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BRS Cardio & Respiratory > Control of Heart function > Flashcards

Control of Heart function Flashcards

1
Q

What are the ways that cardiac function in the physiological setting is influenced?

A

Endogenous regulation (within the heart)

Exogenous regulation (outside the heart)

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2
Q

What are the exogenous regulations of cardiac function?

A

brain, kidneys, vessels

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3
Q

What can a prolonged or occasional acute imbalance in the mechanisms of control of cardiac function lead to?

A

pathophysiological consequences

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4
Q

The main anatomical components of the heart can be categorised broadly into what 3 categories?

A
  1. Muscle cells (cardio-myocytes): can contract and relax in response to electrical stimuli. Essential for pumping blood around the body
  2. Specialised electrical cells: cells that create spontaneous currents and those that transmit currents exist within the heart. Essential for regulating contraction of the cardio-myocytes
  3. Vessels: the major blood vessels are responsible for transporting blood in and out of the heart, whilst the coronary blood vessels are responsible for supplying blood to the heart
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5
Q

Which out of the three categories is the most prominent in controlling function?

A

specialised electrical cells

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6
Q

What are the nodes in the heart?

A

Sinoatrial node (SAN)

Atrioventricular node (AVN)

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7
Q

What are the tracts that connect the nodes?

A

Bundle of His and bundle branches

Purkinje fibres

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8
Q

What is the SAN?

A

Sinoatrial (SA) node
Pacemaker of the heart: 60-100 bpm
In the junction of crista terminalis; upper wall of right atrium & opening of superior vena cava

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9
Q

What is the AVN?

A

Atrioventricular (AV) node
Has pacemaker activity: slow calcium mediated action potential
Triangle of Koch at base of right atrium

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10
Q

What is the bundle of His and bundle branches?

A

Bundles of His & bundle branches

Specialised myocytes. AV node: His bundle -> branches at intraventricular septum -> apex

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11
Q

What are the purkinje fibres?

A

specialised conducting fibres

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12
Q

What are the 3 phases of the nodal cell action potential?

A

0, 3, and 4

4= pre-potential
0= upstroke
34=repolarisation

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13
Q

What is the upstroke due to in the nodal cell action potential?

A

due to Ca2+ influx

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14
Q

What is the repolarisation due to in the nodal cell action potential?

A

due to K+ efflux

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15
Q

What is the resting membrane potential of nodal cells?

A

Nodal cells do not have a resting membrane potential - only a pre-potential due to Na+ influx through a ‘funny’ channel

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16
Q

What are the action potential profiles?

A

Different parts of the heart have different action potential shapes

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17
Q

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

A

it is caused by different ion currents flowing and different ion channel expression in cell membrane

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18
Q

What is the action potential profile of…
SAN
AVN
atrial myocardium
bundle of His
endocardium
myocardium
epicardium

A
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19
Q

What are the phases of a cardiac muscle action potential?

A

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

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20
Q

How long is a nerves AP and and how long is a cardiac AP?

A

200-300 ms= cardiac
2-3 ms= nerves

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21
Q

What does duration of AP control?

A

duration of contraction of the heart

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22
Q

What is required to produce an effective pump?

A

long, slow contraction

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23
Q

What is the absolute refractory period (ARP)?

A

time during which no AP can be initiated regardless of stimulus intensity

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24
Q

What is the relative refractory period (RRP)?

A

Period after ARP where an AP can be elicited but only with larger stimulus strength

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25
Q

What is the membrane potential (mV) to Time (ms) graph look like for a ventricular cell and what is the cell permeability to ions throughout it?

A
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26
Q

What is the membrane potential (mV) to Time (ms) graph look like for a SA node cell and what is the ell permeability to ions throughout it?

A
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27
Q

What connects the AVN and SAN?

A

Internodal tracts

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28
Q

What part, blue or green under the graph represents the absolute and the relative refractory period?

A

Blue= absolute
green= relative

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29
Q

What are the 3 major organs that control function of the heart?

A

brain/ central nervous system

kidneys

blood vessels

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30
Q

How does the brain control the heart?

A

it can effect immediate changes through nerve activity or slower changes through hormonal activity

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31
Q

How does the kidney control the heart?

A

the heart and kidneys share a bi-directional regulatory relationship usually through indirect mechanisms

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32
Q

How does the blood vessels control the heart?

A

by regulating the amount of blood that goes to and from the heart the blood vessels are able to influence cardiac activity

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33
Q

Where is the cardio-regulatory centre and vasomotor centre?

A

In the medulla

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34
Q

How is the nervous system divided in humans?

A
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35
Q

What division of the nervous is control of the heart?

A

autonomic nervous system

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36
Q

What does the parasympathetic nervous system do?

A

‘Rest & digest’
decrease heart rate (HR) – decreases the slope of phase 4

37
Q

What does the sympathetic nervous system do?

A

‘fight or flight’

increase HR (chronotropy) – increases the slope of phase 4

increase force of contraction (inotropy) – increases Ca2+ dynamics

38
Q

What nerve connects the medulla to the heart for parasympathetic nervous system innervation?

A

Vagus

39
Q

What nerve connects the medulla to the heart for sympathetic nervous system innervation?

A

sympathetic nerves

40
Q

How do the graphs of membrane potential to time differ between para and sympathetic stimulation?

A
41
Q

What is the parasympathetic nervous system particularly important for?

A

controlling the heart rate

42
Q

What is the sympathetic nervous system particularly important for?

A

controlling the circulation

43
Q

What are the neurotransmitters used in the parasympathetic NS?

A

Pre-ganglionic fibres use ACh as neurotransmitter

post ganglionic NT = ACh

44
Q

What are the neurotransmitters used in the sympathetic NS?

A

Pre-ganglionic fibres use ACh as their neurotransmitter

Post ganglionic NT = NA

45
Q

Where do parasympathetic and sympathetic nerves arise from

A

Para= cranial part of spinal cord and sacral part of spinal cord

Sympathetic= thoracic vertebra, lumbar vertebra

46
Q

What are the receptors for the neurotransmitters in parasympathetic fibres?

A

Nicotinic receptors (preganglionic) and Muscarinic receptors (post ganglionic)

47
Q

What are the receptors for the neurotransmitters in sympathetic fibres?

A

Nicotinic receptors (preganglionic) noradrenaline receptors (post ganglionic)

48
Q

What is the vasomotor centre composed of?

A

Composed of:
Vasoconstrictor (pressor) area
Vasodilator (depressor) area
Cardio-regulatory inhibitory area

49
Q

Where is the vasomotor centre located?

A

VMC located bilaterally in reticular substance of medulla & lower third of pons

50
Q

What does the vasomotor centre do?

A

Transmits impulses distally through spinal cord to almost all blood vessels

51
Q

What can exert excitatory/ inhibitory effects on the vasomotor centre?

A

Many higher centers of the brain such as the hypothalamus can exert powerful excitatory or inhibitory effects on the VMC.

52
Q

What do the lateral portions of the vasomotor centre control?

A

Lateral portions of VMC controls heart activity by influencing heart rate and contractility

53
Q

What does the medial portion of the vasomotor centre do?

A

Medial portion of VMC transmits signals via vagus nerve to heart that tend to decrease heart rate.

54
Q

How does parasympathetic and sympathetic cardiac innervation change heart rate, shown in a graph?

A
55
Q

In the parasympathetic nervous system, is the preganglionic or postganglionic fibre longer?

A

preganglionic is longer

56
Q

In the sympathetic nervous system, is the preganglionic or postganglionic fibre longer?

A

postganglionic fibre is longer

57
Q

Where do the sympathetic nerve fibres tend to synapse?

A

sympathetic ganglia/ paravertebral ganglia

58
Q

How does parasympathetic cardiac innervation work?

A

1) Acetylcholine acts on M2-receptors (muscarinic receptors) on cell membrane of a SAN cell

2) Gi protein causes inhibition of adenylyl cyclase

3) prevents conversion of ATP-> cAMP-> PKA

Inhibition of the secondary messenger

59
Q

How does sympathetic cardiac innervation work?

A

1) noradrenaline acts on B1-receptors

2) Gs protein promotion causing the promoting of adenylyl cyclase

3) promoting ATP-> cAMP-> PKA

Opposite of parasympathetic

60
Q

What does angiotensin II also cause to be secreted?

A

aldosterone from adrenal glands

61
Q

What happens to the renal system with afferent sympathetic nerve innervation?

A

Decrease glomerular filtration-> decrease Na+ excretion:
increase in blood volume
(aldosterone also plays a role in increasing blood volume)

62
Q

What detects changes in blood volume?

A

venous volume receptors

63
Q

What caused renin secretion, and what does renin secretion cause?

A

Sympathetic nerves

Increased renin secretion-> increased angiotensin-II production:
leading to vasoconstriction & increased blood pressure

64
Q

What detects changes in blood pressure?

A

arterial baroreceptors

65
Q

How does the sympathetic nerves, blood volume and blood pressure all link to cause a change in blood pressure?

A
66
Q

What innervates afferent and efferent arterioles of the glomerulus (and nephron tubule cells)?

A

sympathetic nerve fibres

67
Q

What happens at the afferent arterioles?

A

Primary site of sympathetic activity:

a1-adrenoceptor -> vasoconstriction
decreases glomerular filtration rate -> decrease Na+ filtered

68
Q

How do sympathetic nerves affect juxtaglomerular cells?

A

Juxtaglomerular cells are the site of synthesis, storage & release of renin
B1-adrenoceptor-> renin secretion
subsequently increasing aldosterone secretion
which increases blood volume

69
Q

What happens with a1-receptors in the glomerular afferent arterioles?

A

noradrenaline acts on a1-receptor
causes Gq to activate PLC

leading to…

PIP2–> DAG–> PKC

PIP2-> IP3-> Ca2+

70
Q

WHat happens to B1 receptors in juxtaglomerular cells?

A

noradrenaline acts on B1-receptors
causes Gs to activate AC

leading to ATP-> cAMP-> PKA

71
Q

What is the cardiopulmonary circuit made of?

A

Large pulmonary vessels

72
Q

How does the cardiopulmonary circuit work?

A

Volume sensors (also atria & right ventricle): send signals through glossopharyngeal & vagus nerves

Decrease in filling -> decreased baroreceptor firing -> increased sympathetic nerve (SNS) activity

Distention -> increased baroreceptor firing -> decreased SNS activity

73
Q

What is the arterial circuit made of?

A

Aortic arch, carotid sinus & afferent arterioles of kidneys

74
Q

How does the arterial circuit work?

A

Pressure sensors: send signals through glossopharyngeal & vagus nerves

Decrease in pressure -> decreased baroreceptor firing -> increased SNS activity

Increase in pressure -> increased baroreceptor firing -> decreased ISNS activity

75
Q

What are the 2 circulation of the heart?

A

pulmonary and systemic

76
Q

What is the order of circulation?

A

right heart-> lungs-> left heart-> body

77
Q

What is venous volume distribution affected by?

A

peripheral venous tone, gravity, skeletal muscle pump and breathing

78
Q

What is central venous pressure?

A

Mean pressure in the right atrium
It determines amount of blood flowing back to heart

79
Q

What does the amount of blood flowing back to the heart determine?

A

stroke volume (using starling’s law of the heart)

80
Q

What does constriction in veins lead to?

A

reduces compliance and increases venous return

81
Q

In arterioles what does constriction determine?

A

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

82
Q

What is the blood distribution around the heart?

A
83
Q

What is the control of venous return like?

A
84
Q

What are the local mechanisms of regulating blood flow? (4)

A

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

Endothelium-derived mediators include:

  • Nitric oxide (NO): potent vasodilator, which diffuses into vascular smooth muscle cells.
  • Prostacyclin: vasodilator that also has antiplatelet & anticoagulant effects
  • Thromboxane A2 (TXA2): vasoconstrictor that is also heavily synthesised in platelets
  • Endothelins (ET): vasoconstrictors generated from nucleus of endothelial cells
85
Q

What are the systemic mechanism for regulating blood flow? (5)

A

Extrinsic to the smooth muscle
These include the autonomic nervous system & circulating hormones

Non-endothelium-derived mediators include:

  • Kinins: bind to receptors on endothelial cells & stimulate NO synthesis – vasodilator effects
  • Atrial natriuretic peptide (ANP): secreted from the atria in response to stretch – vasodilator effects to reduce BP
  • Vasopressin (ADH): secreted from pituitary gland. Binds to V1 receptors on smooth muscle to cause vasoconstriction
  • Noradrenaline/Adrenaline: secreted from adrenal gland (& SNS); causes vasoconstriction
  • Angiotensin II: potent vasoconstrictor from the renin-angiotensin-aldosterone axis. Also stimulates ADH secretion.
86
Q

What is inotropy and chronotropy?

A

inotropy= muscle contraction

chronotropy= heart rate

87
Q

What effect will activation of renal arteriole alpha-1 receptor eventually have on the heart, chronotropy and inotropy wise?

A

Reduced chronotropy & increased inotropy

This is most likely to happen if we are only taking into account the Starling forces on the heart (increased volume –> increased force of contraction) and the effects on the baroreceptors (increased volume and pressure –> reduced SNS activity)

88
Q

When does baroreceptor firing increase?

A

When pressure increases

BRS Cardio & Respiratory (28 decks)

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