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brs 6: cardiovascular and respiratory medicine > 6.14: Control of heart function > Flashcards

6.14: Control of heart function Flashcards

1
Q

Function and location of Sinoatrial node

A

Pacemaker of the heart 60-100bpm
Junction of crista terminalis; upper wall of right atrium and opening of superior vena cava

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2
Q

Function and location of Atrioventricular node

A

Has pacemaker activity : slow calcium mediated action potential
Triangle of Koch at base of right atrium

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3
Q

What are the main tracts in the heart

A

Bundle of His and bundle branches - specialised myofibres
Purkinje fibres - conducting fibres

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4
Q

Nodal cell action potential (AP)

A

Upstroke - due to calcium influx
Repolarisation- due to K+ efflux
Nodal cells do not have a resting potential, only pre-potential due to Na+ influx through a funny channel

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5
Q

3 phases of nodal cell action potential

A

Phase 0 - upstroke
Phase 4 - pre-potential
Phase 3 - repolarisation

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6
Q

Why do different parts of the heart have different action potential shapes

A

Different ion currents flowing and different ion channel expression in cell membrane

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7
Q

What is cardiac AP like compared to nerves

A

Long 200-300ms vs 2-3ms

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8
Q

Duration of an action potential controls

A

Duration of heart contraction

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9
Q

What type of contraction is required to produce an effective pump

A

Long, slow contraction

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10
Q

Phases of cardiac muscle action potential

A

Phase 0 - upstroke
Phase 1- early repolarisation
Phase 2- plateau
Phase 3- repolarisation
Phase 4- resting membrane potential

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11
Q

Absolute refractory period is the time during which

A

No AP can be initiated

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12
Q

Relative refractory period is the period after

A

ARP
Where an AP can be elicited but only with larger stimulus strength

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13
Q

What part of the CNS controls the heart

A

Autonomic nervous system - cardio-regulatory centre and vasomotor centre in medulla

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14
Q

Effects of the parasympathetic nervous system on heart control

A

Rest and digest
Decreases heart rate - decr. Slope of phase 4

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15
Q

Effects of sympathetic nervous system on heart control

A

Fight or flight
Increases heart rate (chronotropy) - increases the slope of phase 4
Increases force of contraction (initropy) increases Ca2+ dynamics

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16
Q

Where do parasympathetic neurones arise from

A

Cranial part of spinal cord
Sacral part of spinal cord

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17
Q

Where do sympathetic neurones arise from

A

Thoracic vertebrae
Lumbar vertebrae

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18
Q

What neurotransmitter do Parasympathetic pre- and post ganglionic fibres use

A

ACh
-important for heart rate control

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19
Q

What neurotransmitter do sympathetic pre and post ganglionic neurones use

A

Pre : ACh
Post : NA
Important for control of circulation

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20
Q

Where vasomotor centre located

A

Bilaterally in reticular substance of medulla and lower third of pons

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21
Q

What is the vasomotor centre composed of

A

Vasoconstrictor area (pressor)
Vasodilator area (depressor)
Cardio-regulatory inhibitory area

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22
Q

What does the vasomotor centre transmit impulses through and to

A

Distally through spinal cord to almost all blood vessels

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23
Q

What can exert powerful excitatory or inhibitory effects on the VMC

A

Higher centres of brain e.g hypothalamus

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24
Q

What do the lateral portions of VMC control, how

A

Heart activity by influencing heart rate and contractility

25
Q

What does the medial portion of the VMS transmit signals via and to

A

Vagus nerve to heart
Decrease heart rate

26
Q

What nerves are involved in the renal system

A

Sympathetic nerves

27
Q

How is an increase in renal activity brought about

A

Decrease in glomerular filtration
Decrease in Na+ excretion
Increase in blood volume (aldosterone)

28
Q

What is kidney blood volume detected by

A

Venous volume receptor

29
Q

How is a decrease in renal activity brought about

A

Increased renin secretion
Increased angiotensin-II production
Vasoconstriction
Increased blood pressure

30
Q

What receptors is blood pressure in the kidneys detected by

A

Arterial baroreceptors

31
Q

Where do sympathetic nerve fibres innervate the kidneys

A

Innervate afferent and efferent arterioles of glomerulus (and nephron tube cells)

32
Q

How does the sympathetic nervous system bring about a response in the kidneys

A

Afferent arterioles are the primary site of sympathetic activity
a1-adrenoreceptor induces vasoconstriction
Decrease in glomerular filtration rate
Less Na+ filtered
Juxtaglomerular cells are site of synthesis, storage and release of renin
b1-adrenoreceptor leads to renin secretion

33
Q

The cardiopulmonary circuit consists of

A

Large pulmonary vessels

34
Q

How is the cardiopulmonary circuit regulated

A

Volume sensors (atria, right ventricle) send signals through glossopharyngeal and vagus nerves

35
Q

What does a Decrease in filling of the heart causes (cardiopulmonary circuit)

A

Decreased baroreceptor firing
Increased sympathetic nervous activity

36
Q

Distension of cardiopulmonary circuit leads to

A

Increased baroreceptor firing
Decreased SNS activity

37
Q

The arterial circuit consists of

A

Aortic arch
Carotid sinus
Afferent arterioles of kidneys

38
Q

What do the Pressure sensors in the arterial circuit send signals through

A

Send signals through glossopharyngeal and vagus nerves

39
Q

What does a decrease in pressure in the arterial circuit lead to

A

Decreased baroreceptor firing
Increased SNS activity

40
Q

What does an increase in pressure of the arterial circuit lead to

A

Increased baroreceptor firing
Decreases SNS activity

41
Q

Two circulations of cardiopulmonary system

A

Systemic
Pulmonary

42
Q

What is venous volume distribution affected by

A

Peripheral venous tone
Gravity
Skeletal muscle pump
Breathing

43
Q

Central venous pressure determines the

A

Amount of blood flowing back to the heart

44
Q

The amount of blood flowing back to the heart determines

A

Stroke volume ( using starlings law of the heart)

45
Q

In veins, constriction reduces and increases

A

Reduces compliance
Increases venous return

46
Q

In arterioles, constriction determines

A

Blood flow to downstream organs
Mean arterial blood pressure
The pattern of blood flow to organs

47
Q

Why are local mechanisms essential in regulating blood flow

A

(Intrinsic to smooth muscle)
Important for reflex local blood flow regulation within an organ

48
Q

4 endothelium derived mediators include :

A

Nitric oxide
Prostacyclin
Thromboxane A2
Endothelins

49
Q

How does Nitric oxide act as a local blood flow mediator

A

Potent vasodilator
Diffuses into vascular smooth muscle cells

50
Q

How does prostacyclin act as a local blood flow mediator

A

Vasodilator
Has antiplatelet and anticoagulant effects

51
Q

How does TXA2 act as a local blood flow mediator

A

Vasoconstrictor
Heavily synthesised in platelets

52
Q

How do endothelins act as a local blood flow mediator

A

Vasoconstrictors
Generated from nucleus of endothelial cells

53
Q

Characteristics of Systemic mechanisms in regulating blood flow

A

Extrinsic to smooth muscle
Include autonomic nervous system and circulating hormones

54
Q

5 non-endothelium derived mediators

A

Kinins
Atrial natriuretic peptide
Vasopressin (ADH)
Noradrenaline / Adrenaline
Angiotensin II

55
Q

How do kinins act as a systemic blood flow mediator

A

Bind to receptors on endothelial cells and stimulate NO synthesis
Vasodilator effects

56
Q

How does ANP act as a systemic blood flow mediator

A

Secreted from atria in response to stretch
Vasodilator effects to reduce BP

57
Q

How does ADH act as a systemic blood flow mediator

A

Secreted from pituitary gland
Binds to V1 receptors on smooth muscle to cause vasoconstriction

58
Q

How do noradrenaline / adrenaline act as a systemic blood flow mediator

A

Secreted from adrenal gland
Vasoconstriction

59
Q

How does angiotensin II act as a systemic blood flow mediator

A

Potent vasoconstrictor from renin-angiotensin-aldosterone axis
Stimulates ADH secretion

brs 6: cardiovascular and respiratory medicine (12 decks)

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