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Cardiology > Control of Heart Function > Flashcards

Control of Heart Function Flashcards

1
Q

What components of the autonomic nervous system are found in the medulla?

A

Cardio-Regulatory centre and vasomotor centres

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2
Q

What does the parasympathetic nervous system do to the heart?

A

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

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3
Q

What does the sympathetic nervous system do to the heart?

A

‘fight or flight’
Increases HR (chronotropy) – increases the slope of phase
Increases force of contraction (inotropy) – increases Ca2+ dynamics
Only active in certain situations

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4
Q

What does the sympathetic nervous system do to the renal system?

A

Increases activity
Decreases glomerular filtration
Decreases Na+ excretion and increases blood volume
Increases blood pressure

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5
Q

How is blood volume detected?

A

Venous volume receptors

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6
Q

What else does the sympathetic nervous system do to the renal system?

A

Increases renin secretion

Increases angiotensin II production

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7
Q

What does angiotensin do?

A

Potent vasoconstrictor

Increases blood pressure

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8
Q

How is blood pressure detected?

A

Arterial baroreceptor

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9
Q

Where are volume sensors in the heart?

A

Large pulmonary vessels
Atria
Right ventricle

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10
Q

How can volume sensors in the cardiopulmonary circuit control the heart?

A

send signals though glossopharyngeal & vagus nerves
Decrease in filling Decreases baroreceptor firing
Activated sympathetic nerve (SNS) activity
Distention leads to increased baroreceptor firing
Reduces SNS activity

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11
Q

How can the arterial circuit control the heart?

A

Pressure sensors: send signals though glossopharyngeal & vagus nerves
Decrease in pressure  Decreased baroreceptor firing Increased SNS activity
Increase in pressure
Increased baroreceptor firing
Decreased SNS activity

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12
Q

What comprise the autonomic nervous system?

A

Parasympathetic

Sympathetic

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13
Q

What are the main features of the parasympathetic nervous system?

A

rest and digest’
Pre-ganglionic fibres use ACh as neurotransmitter
PNS post ganglionic NT = ACh
PNS is important for controlling the heart rate

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14
Q

What are the main features of the sympathetic nervous system?

A

‘fight or flight’
Pre-ganglionic fibres use ACh as their neurotransmitter
SNS post ganglionic NT = NA
SNS is important for controlling the circulation

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15
Q

Where is the vasomotor centre?

A

bilaterally in reticular substance of medulla & lower third of pons

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16
Q

What is the vasomotor centre comprised of?

A

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

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17
Q

Where does the VMC transmit impulses?

A

Transmits impulses distally through spinal cord to almost all blood vessels

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18
Q

What does the VMC do?

A

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

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

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19
Q

How is the VMC controlled>

A

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

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20
Q

How is the sympathetic innervation in the heart involved in control?

A

Increases activity of SAN
Cyclic AMP activated by beta-1 receptors
Regulates different ion channels that control heart rate and force of contraction

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21
Q

How is the parasympathetic innervation in the heart involved in control?

A

Decreases activity of SAN
Cyclic AMP activated by beta-1 receptors
Regulates different ion channels that control heart rate and force of contraction

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22
Q

How do these systems work under normal resting conditions?

A

Tonic underlying activity of both sympathetic and parasympathetic
Parasympathetic has more activity in resting conditions
If all nerves were cut there would be an overall increase in heart rate

23
Q

How do sympathetic nerves innervate the renal system?

A

Sympathetic nerve fibres innervate afferent & efferent arterioles of the glomerulus (& nephron tubule cells)
More of effect of afferent than efferent arteriole

24
Q

What is the role of afferent arterioles in control of the heart?

A

Primary site of sympathetic activity
Relasese of noradrenaline
alpha 1-adrenoceptor Increased vasoconstriction (more so in the afferent arteriole)
Decrease in glomerular filtration rate
Decreased Na+ filtered
More sodium in body increases blood volume

25
Q

What is the role of juxtaglomerular cells in the control of the heart?

A

Noradrenaline acts on beta-1 receptors
Juxtaglomerular cells are the site of synthesis, storage & release of renin
Increases renin secretion
Increase in angiotensin II
Vasoconstriction increases blood pressure

26
Q

What are the two circulatory systems?

A

Pulmonary

Systemic

27
Q

What is venous volume affected by?

A

peripheral venous tone, gravity, skeletal muscle pump & breathing

28
Q

What does central venous pressure determine?

A

Determines amount of blood flowing back to heart

29
Q

What is central venous pressure?

A

Mean pressure in the right atrium

30
Q

What determines the stroke volume?

A

Amount of blood flowing back to the heart

31
Q

What does vasoconstriction in veins result in?

A

Reduces compliance and venous return

32
Q

What does vasoconstriction in arteries result in?

A

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

33
Q

What are the main vasodilators in the body?

A 
Nitric oxide
Prostacyclin
(Endothelium-derived)
Kinins
ANP
(Non-endothelium derived)
34
Q

What are the main vasoconstrictors in the body?

A 
Thromboxane
Endothelins
(Endothelium-derived)
Vasopressin
Noradrenaline/Adrenaline
Angiotensins
(Non-endothelium derived)
35
Q

B1 receptor activation in renal afferent arterioles will have which initial affect?

A

Secretion of renin

36
Q

What are the main component of the electrical signalling of the heart?

A

SAN
AVN
Bundles of His
Purkinje fibres

37
Q

How does the cardiac action potential differ from the vast majority of nerve cells?

A

cardiac action potential (AP) is very long (200-300 ms vs. 2-3 ms)
Duration of AP controls duration of contraction of heart
Long, slow contraction is required to produce an effective pump

38
Q

How many phases are there of the cardiac AP?

A

AP has 5 phases numbered 0-4

39
Q

What happens in phase 0 +1?

A

0: Depolarisation phase that leads to the initial contraction in the cardiac myocyte
1: Early depolarisation

40
Q

What happens in phase 2?

A

Plateaus

Important in production og prolonged contraction

41
Q

What happens in phase 2?

A

Repolarisation

42
Q

What happens in phase 3?

A

Resting membrane potential

43
Q

What is the ARP?

A

During plateau phase

Absolute refractory period (ARP) = time during which no AP can be initiated regardless of stimulus intensity

44
Q

What is RRP>

A

Relative refractory period (RRP) = period after ARP where an AP can be elicited but only with larger stimulus strength

45
Q

What determines the RMP?

A

K+ efflux

46
Q

What is the upstroke determined by?

A

By large increase in membrane to Na+ permeability

47
Q

What is essential for contraction that occurs in phase 2?

A

Ca2+ influx required to trigger Ca2+ release from intracellular stores

Ca2+ current (ICa) activates rapidly (within a few milliseconds) but the upstroke is more dependent on INa

48
Q

What occurs if phase 3?

A

Gradual activation of K+ currents (K+ moving outward) that balance, then overcome, inward flow of Ca2+

Large K+ current (IK1) that is inactive during the plateau starts to flow once the cells have partially repolarised

IK1 is responsible for fully repolarising the cell

49
Q

How is the RMP re-established?

A

IK1 is large and flows during diastole. It stabilises the resting membrane potential

50
Q

What is different about different parts of the heart?

A

Different parts of the heart have different action potential shapes

Caused by different ion currents flowing and different ion channel expression in cell membrane

51
Q

Describe the phases of SA node AP

A

SA node AP only has phase 0, 3 & 4
No early repolarisation or plateau phase
Resting membrane potential becomes ‘pre-potential’ due to T-type Ca2+ channels & ‘funny’ current (If)

52
Q

What is a T-type Ca2+ channel?

A

Transient

‘quicker’

53
Q

Why do pacemaker cells not have a phase 4?

A

They do not rest for long

Cardiology (16 decks)

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