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2. Cardiovascular System > 13. Short Term Control of BP > Flashcards

13. Short Term Control of BP Flashcards

1
Q

What is the equation for calculating MAP?

A

MAP= CO x TPR

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2
Q

What can low MAP cause?

A

fainting (syncope_

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3
Q

What can high MAP cause?

A

hypertension; overtime damages capillary beds leading to cardiovascular disease, stroke etc

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4
Q

Where are baroreceptors found? (2)

A
  1. at the carotid sinus (at internal carotid arteries)

2. at the aortic arch

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5
Q

What effect does pressure in arteries have on vessel stretchability?

A

Makes arteries more stretchable when high pressure is detected during bigger APs

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6
Q

What is resting arterial pressure?

A

-90mmHg

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7
Q

Where do baroreceptors send their impulses to?

A

to the medulla of the brain (cardiovascular centre) which compares the blood pressure

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8
Q

What are baroreceptors?

A
  • stretch receptors

- fire more APs if detect high pressure and stretch artery walls

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9
Q

What is the carotid sinus?

A

area where internal and external carotid arteries split (bifurcate)

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10
Q

What is the AP firing rate throughout the cardiac cycle?

A

Most APs fired at systole and least APs fired during diastole

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11
Q

What nerve sends signals from the carotid sinus baroreceptors to the medulla?

A

glassopharyngeal nerve

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12
Q

What nerve sends signals from the aortic arch baroreceptors to the medulla?

A

vagus nerve

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13
Q

What 2 nerves travel AWAY from the medulla towards the heart?

A
  1. sympathetic nerves

2. parasympathetic (vagus) nerves

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14
Q

What do sympathetic and parasympathetic nerves from the medulla innervate in the heart?

A

the SA node

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15
Q

What receptors do sympathetic nerves act on?

A

alpha 1 receptors

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16
Q

What is the effect of the sympathetic nerves on the heart?

A
  • cause blood vessel constriction
  • cardiac output and stroke volume will increase
  • increase in TPR
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17
Q

What are other inputs to the medullary cardiovascular centres? (5)

A
  1. cardiopulmonary baroreceptors
  2. central chemoreceptors
  3. chemoreceptors in muscle
  4. joint receptors
  5. higher centres
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18
Q

What is another name for cardiopulmonary baroreceptors?

A

low pressure baroreceptors

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19
Q

What happens to baroreceptors firing rate during hypertension and hypotension?

A

Hypertension; increase

Hypotension; decrease

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20
Q

What does decreased sympathetic tone do to lower heart rate? (4)

i.e. increased vagal tone

A
  • reduces veno/arteriolar constriction
  • reduce adrenaline production in adrenal medulla
  • reduce contractility
  • reduce heart rate
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21
Q

What does decreased vagal tone do to increase heart rate? (4)

i.e. increased sympathetic tone

A
  • increases veno and arterial constriction ( increases venomotor tone)
  • increases adrenaline production in adrenal medulla
  • increases contractility
  • increases heart rate
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22
Q

How do signals travel from the medullary CV centres to the veins/arteries smooth muscle?

A

sympathetic nerves

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23
Q

What carries signals from the medullary CV centres to the adrenal medulla?

A

sympathetic nerves

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24
Q

From which spinal level do sympathetic nerves supplying the heart arise from?

A

T5-8

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25
Q

What do chemoreceptors respond to?

A
  • respond to Co2 changes which cause pH changes in the CSF
  • CSF is closely related to blood
  • induces heart to pump more O2 around body in hypoxic situations
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26
Q

When are joint receptors activated?

A

activated during physical activity (during repeated movement)

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27
Q

How does activating central chemoreceptors affect MAP?

A

Activated when high CO2; means increased heart rate and contractility and therefore increased cardiac output and MAP

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28
Q

When do chemoreceptors specifically activate?

A

during exercise

29
Q

What group of receptors are classified as “feedback receptors”?

A
  1. cardiopulmonary baroreceptors ( low pressure baroreceptors)
  2. central chemoreceptors
  3. chemoreceptors in muscle
30
Q

How do higher centres (hypothalamus and cortex) affect MAP before exercise?

A
  • act as feed-forward systems
  • tells CV system that something is about to happen and pre-prepares it to increase the CO
  • gets CV system working before stimulus occurs to be prepared for increase in heart rate in anticipation for blood to muscles
31
Q

Can arterial baroreceptors control and regulate BP in the long run?

A

No, they can’t

32
Q

What does regulation of BP in the long run revolve around?

A

revolves around blood volume

33
Q

What are the main sensors which regulate BP in the long run?

A

cardio-pulmonary baroreceptors

34
Q

In cardiopulmonary baroreceptors, what do their effect tend to be produced as?

A

hormonal effect

35
Q

What structures does hormonal effect mainly influence? (2)

A
  1. blood vessels

2. kidneys

36
Q

Why is arterial baroreceptor reflex important when standing up?

A

Prevents body from fainting when all the blood rushes to the feet

37
Q

How does standing affect MAP?

A

Lower venous return as blood pools in legs causing venous distension.

  • lower EDV
  • lower preload
  • lower SV
  • lower CO
  • lower MAP
38
Q

Define valsalva manoeuvre.

A

Forced expiration against a closed glottis

39
Q

What does valsalva mamoeuvre cause first in the thorax?

A

increase in thoracic pressure

40
Q

How does increased thoracic pressure affect aortic pressure?

A

It’s transmitted through the aorta where it’s added to aortic pressure; therefore MAP rises

41
Q

How does increased thoracic pressure affect venous return?

A

Increased thoracic pressure reduces venous return because it squashes the veins near the heart preventing blood flow.

42
Q

How does lowered venous return affect MAP?

A

As less blood gets back to the heart EDV lowers. Hence CO lowers and MAP falls. This happens steadily so you get a gradual reduction in MAP back towards normal.

43
Q

What is the bodies response to lowered MAP?

A

When MAP falls below normal (due to reduced VR) it triggers the baroreceptor reflex which makes MAP rise again

44
Q

When the valsalva manoeuvre ends the decreased thoracic pressure is transmitted to the aorta, what effect does this have on the MAP?

A

Reduces MAP significantly (large drop below resting level)

45
Q

How does returning back to normal venous return after the valsalva manoeuvre affect MAP?

A
  • After the valasalva manoeuvre thoracic pressure returns to normal so venous return does too.
  • EDV returns to normal and MAP quickly rises again.
  • Since the baroreflex is still active MAP rises well above normal
46
Q

What happens to BP after the valsalva manoeuvre after the baroreflex wears off?

A

BP returns to normal

47
Q

What is the risk to elderly who go through a valsala manoeuvre?

A

Their CVS can’t cope with the variations in MAP, particularly the sudden hypotension when thoracic pressure returns to normal (common for elderly to faint or have heart attacks)

48
Q

What hormone system regulates MAP in the long term?

A

renin-angiotensin- aldosterone system

49
Q

What effect on arterioles does angiotensin II have?

A

It causes constriction and therefore increase in TPR

50
Q

What effect does aldosterone have on cells? (2)

A
  • increase Na reabsorption

- increase in plasma volume

51
Q

What effect does vasopressin (antidiuretic) hormone have on arterioles? (4)

A
  • causes arteriolar constriction
  • increase in TPR
  • increased water permeability of collecting duct
  • increase in plasma volume
52
Q

What effect do atrial natriuretic peptide and brain natriuretic peptide have on arterioles? (4)

A
  • cause arteriolar dilation
  • decrease in TPR
  • increase in Na (natriuresis)
  • decrease in blood volume
53
Q

In summary what 3 hormone groups are involved in long term control of BP?

A
  1. renin-angiotensin- aldosterone system
  2. vasopressin (antidiuretic)
  3. atrial natriuretic peptide and brain natriuretic peptide
54
Q

What are 2 ways in which posture affects the BP?

A
  1. effect of standing

2. the reflex response

55
Q

What effect does standing have on the hydrostatic pressure?

A

Increased hydrostatic pressure causes pooling of blood in veins/ venules of feet/ legs (naturally decreases BP)

56
Q

What effect does standing have on: VR, EDV, preload, SV, CO, MAP, baroreceptor firing rate

A 
decrease VR 
decrease EDV 
decrease preload 
decrease SV 
decrease CO 
decrease MAP 
decrease baroreceptor firing rate
57
Q

What is the reflex response?

A

naturally responds to standing (adrenaline will have the same effect to it; wakes up the circulatory system by increasing the dropping BP)

58
Q

What does a DECREASE in vagal tone cause in reflex response? (putting the parasympathetic system to sleep) (2)

A
  • decrease in heart rate

- decrease in cardiac output

59
Q

What does an INCREASE in sympathetic tone cause in a reflex response? (in terms of; HR, CO, SV, VR, EDV, TPR)

A 
increase heart rate 
increase cardiac output 
increase stroke volume 
increase venous return 
increase end diastolic volume 
increase TPR 
(through vasoconstriction)
60
Q

What happens to the pressure in thorax during valsalva manoeuvre? Why does it affect MAP ultimately?

A

Increased thoracic pressure is transmitted through aorta which affects MAP ultimately

61
Q

What effect does increased thoracic pressure have on;

VR, EDV, SV, CO and MAP

A 
decrease VR 
decrease EDV 
decrease SV 
decrease CO 
decrease MAP
62
Q

What is decrease in MAP detected by? (during a valsalva manoeuvre) What do these initiate?

A

detected by baroreceptors; which initiate reflex response

63
Q

What effect does reflex response have on CO and TPR?

A
  • increase CO

- increase TPR

64
Q

Why does the valsalva manoeuvre graph continue on after BP has been stabilised and stroke volume increases once more to normal?

A

because reflex effects have not worn off

65
Q

Why can the valsalva manoeuvre be used to test a patient’s arteriobaro reflex?

A

it will continue to fall without stabilising in a patient with poor baroreflex

66
Q

In summary what are the main features of the pumping ability of the heart? (4)

A
  1. structure
  2. electrical activity
  3. cardiac cycle
  4. control of HR and SV
67
Q

What are 2 controls of arterioles and what do they control?

A
  1. Local: to meet needs of tissues

2. Central: to regulate MAP

68
Q

What is the central control of MAP?

A

arterial baroreflex system

2. Cardiovascular System (42 decks)

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