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Flashcards in Heart Physiology Deck (42):
1

What is an equation to calculate blood pressure?

Cardiac output x total peripheral resistance

2

What constitutes cardiac output?

Heart rate x stroke volume

3

What is total peripheral resistance?

Resistance to forward flow of blood from the left ventricle

4

What is systolic pressure?

Blood pressure during left ventricular contraction

5

What is diastolic pressure?

Blood pressure during left ventricular relaxation/elastic recoil of large arteries

6

Reason for regulating blood pressure

Maintain steady blood flow to tissues and organs
Avoid ischaemia, necrosis

7

Hagen-Poiseuille equation

Change in pressure = (8 x viscosity x length x flow)/(Pi x radius^4)

8

What is the main implication of Hagen-Poiseuille equation?

A small change in the radius of a blood vessel has a large effect on blood pressure (radius to the power of four)

Injections have a maximum output/unit time

9

Pulse pressure

Systolic - diastolic

10

Mean arterial pressure

Diastolic + 1/3 x pulse pressure

11

Features of the fast control system of blood pressure

Sensors are mainly stretch receptors in the aorta, carotid arteries

Neural linking to brainstem

Effectors are cardiac output, vasomotor tone

12

Features of the slow control system of blood pressure

Sensors in kidneys

Receptors detect stretch in blood vessels, diffusion of electrolytes

Respond with hormones that influence vasomotor tone, fluid/electrolyte balance

13

Sensors of the fast control system

Stretch receptors in the carotid sinus, aortic arch

14

Which nerves connect the carotid sinus, aortic arch stretch receptors to the brain stem?

Cranial nerves IX, X

15

What do cranial nerves IX and X do (related to blood pressure)?

Connect the carotid sinus and aortic arch stretch receptors (baroreceptors) to the brainstem

16

What occurs when the baroreceptors in the carotid sinus and aortic arch detect an increase in blood pressure?

Send more impulses to the inhibitory centres of the brainstem

17

Where is the vasomotor area located?

In the brainstem

18

Inputs to the vasomotor area
1)
2)
3)
4)

1) Baroreceptors
2) Chemoreceptors
3) Skeletal muscle proprioceptors
4) Hypothalamus (body temperature)

19

Afferents from the vasomotor area

Vagus nerve
Sympathetic nervous system

20

What does the vagus nerve afferent do?

Leads to the cardiac inhibitory function

Removed if higher heart rate is required

21

What is the effect of sepsis on blood pressure?

Decreases blood pressure (systemic vasodilation)

22

Effects of sympathetic activity on blood pressure
1)
2)
3)
4)

1) Increase heart rate, stroke volume
2) capacitance vessels - veins - change diameter
3) Resistance vessels - arterioles - change diameter
4) Adrenal gland secretes adrenaline

23

Effectors of blood pressure
1)
2)
3)
4)

1) Heart
2) Veins (capacitance vessels)
3) Arterioles (resistance vessels)
4) Adrenal gland

24

What does vasoconstriction of capacitance vessels do?

Emptying of blood in reservoirs into circulation
EG: Splanchnic bed

25

Example of abnormal CNS control of blood pressure

Harlequin syndrome

26

What is Harlequin syndrome?

Asymmetrical flushing and sweating of thorax, neck, face

27

How does the kidney respond to a decrease in blood pressure?

Secretes renin

28

What does the kidney detect, apropos of blood pressure?

Stretch receptors, electrolyte balance

29

What does angiotensin do?

Vasoconstriction

Secretion of aldosterone

30

What is renin converted to?

Vasopressin

31

What does aldosterone do?

Retain sodium and water in kidney.

Increases blood pressure

32

Potential dangers of faliure of fluid regulation: overload

Pulmonary oedema

Wound dehiscence

33

Local effects of exercise
1)
2)
3)
4)
5)

1) Blood flow to skeletal muscle increases 30x
2) Potassium, CO2, temperature rise, O2 fall
3) Temperature rise leads to vasodilation
4) Number of open capillaries increases 10-100-fold
5) up to 100-fold increase in O2 consumption

34

Systemic effets of exercise
1)
2)
3)

1) Arterial dilation
2) Vasodilation
3) Adrenaline secretion

35

Change in percentage of blood flow received by muscles at rest and during exercise

13% to 88%

36

Change in percentage of blood flow received by kidneys at rest and during exercise

19% to 1%

37

Change in percentage of blood flow received by stomach at rest and during exercise

21% to 1%

38

Change in percentage of blood flow received by brain at rest and during exercise

13% to 3%

39

Orthostatic hypertension
1)
2)
3)
4)
5)
6)
7)

1) Move from a lying to a standing position
2) Decrease in arterial pressure
3) Detected by baroreceptors (carotid, aortic)
4) Decrease in firing from arterial baroreceptors
5) Reflex via the medullary cardiovascular centre
6) Increase sympathetic/decrease parasympathetic signals to the heart
7) Increase heart rate, stroke volume, arteries and veins contract

40

When are chemoreceptors in the aorta stimulated?

Only when the heart is severely lacking in blood supply

41

How is blood redirected to different organs?

Constriction and dilation of arterioles

42

Response to significant blood loss

1) Reduced stretch in baroreceptors
2) Inhibition of vagal cardiac inhibition
3) Increase in heart rate, stroke volume
4) Sympathetic constriction of arterioles in skin, veins in splanchnic circulation
5) Juxtoglomerular apparatus in kidney stimulated by decrease in blood pressure, filtering in kidneys --> kidneys release renin
6) renin-angiotensin, aldosterone lead to increased fluid retention