driving blood forward through vessels into tissues throughout cardiac cycle

8

How many cm of water does 1mmHg equal?

1.36 cmH2O

9

Different pressures in circulatory system
1)
2)
3)

1) Driving pressure
2) Transmural pressure
3) Hydrostatic pressure

10

Driving pressure

Difference in blood pressure between different parts of the vasculature

EG: Diff between arteries and veins

Vector parallel and in the same direction as blood flow

11

Transmural pressure

Pressure inside vessel vs pressure outside vessel

Runs perpendicular to driving pressure

12

Effect if transmural pressure is negative

No blood flow
Pressure outside vessel is greater than inside

13

Hydrostatic pressure

Difference in pressure form height of blood

Function of potential energy

14

Difference in blood pressure between heart and head

~85mmHg (if head is 50cm higher than heart)

15

Factors contributing to pressure in circulation
1)
2)
3)
4)

1) Gravity
2) Compliance of vessel
3) Viscous resistance
4) Intertia

16

Effect of gravity on blood pressure

Causes hydrostatic pressure when there is a change in height

Doesn't affect driving pressure

Rho G H

17

Vascular compliance

Increase in volume/Increase in pressure

18

Factors determining viscous resistance of blood
1)
2)
3)
4)
5)

1) Fibrinogen concentration
2) Haematocrit
3) Vessel radius
4) Linear velocity
5) Temperature

19

Velocity of blood at vessel wall

Zero

20

Area where blood velocity is maximum

Centre of vessel

21

Effect of increased blood velocity

Decreased pressure

22

Why does blood pressure decrease when velocity increases?

Law of conservation of energy

As kinetic energy (velocity) rises, potential energy (pressure) must decrease

23

Delta P (pressure)

Flow x resistance

24

Issues for Poiseuille's law in the human body

1) Rule is only true for an incompressible liquid
2) Constant velocity
3) Straight, rigid, unbranched tube
4) Steady, not pulsatile flow
5) Uniform flow in a tube

25

What is conductance in a blood vessel?

Measure of blood flow through a vessel for a given pressure difference

26

Ways to calculate conductance

1/Resistance

Flow/Change in pressure

27

What happens to resistance if tubes are in series?

Increases

28

What happens to resistance if tubes are in parallel?

Decreases

29

Is total resistance higher in arterioles or capillaries?

Arterioles

30

Why do arterioles have higher total resistance than capillaries?

Capillaries have a narrower aperture
BUT
Capillaries have more vessels in parallel

31

Role of elasticity in blood pressure

Maintains a steady pressure and flow despite pulsatile heartbeat

32

Does the heart spend more time in systole or diastole?

Diastole

33

Why is vasoconstriction so effective in increasing blood pressure?

Poisuille's equation (radius^4)

60% of blood is in systemic veins --> pushes extra blood into arteries

34

What determines mean arterial pressure?

Cardiac output x total peripheral resistance

35

Equation for MAP

Diastolic pressure + 1/3(Systolic - Diastolic)

36

Preload

What's in the heart before contraction

37

Frank-Starling law

Relationship between stretch and force

Force increases as stretch increases, until a point where it plateaus (sarcomeres stretched too much, heart begins to fail)

38

Cardiac output

Heart rate x stroke volume

39

Average cardiac output

5L/min

40

Stroke volume

End diastolic volume - end systolic volume

41

Average stroke volume at rest

70mL

42

Inotropy

Force of ventricular contaction

43

Factors affecting stroke volume

Inotropy

44

Factors affecting inotropy

Preload
Contractility
Afterload

45

What determines end diastolic volume (afterload)

Venous return
- Skeletal muscle pump, thoracic pump
- Varying degrees of vasoconstriction

46

Increasing afterload increases what?

Resistance
Harder to get blood into the heart
Decrease stroke volume, increase end systolic pressure

47

Effect of increasing preload

Increase stroke volume
Increase end diastolic volume

48

Effect of increasing inotropy

Increase stroke volume
Decrease end systolic volume

49

How is the heartrate modulated?

By autonomic nervous system

50

Effect of sympathetic stimulation on heart
1)
2)
3)
4)
5)

1) Changes ion permeability
2) Depolarises
3) Reaches threshold sooner
4) Beta1 noradrenaline receptors
5) Enhances rate of transmission of AP through AV node

51

Effect of parasympathetic stimulation of the heart
1)
2)
3)
4)
5)

1) Changes ion permeability
2) Hyperpolarises
3) Harder to reach threshold
4) ACh muscarinic receptors
5) Slows conduction of AP through AV node

52

Short term blood pressure regulation

Barroreflex
Neural

53

Where are baroreceptors located?

Carotid sinus
Aortic arch

54

What do baroreceptors in the carotid sinus and aortic arch do?

1) Fire constantly
2) Respond rapidly to changing blood pressure, within 1 - 2 cycles
3) Synapse in medullary cardiovascular control centre

55

Short-term blood pressure homeostais
1)
2)
3)

1) Change in BP detected by baroreceptors in aortic arch, carotid sinus
2) Medullary cardiovascular control centre
3) Either sympathetic or parasympatheitc activation of vasculature

56

Result of activating sympathetic nervous system
1)
2)
3)
4)
5)

1) Increase heart rate
2) Increase contractility
3) Increase total peripheral resistance
4) Increase venous tone
5) Decrease AV conduction time

57

Result of activating parasympathetic nervous system
1)
2)

1) Decrease heart rate
2) Increase AV conduction time

58

Homeostatic mechanisms for blood pressure when you stand up
1)
2)
3)
4)
5)

1) Decrease in MAP
2) Decrease in baroreceptor stretch
3) Decrease in nerve firing to cardiovascular medullary center
4) Increase sympathetic response --> Increase HR, contractility, TPR of arteries
5) Decrease parasympathetic response

59

Homeostatic mechanisms for blood pressure when you lie down

1) Increase in MAP
2) Increase baroreceptor stretch
3) Increase in nerve firing to cardiovascular medullary center
4) Reduce sympathetic response --> decrease TPR of arteries, vascular resistance
5) Increase parasympathetic response --> Decrease heart rate

60

Long-term blood pressure regulation

Chemoreceptors
Detect pH, [O2], [CO2]
Increase respiration

61

Hormonal ways to increase cardiac output

Increase extracellular fluid
Decrease renal salt excretion

62

Hormonal ways to increase TPR

Thicken arterial wall (hypertrophy)
Vasoconstrictive hormones

63

Where are low pressure receptors located?

Atrial baroreceptors

64

Factors determining MAP

1) Blood volume
2) Cardiac output
3) Resistance
4) Distribution of blood between arterial and venous blood vessels

65

What determines resistance to blood flow?

Diameter of arterioles

66

What determines the distribution of blood between arterial and venous systems?

Diameter of veins