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2.6 BRS Cardiovascular & Respiratory > Control of Heart > Flashcards

Control of Heart Flashcards

1
Q

What are the 2 nodes of the heart?

A
  1. Sinoatrial (SA) node
    • pacemaker —> 60-100 bpm
    • location - junction of crista terminalis (right atrium
      upper wall) —> superior vena cava
      opening
  2. Atrioventricular (AV) node
    • pacemaker activity —> via slow Ca2+ mediated AP
    • location - triangle of Kotch (right atrium base)
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2
Q

What are the 3 tracts of the heart?

A
  1. Internodal tracts - SA to AV node
  2. Bundles of His - AV node to apex
  3. Purkinje fibres - apex to ventricles (upwards)
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3
Q

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

A
  1. Phase 4 —> upstroke (-60 to -40mV)
    - Na+ influx via funny channels
    - gradual inc —> lasts 300ms
  2. Phase 0 —> pre-potential (-40 to +20mV)
    - Ca2+ influx
    - straight up
  3. Phase 3 —> repolarisation (+20 to -60mV)
    - K+ efflux
    - gradual dec —> lasts 700ms
  • AP for 2-3ms (phase 0)
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4
Q

What are the 7 types of cells generating action potential in the heart?

A
  1. SA node
  2. Atrial myocardium
  3. AV node
  4. Bundle of His
  5. Endocardium
  6. Myocardium
  7. Epicardium
    - all different action potential profiles ∵ different ion
    currents + different ion channel expression
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5
Q

What are the 5 phases of ventricular cardiomyocyte action potential profile?

A
  1. Phase 0 —> upstroke (-90mV to +40mV)
    - Na+ influx
    - straight up
  2. Phase 1 —> early repolarisation (+40mV to 0mV)
    - K+ efflux
    - fast dec (lasts 50ms)
  3. Phase 2 —> plateau (0mV)
    - Ca2+ influx
    - straight across (lasts 125ms)
  4. Phase 3 —> repolarisation (0 to -90mV)
    - K+ efflux inc
    - gradual dec (lasts 95ms —> 270ms)
  5. Phase 4 —> resting membrane potential (-90 mV)
    - K+ efflux dec
    - straight across (lasts 30ms)
  • AP for 200-300ms —> duration of ventricular
    contraction
  • ARP —> phases 0, 1, 2
    RRP —> pase 3
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6
Q

What is ARP vs RRP?

A

ARP = Absolute Refractory Period
—> no AP can be generated
- phases 0, 1, 2
RRP = Relative Refractory Period
—> AP may be generated (much larger stimulus)
- phase 3
- keep conduction unidirectional and prevent
overstimulation

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7
Q

What are the 2 main differences between the nodal cell and cardiomyocyte action potential profiles?

A
  1. Phases - nodal —> 3 (0, 3, 4)
    - cardiomyocyte —> 5 (0, 1, 2, 3, 4)
  2. AP duration - nodal —> 2-3ms
    - fast transmission
    - cardiomyocyte —> 200-300ms
    - effective pumping
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8
Q

Which 3 major organ systems control heart activity?

A
  1. CNS
  2. Kidneys
  3. Blood vessels
    - all intertwined
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9
Q

How does the CNS contribute to heart function control?

A
  1. Affects heart rate via ANS (choronotropy)
    • medulla —> cardio-regulatory centre
      —> vasomotor centres
  2. Affects ventricular contraction force via ANS
    (inotropy)
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10
Q

How does the CNS control heart rate?

A

SNS - inc slope of phase 4 (shorter) —> inc HR
PNS - dec slope of phase 4 (longer) —> dec HR

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11
Q

How does the CNS control heart contractility?

A

SNS - inc Ca2+ influx into myofilamnets —> inc
contraction force (inotropy)

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12
Q

What is the path of parasympathetic stimulation of the heart?

A
  1. Pre-ganglionic —> post-ganglionic
    • cardioregulatory centre —> cranial or sacral part
      of spinal cord —> ganglia
    • ACh via nACh-receptors (nicotinic)
  2. Post-ganglionic —> SA node
    • ACh via M2-receptors (muscarinic)
    • Gi receptor —> inhibits adylyl cyclase —> dec ATP
      to cAMP —> dec PKA activity
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13
Q

What is the path of sympathetic stimulation of the heart?

A
  1. Pre-ganglionic —> post-ganglionic
    • cardioregulatory centre —> thoracic or lumbar
      part of spinal cord —> sympathetic trunk
    • ACh to nACh-receptors (nicotinic)
  2. Post-ganglionic —> SA node
    • NA to B1-receptors (adrenergic)
    • Gs receptor —> stimulates adylyl cyclase —> inc
      ATP to cAMP —> inc PKA activity
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14
Q

What is the vasomotor centre?

A

Centre in brain medulla and lower third of pons —> co-ordinates regulation of blood pressure:

  • 3 areas —> vasocontrictor area
    —> vasodilator area
    —> cardio-regulatory inhibitory area
  • stimulation - via higher centres of brain
    (eg. hypothalamus)
  • effects - main —> vasocontriction/dilation
    - via spinal cord neves to most blood
    vessels
    - lateral portions —> heart rate
    —> contractility
    - medial portions —> dec heart rate
    - via vagus nerve
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15
Q

What happens if the sympathetic vs parasymthetic nerves of the heart are cut?

A

Sympathetic —> HR dec
- HR still above when parasympathetic
nerves stimulated —> suggests innate
sympathetic mechanisms
Parasympthatic —> HR inc
- HR still above when sympathetic
nerves stimulated —> suggests
innate parasympathetic mechanisms

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16
Q

How do the kidneys contribute to heart function control? (2)

A
  1. Blood volume - via Na+ excretion
  2. Blood pressure - via renin secretion
17
Q

How does the renal system control blood volume?

A

SNS - stimulates renal afferent arterioles
- NA to α1-adrenoreceptors
—> dec glomerular filtration + inc aldosterone
secretion —> dec Na+ excreted —> dec water
excreted —> inc blood volume
- low blood volume detected by venous volume
receptors

18
Q

How does the renal system control blood pressure?

A

SNS - stimulates juxtaglomerular cells of arterioles
- NA to β1-adrenoreceptors
—> inc renin secretion —> inc angiotensin-II
production —> inc vasoconstriction —> inc BP
- blood pressure detected by arterial baroreceptors

19
Q

How do blood vessels contribute to heart function control?

A
  1. Blood volume via cardiopulmonary circuit
  2. Blood pressure via arterial circuit
20
Q

What are the 2 circuits affecting blood vessels?

A
  1. Cardiopulmonary circuit —> blood volume
    • involves large pulmonary vessels —> have volume
      sensors
  2. Arterial circuit —> blood pressure
    • involves aortic arch, carotid sinus, afferent renal
      arterioles —> have pressure sensors
21
Q

How does the cardiopulmonary circuit control blood volume?

A

Low blood volume:
1. Dec filling of atria and large pulmonary vessels
(cardiopulmonary circuit)
2. Volume sensors send signals via glossopharyngeal
and vagus nerves
3. Dec baroreceptor firing —> inc SNS activity

High blood volume:
1. Distension (stretch) of atria and large pulmonary
vessels (cardiopulmonary circuit)
2. Volume sensors send signals via glossopharyngeal
and vagus nerves
3. Inc baroreceptor firing —> dec SNS activity

22
Q

How does the arterial circuit control blood pressure?

A

Low blood pressure:
1. Low pressure in aortic arch, carotid sinus and
afferent renal arterioles (atrial circuit)
2. Pressures send signals via glossopharyngeal and
vagus nerves
3. Dec baroreceptor firing —> inc SNS activity

High blood pressure:
1. High pressure in aortic arch, carotid sinus and
afferent renal arterioles (atrial circuit)
2. Pressures send signals via glossopharyngeal and
vagus nerves
3. Inc baroreceptor firing —> dec SNS activity

23
Q

What is central venous pressure?

A

Mean pressure in right atrium
- blood flow back to heart —> used to determine
stroke volume

24
Q

What are the 2 effects of venous constriction?

A
  1. Dec compliance —> more rigid
  2. Inc venous return
25
Q

What are the 2 effects of arterial constriction?

A
  1. Inc blood flow to downstream organs —> change
    pattern of blood flow to organs
  2. Inc MAP
26
Q

Which 4 factors increase venous return?

A
  1. Inc blood volume
  2. Inc SNS activation of veins
  3. Inc skeletal muscle pump
  4. Inc respiratory movements
    —> inc venous pressure —> inc venous return —> inc
    atrial pressure
27
Q

What is the resting distribution of blood around the circulatory system? (5)

A
  1. Heart —> 7%
  2. Pulmonary circulation —> 9%
  3. Arteries —> 15%
  4. Arterioles and capillaries —> 5% (least)
  5. Veins and venules —> 64% (most)
    - v. low pressure —> store of
    most blood
28
Q

What are the 4 local mechanisms regulating blood flow?

A

Reflexive regulation of local blood flow in organs via mediators released by vascular endothelial cells

Vasodilators —> vascular smooth muscle relaxation
1. Nitric oxide
2. Prostacyclin - also anti-platelet and anticoagulant

Vasoconstrictors —> vascular smooth muscle
contraction
3. Thromboxane A2 - also from platelets
4. Endothelins - from endothelial cell nucleus

29
Q

What are the 5 systemic mechanisms regulating blood flow?

A

Regulation of systemic blood flow via ANS and hormones

Vasodilators —> vascular smooth muscle relaxation
1. Kinins —> stimulate NO synthesis in endothelium
2. Atrial natriuretic peptide —> from atrium

Vasoconstrictors —> vascular smooth muscle
contraction
3. ADH (pituitary gland) —> binds to V1 receptors
4. NA/adrenaline (adrenal gland)
5. Angiotensin II —> renin-angiotenisin-aldosterone
axis
—> stimulates ADH secretion

2.6 BRS Cardiovascular & Respiratory (15 decks)

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