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BRS (RF) > Control of heart function > Flashcards

Control of heart function Flashcards

1
Q

Which cerebral centre exerts neural control on the heart?

A

Cardioregulatory centre and vasomotor centre

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2
Q

Where is the cardio regulatory centre located?

A

Medulla oblongata

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3
Q

Which nervous branch decreases heart rate and exerts negative ionotropy?

A

Parasympathetic system

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4
Q

What is chronotrophy?

A

Heart rate

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5
Q

Where do the parasympathetic fibres arise from?

A

The craniosacral region

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6
Q

Which neurotransmitter is secreted from parasympathetic preganglionic neurones?

A

Acetylcholine

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7
Q

What type of synapse is present at parasympathetic nerve terminals?

A

Cholinergic

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8
Q

Which receptors do acetylcholine bind onto at preganglionic nerve junctions?

A

Nicotinic receptors

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9
Q

Which receptors do acetylcholine bind onto at post-ganglionic nerve junctions?

A

Muscarinic receptors

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10
Q

Where are muscarinic receptors located?

A

M2 heart

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11
Q

What effect does stimulation on muscarinic receptors have on the heart?

A

Negative chronotropy

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12
Q

What effects does sympathetic activity exert onto the heart?

A

Increase in heart rate (positive chronotropy)- elevates phase 4 slope
Increases force of contraction (Ionotrophy)- increase calcium dynamics

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13
Q

Where do the sympathetic fibres arise from?

A

Thoracolumbar region

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14
Q

Which neurotransmitter is released from sympathetic preganglionic terminals?

A

Acetylcholine

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15
Q

Which neurotransmitter is released from sympathetic postganglionic fibres?

A

Noradrenaline (NA)

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16
Q

Where is the vasomotor centre located?

A

Bilaterally in reticular substance of the medulla and lower third of pons

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17
Q

Which cerebral centres exert excitatory and inhibitory effects onto the vasomotor centre?

A

Limbic system (Hypothalamus, cingulate gyrus, amygdala, hippocampus, and thalamus)

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18
Q

Which regions of the brain influence heart rate and contractility?

A

Lateral regions

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19
Q

What influences does the medial cerebral regions exert on the heart?

A

Parasympathetic nervous system - negative chronotropy

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20
Q

Which nerve is associated with parasympathetic nervous transmission?

A

Vagus nerve

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21
Q

What are the three main functions of the vasomotor centre?

A

Vasoconstrictor
Vasodilator
Cardioregulatory inhibitory area

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22
Q

Which cardiac structure do the parasympathetic and sympathetic branches both innervate?

A

Sinoatrial node (SAN)

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23
Q

Which cardiac receptors are stimulated by sympathetic activity

A

beta-1 receptors

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24
Q

What type of receptor are b1 receptors?

A

GS-linked proteins

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25
Q

Upon sympathetic activity what pathway is triggered within cardiac cell?

A

Activation of adenyl cyclase, increases the activity of cyclic-amp and protein kinase A, secondary messenger pathway

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26
Q

What effect does cAMP have on cardiac SAN cells?

A

Molecular regulation of ion channels, influences heart rate and contractility.

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27
Q

What is the relationship between cAMP levels and sympathetic innervation?

A

Sympathetic innervation positively correlates with cAMP intracellular concentrations

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28
Q

Which type of cardiac receptors are innervated by parasympathetic activity?

A

M2 receptors

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29
Q

What type of receptors are M2 cardiac receptors?

A

G-I linked (inhibitory) , reduces levels of cAMP, and adenyl cyclase activity.

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30
Q

What effect is exerted by parasympathetic innervation onto the heart?

A

Reduces impact of positive chronotropy and ionotropy.

Heart rate and contractility decreases

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31
Q

How does the removal of sympathetic innervation to the heart affect heart rate?

A

Reduction to heart rate

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32
Q

What is the underlying tonic relationship between parasympathetic and sympathetic control?

A

Parasympathetic nervous system is more active under tonic/rest conditions.
Both branch removal results in an overall increase in heart rate

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33
Q

What effect does increased sympathetic nerves have on the kidney?

A

Decrease glomerular filtration rate. reducing sodium secretion
NA release causes afferent arteriole constriction
JG cells secrete renin

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34
Q

How is the glomerular filtration rate (GFR) affected by increased sympathetic activity?

A

Reduction in sodium secretion into tubular system, therefore favouring sodium retention, this increases water retention and blood volume (blood pressure increases)

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35
Q

What are afferent arterioles?

A

Afferent arterioles deliver blood via the renal artery, branching within the Bowman’s capsule of the glomerulus

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36
Q

What is the role performed by efferent arterioles?

A

Efferent arterioles remove blood from nephron, associated with peritubular capillaries

37
Q

What sympathetic effect is exerted onto afferent arterioles?

A

Increased sympathetic activity increases the release of noradrenaline from post-ganglionic terminals, hence acting on alpha-1 receptors.

Vasoconstriction on arterioles, reduced blood flow into glomerulus less sodium into the nephron system

38
Q

Which receptors present on the afferent arteriole are influenced by sympathetic activity?

A

Alpha-1

39
Q

What happens to afferent arterioles upon sympathetic activity?

A

Vasoconstriction

40
Q

Where do juxta-glomeular cells reside?

A

Reside proximal to afferent arteriole.

Within the distal convoluted tubule

41
Q

Which receptors innervated by the sympathetic nervous system affect JG cells?

A

Beta-1

42
Q

What effect does increased sympathetic activity on JG cells exert?

A

Increased renin secretion

43
Q

What parasympathetic activity is exerted onto the kidney?

A

None

44
Q

How is blood volume detected?

A

Venous volume receptor

45
Q

What effect does secreted renin exert?

A

Catalyses the conversion of angiotensinogen into angiotensin-1 –> angiotensin-II –> increased aldosterone release –> increased blood pressure

46
Q

What effect is exerted by angiotensin-II?

A

Vasoconstrictor, thus increasing blood pressure

47
Q

How is blood pressure detected?

A

Arterial baroreceptors

48
Q

Where are arterial baroreceptors located?

A

Aortic arch,

carotid sinus

49
Q

Which nerves transmit sensory stretch signals?

A

Glossopharyngeal and vagus nerve

50
Q

What effect does reduced diastolic filling have?

A

Reduction volume activates sensory stimulation of baroreceptor, reduction in baroreceptor firing, increases sympathetic activity

51
Q

What is distention?

A

Distention: Increased filling and volume

52
Q

What effect does distension have?

A

Increased baroreceptor firing, decreased SNS activity

53
Q

What are the two circulation systems?

A

Pulmonary and systemic

54
Q

How is venous volume distribution affected?

A

Affected by peripheral venous tone, gravity , muscle pump & breathing

55
Q

What is central venous pressure?

A

Mean pressure in the right atrium, determines amount of blood return to heart

56
Q

What effect does venous return have on cardiac output?

A

Increased diastolic volume increased preload, increasing preload subsequently increases contractility
Starlings law.

57
Q

What effect does vasoconstriction in veins have?

A

Reduced compliance

Reduced venous return

58
Q

What effect does arteriole vasoconstriction have?

A

Increased arteriole constriction results in elevated BP, therefore influencing afterload

Blood flow to downstream organs

Mean arterial blood pressure

Pattern of blood flow to organs

59
Q

What are intrinsic mechanisms of blood flow regulation?

A

Vasodilator and vasoconstrictor release from local endothelial cells.

60
Q

Name the intrinsic vasodilators

A

Nitric oxide

Prostacyclin

61
Q

What effect does prostacyclin have?

A

Vasodilator expresses anti platelet and anticoagulant effects

62
Q

What effects does NO have?

A

Potent vasodilator, diffuses into vascular smooth muscle cells

63
Q

Name the intrinsic vasoconstrictors:

A

Thromboxane 2

Endothelin

64
Q

Where is Thromboxane A2 produced?

A

Synthesised by cyclo-oxygenase activity from activated platelets

65
Q

What are systemic mechanisms of blood flow regulation?

A

Extrinsic to smooth muscle, impacts blood pressure and volume. These include autonomic nervous system and circulating hormones

66
Q

Name the vasodilator extrinsic mediators:

A

Kinins,

Atrial natriuretic peptide (ANP)

67
Q

What are extrinsic mediators?

A

Non-endothelial derived mediators

68
Q

What effect do kinins have?

A

Kinins bind to endothelial cell receptors, stimulates NO synthesis, expressing vasodilator effects

69
Q

Why is ANP secreted?

A

Response to high afterload and increased diastolic volume (stretch), attempts to reduce blood pressure

70
Q

Name the extrinsic vasoconstrictors:

A

Vasopressin
NA/Adrenaline
Angiotensin-II

71
Q

Which receptors does ADH bind onto on arterioles?

A

V1 receptors

72
Q

Where is the SAN located?

A

Junction of crest terminals, upper wall of right atrium, opening of the superior vena cava.

73
Q

Where do the branches form the Bundle of His traverse?

A

Intraventricular septum

74
Q

What are Purkinje fibres?

A

Specialised conducting fibres, transmitting electrical impulses to stimulate ventricular systole

75
Q

What is the cardiac electrical pattern (action potential)?

A

Rapid depolarisation –> plateau phase –> Repolarisation

76
Q

How many phases are associated with the cardiac action potential?

A

5 (0-4)

77
Q

What is phase 0?

A

Upstroke

78
Q

What is phases 1-4?

A

Early repolarisation, plateau phase, repolarisation, resting membrane potential

79
Q

How are action potentials transmitted throughout cardiomyocytes?

A

Action potentials are transmitted through gap junctions. Cell to cell ion flow.

80
Q

What occurs during upstroke?

A

Fast voltage-gated ion channels rapidly open. Causes sodium influx along electrochemical and concentration gradients

81
Q

What happens during the plateau phase?

A

Membrane potential declines relatively slow, due to opening of slow Calcium L-type voltage gated channels (L=latent)
Enables calcium influx, potassium channel open, potassium efflux

82
Q

The influx of which ion is associated with the plateau phase?

A

Calcium ion

83
Q

Which type of calcium ion channel is associated with the plateau phase?

A

L-type voltage gated calcium channels

84
Q

When do the L-type calcium ion channel close?

A

When the membrane potential reaches zero

85
Q

What occurs during repolarisation?

A

Membrane potential reaches resting potential

86
Q

When does the absolute refractory period occur?

A

Occurs during the plateau phase.

87
Q

What is the absolute refractory phase?

A

Action potentials are not stimulated in response to stimuli, prevents the possibility of tetany

88
Q

How long is the absolute refractory period?

A

200ms

89
Q

What is the relative refractory period?

A

Subsequent contraction corresponds to the repolarisation phase. Buffer period, greater action potential required to overcome the RRP. Larger stimulus required to trigger action potential

BRS (RF) (38 decks)

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