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BRS 6: Cardiovascular And Respiratory Medicine > 6.14: Control of heart function > Flashcards

6.14: Control of heart function Flashcards

(59 cards)

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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

Study These Flashcards
A

Heart activity by influencing heart rate and contractility

25
What does the medial portion of the VMS transmit signals via and to
Vagus nerve to heart Decrease heart rate
26
What nerves are involved in the renal system
Sympathetic nerves
27
How is an increase in renal activity brought about
Decrease in glomerular filtration Decrease in Na+ excretion Increase in blood volume (aldosterone)
28
What is kidney blood volume detected by
Venous volume receptor
29
How is a decrease in renal activity brought about
Increased renin secretion Increased angiotensin-II production Vasoconstriction Increased blood pressure
30
What receptors is blood pressure in the kidneys detected by
Arterial baroreceptors
31
Where do sympathetic nerve fibres innervate the kidneys
Innervate afferent and efferent arterioles of glomerulus (and nephron tube cells)
32
How does the sympathetic nervous system bring about a response in the kidneys
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
The cardiopulmonary circuit consists of
Large pulmonary vessels
34
How is the cardiopulmonary circuit regulated
Volume sensors (atria, right ventricle) send signals through glossopharyngeal and vagus nerves
35
What does a Decrease in filling of the heart causes (cardiopulmonary circuit)
Decreased baroreceptor firing Increased sympathetic nervous activity
36
Distension of cardiopulmonary circuit leads to
Increased baroreceptor firing Decreased SNS activity
37
The arterial circuit consists of
Aortic arch Carotid sinus Afferent arterioles of kidneys
38
What do the Pressure sensors in the arterial circuit send signals through
Send signals through glossopharyngeal and vagus nerves
39
What does a decrease in pressure in the arterial circuit lead to
Decreased baroreceptor firing Increased SNS activity
40
What does an increase in pressure of the arterial circuit lead to
Increased baroreceptor firing Decreases SNS activity
41
Two circulations of cardiopulmonary system
Systemic Pulmonary
42
What is venous volume distribution affected by
Peripheral venous tone Gravity Skeletal muscle pump Breathing
43
Central venous pressure determines the
Amount of blood flowing back to the heart
44
The amount of blood flowing back to the heart determines
Stroke volume ( using starlings law of the heart)
45
In veins, constriction reduces and increases
Reduces compliance Increases venous return
46
In arterioles, constriction determines
Blood flow to downstream organs Mean arterial blood pressure The pattern of blood flow to organs
47
Why are local mechanisms essential in regulating blood flow
(Intrinsic to smooth muscle) Important for reflex local blood flow regulation within an organ
48
4 endothelium derived mediators include :
Nitric oxide Prostacyclin Thromboxane A2 Endothelins
49
How does Nitric oxide act as a local blood flow mediator
Potent vasodilator Diffuses into vascular smooth muscle cells
50
How does prostacyclin act as a local blood flow mediator
Vasodilator Has antiplatelet and anticoagulant effects
51
How does TXA2 act as a local blood flow mediator
Vasoconstrictor Heavily synthesised in platelets
52
How do endothelins act as a local blood flow mediator
Vasoconstrictors Generated from nucleus of endothelial cells
53
Characteristics of Systemic mechanisms in regulating blood flow
Extrinsic to smooth muscle Include autonomic nervous system and circulating hormones
54
5 non-endothelium derived mediators
Kinins Atrial natriuretic peptide Vasopressin (ADH) Noradrenaline / Adrenaline Angiotensin II
55
How do kinins act as a systemic blood flow mediator
Bind to receptors on endothelial cells and stimulate NO synthesis Vasodilator effects
56
How does ANP act as a systemic blood flow mediator
Secreted from atria in response to stretch Vasodilator effects to reduce BP
57
How does ADH act as a systemic blood flow mediator
Secreted from pituitary gland Binds to V1 receptors on smooth muscle to cause vasoconstriction
58
How do noradrenaline / adrenaline act as a systemic blood flow mediator
Secreted from adrenal gland Vasoconstriction
59
How does angiotensin II act as a systemic blood flow mediator
Potent vasoconstrictor from renin-angiotensin-aldosterone axis Stimulates ADH secretion

BRS 6: Cardiovascular And Respiratory Medicine (12 decks)

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