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CVS Physiology > Short term control of BP > Flashcards

Short term control of BP Flashcards

1
Q

What is MAP?

A

The driving force pushing blood through the circulation

MAP = CO x TPR

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2
Q

What happens if MAP is too low?

A

Tissue aren’t adequately perfused
- Affects brain = fainting

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3
Q

What happens if is MAP too high?

A

Hypertension
- Inc long term risk of stroke and coronary heart disease

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4
Q

Where are baroreceptors located?

A

One in aortic arch
One in carotid sinus
- At bifurcation of carotid internal and external arteries

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5
Q

What do baroreceptors do?

A

Detect changes in pressure indirectly = Are stretch receptors

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6
Q

What is a baroreceptors response to increase in pressure/stretch?

A

Increase firing rate of action potentials

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7
Q

When (normally) is pressure increase and AP firing increases?

A

During early systole when theres a rapid rise in pressure

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8
Q

What nerve are signals from baroreceptors transmitted up?

A

Aortic arch baroreceptors = vagus nerve
Carotid sinus baroreceptors = glossopharyngeal nerve

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9
Q

Where is the integrating centre for baroreceptor signals?

A

Medullary cardiovascular centres

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10
Q

What are cardiopulmonary baroreceptors?

A
  • Sensing central blood volume
  • Stretch receptors
  • Increase firing rate of AP with increased stretch (volume)
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11
Q

What do central chemoreceptors sense?

A

Arterial pCO2 and pO2
- Detect increase in CO2 and decrease in O2

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12
Q

What response does central chemoreceptors have?

A

Stimulate respiratory drive
- Increase the amount of O2 getting into the lungs
- Increase MAP

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13
Q

What do chemoreceptors in muscle sense?

A

Metabolite concentration

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14
Q

What do chemoreceptors in joints sense?

A

Joint movement

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15
Q

What does the hypothalamus do?

A

Coordinating vascular response for thermoregulation
Coordinating fight or flight

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16
Q

What does the cerebral cortex do?

A

Strong emotional stimuli can trigger CVS response
Vasovagal syncope = fainting at sight of blood or a needle

17
Q

What responses can the medullary CV centre have to bring MAP back to normal values?

A
  • Parasympathetic outflow via vagus nerve innervating the sinoatrial node in the heart.
  • Sympathetic nerves innervating sinoatrial node in heart
  • Sympathetic nerves innervating muscle of ventricle
  • Release of adrenaline and noradrenaline into the blood
18
Q

What nerve fibres carry parasympathetic innervation and where do they innervate?

A

Vagus nerve
- Sinoatrial node in heart

19
Q

What neurotransmitter is released by Parasympathetic fibres and what does it bind to?

A

Acetylcholine - muscarinic receptors on pacemaker cells

20
Q

What is the effect of parasympathetic innervation of the SA node?

A

Hyperpolarisation of pacemaker cells
- means they take longer to reach threshold
Decreased HR (bradycardia)
No effect on contractility (as not innervating muscle)

21
Q

What neurotransmitter is released by sympathetic nerves innervating the SA node and where does it bind?

A

Noradrenaline - B1 receptors

22
Q

What affect does noradrenaline binding to B1 receptors have?

A

Pacemaker cells depolarise faster
Increased HR

23
Q

What is the effect of sympathetic innervation of the myocardium?

A

Increased contractility and thus stroke volume

24
Q

How is contractility increased by sympathetic innervation?

A

Increased release of calcium
- More actin and myosin cross bridges forming
- Increased strength of contraction

25
Q

What does adrenaline and noradrenalin released into the bloodstream bind to?

A

B1 receptors
A1 receptors on smooth muscle of blood vessels

26
Q

What is the result of noradrenaline and adrenaline in bloodstream binding to B1 receptors?

A

Increased HR and increased contractility

27
Q

What is the result of noradrenaline and adrenaline in bloodstream binding to A1 receptors?

A

Smooth muscle contraction = vasoconstriction
- Pushes more blood back to the heart giving increased EDV & preload, stronger fore of contraction, larger SV, increased CO and thus MAP

(arteriolar constriction = resistance vessels = increases TPR = increases MAP)

28
Q

What is the Valsalva manoeuvre?

A

Forced expiration against a closed glottis

29
Q

What is the Valsalva manoeuvre used for (physiological)?

A

Defecation
Lifting heavy things
Popping ears

30
Q

What happens to BP throughout the Valsalva manoeuvre?

A

Increases immediately
Slow decrease
Reduced BP
Drop in BP
Massive rebound increase in BP

31
Q

What happens in phase 1 of the Valsalva manoeuvre?

A

Increased thoracic pressure is transmitted through to aorta - hence immediate jump

32
Q

What happens in phase 2 of the Valsalva manoeuvre

A

Increased thoracic pressure reduced the filling pressure from the veins (making it harder for blood to get back to heart) which therefore:
- Reduces venous return, EDV and preload
- Starlings law = reduced preload then less efficient excitation-contraction coupling, fewer cross bridges forming, reduced force of contraction so stroke volume falls.
- SV & CO fall
- MAP will fall

33
Q

What happens in late phase 2 of the Valsalva maneuovre?

A

The reduced MAP will be detected by baroreceptors in carotid sinus and aortic arch which initiate a reflex increase in CO and TPR

34
Q

How is a reflex increase in CO and TRP brought about in the Valsalva manoeuvre?

A
  • Increases sympathetic tone
  • Increased release of noradrenaline from sympathetic nerves that bind to beta 1 receptors o sinoatrial node
  • Increases HR
  • Increased contractility and so you get vasoconstriction (More blood is pushed back to heart and EDV increases)
  • Arteriolar constriction = increases TPR
35
Q

What happens in phase 3 of the Valsalva manoeuvre?

A

At end of manoeuvre, the decrease in thoracic pressure is transmitted through to the aorta, hence the drop in BP

36
Q

What happens in phase 4 of the Valsalva Manoeuvre?

A

Massive increase in BP (rebound)
- When doing manoeuvre blood was stopped from getting back to heart so was accumulating in veins
- When stop manoeuvre blood comes flooding back

37
Q

What happens in phase 5 of the Valsalva manoeuvre?

A

Venous return restored/increased
- Massive increase in SV
- Now tries to decrease Map via increased vagal tone
- More acetylcholine released from vagus nerve
- Acting on cholinergic muscarinic receptors and slow down sinoatrial node
- Decrease in HR
- Leading to decreased CO

38
Q

What is the clinical significance of the Valsalva manoeuvre?

A

Used as a test of autonomic function

39
Q

When can Valsalva manoeuvre be reduced?

A

Older people
- BP is not restored by baroreflex
Autonomic neuropathy
- e.g. damage due to diabetes
- Reduced baroreflex

CVS Physiology (10 decks)

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