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Cardiovascular and Respiratory > Control of Heart function > Flashcards

Control of Heart function Flashcards

1
Q

What anatomical components can the heart be categorised into?

A

Muscle cells = cardio-myocytes
Specialised electrical cells
Vessels

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2
Q

What are Cardio Myocytes?

A

Heart muscle cells:

can contract and relax in response to electrical stimuli. Essential for pumping blood around the body

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3
Q

What are Specialised Electrical cells?

A

Cells that create spontaneous currents and those that transmit currents exist within the heart. Essential for regulating contraction of the cardio-myocytes

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4
Q

What are Vessels used for?

A

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 cells are most prominent in controlling heart function?

A

Electrical Cells

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6
Q

What are the nodes of the heart?

A

SinoAtrial (SA)

AtrioVentrocular (AV)

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7
Q

What is the pacemaker of the heart and where is it found?

A

SA node
(pacemaker - beats at 60-100 bpm)
located in the Junction of Cristae terminalis; upper wall of right atrium & opening of superior vena cava

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8
Q

What else has pacemaker potential?

A

AtrioVentricular node

- has slow calcium mediated action potential

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9
Q

Where is the AV node located?

A

Triangle of Koch at base of right atrium * diagram

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10
Q

What connects the SAN to the AVN ?

A

Internodal tracts = specialised myocytes

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11
Q

What is the pathway of the bundle of his (tract)

A

Atria -> interventricular septum -> bundles branches -> purkinje fibres

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12
Q

What propagates the electrical current along the ventricles?

A

Purkinje Fibres. They are specialised conducting fibres

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13
Q

What are the Nodal cell action potential phases?

A

0,3,4
membrane potential between minus 40 and minus 60mV.
Phase 4: is going from -40 to -60 = Pre-potential
Depolarisation to +20mV = Phase 0 (upstroke)
Phase 3: Repolarisation , back down to minus 60mV

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14
Q

What is te depolarisation in a nodal cell due to?

A

calcium influx (Ca2+ into the nodal cell)

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15
Q

What is the repolarisation in a nodal cell due to?

A

Potassium efflux

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16
Q

What is the resting potential of a nodal cell?

A

they don’t have one but instead have a prepotential due to Na+ influx through a ‘funny’ channel

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17
Q

Does the cardiac muscle follow the same action potential shape as the nodes? why/why not?

A

no, all parts = slightly diff bc of different ion currents flowing and different ion channel expression in cell membrane

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18
Q

Why is Cardiac muscle action potential long?

A

Cardiac Ap = 200-300ms which is 100x longer than nerves
Long, slow contractions needed to produce an effective pump. (the duration of AP controls the duration of heart contraction)

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19
Q

What is the resting membrane potential of the cardiac muscle cells?

A

-90mV

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20
Q

Phases of Cardiac muscle AP

A

Phase 0 = Upstoke - depolarisation phase from -90mv to +20mV due to Na+ influx
Phase 1 = Early repolarisation due to a bit of K+ efflux
Phase 2= plateau due to Ca2+ influx (maintains a level of depolarisation
Phase 3= Repolarisation due to K+ efflux
Phase 4 = Resting membrane potential

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21
Q

How long does it take for a full repolarisation of cardiac muscles?

A

270ms

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22
Q

What is the Absolute Refractory Period (ARP)?

A

Time during which no AP can be generated regardless of stimulus intensity.
bc don’t want 1 whilst ur in the middle of another

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23
Q

What limits the maximum rate at which the heart can beat at?

A

The ARP

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24
Q

What is the Relative Refractory period (RRP)?

A

Period after an ARP where an AP can be elicited but only with a larger stimulus. They tend not to occur but can if stimulus is strong enough

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25
Q

What is involved in the exogenous regulation of the heart?

A
  • CNS
  • Kidney
  • Vessels
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26
Q

What is the role of the brain/cns in the activity of the heart?

A

can effect immediate changes through nerve activity or slower changes through hormonal activity.
it also impacts other systems which subsequently affect the heart

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27
Q

Which nervous system is involved in the control of the heart? (autonomic or somatic)

A

Autonomic which consist of 2 components = Cardio-regulatory centre & vasomotor centres in medulla

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28
Q

Path of the parasympathetic nerve?

A

Leaves from medulla and goes to the heart via the vagus nerve

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29
Q

What does the parasympathetic nerve do when its activated?

A

Decreases heart rate by decreasing the slope of phase 4 in the nodal cell : affects prepotential
mostly SAN but can regulate AVN

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30
Q

What does the sympathetic nerve do when its activated?

A

Increases heart rate = positive chronotropy
increases slope of nodal cell phase 4
decreases times of ap.
mostly SAN but can regulate AVN

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31
Q

What increases the force of contraction in the heart (part of sympathetic ns)

A

calcium dynamics

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32
Q

Where do parasympathetic nerves arise from?

A

Cranial & Sacral part of the spinal cord

imp for controlling heart rate

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33
Q

Structure & neurotransmitter of the ps nerves?

A 
Preganglionic fibres (closer to brain)  - release acetyl choline and have nictonic receptors
post ganglionic fibre also releases ACh but have muscarinic receptors
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34
Q

Where do the sympathetic nerves arise from?

A

thoracic & lumbar vertebrae of the spinal cord

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35
Q

Neurotransmitters for the sympathetic nerve?

A

Pre-ganglionic fibres use ACh and still have nicotinic receptors
but at most post-ganglionic fibres the nt is usually noradrenaline. but not always

36
Q

What is the sympathetic chain/ganglia?

A

sympathetic nerves synapse here resulting in longer post synaptic fibres
aka paravertebral ganglia

37
Q

Where is the Vasomotor centre loacted?

A

Bilaterally in reticular substance of medulla & lower third of pons

38
Q

What is the Vasomotor centre composed of?

A

Vasoconstrictor/pressor area
Vasodilator/depressor area
Cardio-regulatory inhibitory area

39
Q

What is a pressor response?

A

Results in vasoconstriction

40
Q

What is a depressor response?

A

Results in vasodilation

41
Q

What can have excitatory or inhibitory effects on the VMC?

A

Many higher centres of the brain such as the hypothalamus

42
Q

How do the lateral portions of the VMC control heart activity?

A

by influencing heart rate and contractility

43
Q

How does the medial portion of the VMC control heart activity?

A

Transmits signals via the vagus nerve to the heart which tend to decrease heart rate

44
Q

Which receptors in the heart are acted upon by ACh from parasympathetic nerves?

A

Ach from psn acts on the M2 Muscarinic receptors on the membrane of a sino-atrial nodal cell

45
Q

What is the ps nerve action?

A

Ach acts on M2 muscarinic receptors and viathe G protein (Gi) i inhibits adenylyl cyclase which then prevents conversion of ATP into protein kinase A

46
Q

sympathetic nerve action?

A

Noradrenaline acts on beta 1 receptors in san cell membrane. via a second messenger, it stimulates adenylyl cyclase and increases protein kinase A

47
Q

What happens if you remove parasympathetic or sympathetic nerves from heart and what does this show?

A

ps: heart rate and activvity will go up
removing s: heart rate will go down.

shows there is basal activity - occurs all the time and not just upon stimulation, of both nerves. but basal ps > basal s

48
Q

Which receptor transmits the signal from the pre- to the post-ganglionic nerves in the sympathetic nervous system?

A

nicotinic ACh receptor

These receptors are present at the post-synaptic terminals throughout the autonomic nervous system

49
Q

Does the Kidney have a DIRECT impact on the heart?

A

No, The heart and kidneys share a bi-directional regulatory relationship usually through indirect mechanisms (i.e. the CNS & the blood vessels)

50
Q

What do the kidneys regulate in terms of exogenous regulation of the heart?

A

blood volume and blood pressure

51
Q

Which nerves innervate the kidneys?

A

sympathetic

52
Q

Effect of sympathetic nerves on blood volume

A

increase in sy nerve activity =
decrease in glomerular filtrate and so reduces sodium excretion - leads to increase in blood volume. also do this via aldosterone

53
Q

Effect of sympathetic nerves on blood pressure

A

increased s nerve activity causes an increase in renin secretion which increases angiotensin II production:
this causes vasoconstriction which increases BP.

54
Q

Angiotensin-II’s role in blood volume?

A

Angiotensin-II also produces Aldosterone

which has a role in blood volume

55
Q

What detects blood pressure?

A

Arterial baroreceptors

56
Q

Which vessels in the kidney do the sympathetic nerve fibres innervate?

A

afferent & efferent arterioles of the glomerulus (& nephron tubule cells)

57
Q

How do sympathetic nerve fibres cause vasoconstriction in the afferent arteriole?

A

Vasoconstriction:
Noradrenaline released which acts on alpha-1-adrenoreceptors which causes vasoconstriction.

vasoconstriction cause a reduction in glomerular filtrate and sodium filtered which increases blood vol

58
Q

Where does Noradrenaline act in the afferent arterioles of the kidney?

A

On alpha 1-adrenoreceptorsq

59
Q

Where is renin synthesised?

A

juxtaglomerular cells - also stored and released from here

60
Q

How do sympathetic nerves cause an increase in renin secretion?

A

act of beta 1- adrenoreceptors in jxg cells which leads to renin secretion. this will increase aldosterone section so increase blood volume

61
Q

What effect will activation of renal arteriole alpha-1 receptor eventually have on the heart?

A 
Reduced chronotropy (reduced heart rate)  & increased inotropy (increased force) :
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)
62
Q

What relationship do the heart and blood vessels share?

A

the heart and the blood vessels share a bi-directional regulatory relationship usually through indirect mechanisms (i.e. the CNS & the kidneys)

63
Q

What do the blood vessels regulate in terms of exogenous regulation of the heart?

A

blood pressure & blood volume

64
Q

What are cardiopulmonary vessels?

A

Large vessels that are volume sensors(also atria & right ventricle)
which form the cardiopulomanary circuit

65
Q

What happens when we get a decrease in the filling of the heart due to bv ?
(cardiopulmonary circuit)

A

reduction in baroreceptor firing and increase in sympathetic nerve activity which increases heart rate (vagus nerve?????)

66
Q

What happens when we have distention? (heart seems full)

cardiopulmonary circuit

A

Increase in baroreceptor firing and a decrease in SNS activity which will decrease heart rate

67
Q

What controls how much blood comes back to the heart?

cardiopulmonary circuit

A

blood vessels and the kidney

68
Q

What is the other circuit which controls the heart? (other than cardiopulmonary)

A

Arterial which includes aortic arch, carotid sinus & afferent arterioles of kidney

69
Q

what nerves do the large pulmonary vessels send signals through?

A

glossopharyngeal & vagus nerves

70
Q

What nerves do the arteries in the arterial circuit send signals through?

A

glossopharyngeal & vagus nerves.

71
Q

What type of sensors are the arteries in the arterial circuit?

A

pressure

72
Q

a decrease in pressure leads to a (a) in baroreceptor firing and an increase in (b) activity

A 
a = decrease
b= SNS

(whatever happens to pressure happens to barorecep and opposite to SNS) (increases heart rate)

73
Q

What happens when pressure increases?

A

Increase in pressure:

increase in barorecp firing which decreases SNS activity (slows heart rate)

74
Q

What are the circulations of the heart?

A

Pulmonary & Venous

75
Q

How much blood is in the veins and venules and what is this volume affected by?

A

61%

distribution affected by peripheral venous tone, gravity, skeletal muscle pump & breathing

76
Q

What is central venous pressure?

A

mean pressure in the right atrium

77
Q

What determines the amount of blood flowing back to the heart?

A

Central venous pressure

- determines filling pressure and distension of heart

78
Q

What law can central venous pressure relate to ?

A

Starling’s:
- amount of blood flowing back to the heart determines stroke volume.
> pressure leads to a > volume

79
Q

What does constriction do in veins?

A

Reduces compliance & increases venous return

80
Q

How much blood is there in the arteries?

A

11% only BUT this blood is under higher pressure

81
Q

What does constriction determine in arteries?

A
  1. blood flow to the downstream organs
  2. Mean arterial blood pressure
  3. The pattern of blood flow to the organs
82
Q

How much blood is in

a) the pulmonary circulation
b) arterioles and capillaries
c) heart

A

a) 17%
b) 7%
c) 9%

83
Q

Local Mechanisms for regulating blood flow

A
  • Intrinsic to smooth muscle / closely associated

- important for reflex local blood flow within an organ

84
Q

Which endothelium-derived mediators impacting the vein & arteries cause vasodilation?

A 
Nitric Oxide (NO) - potent vasodilator, which diffuses into vascular smooth muscle cells
Prostacyclin - vasodilator that has antiplatelet & anticoagulanteffects too
85
Q

Which endothelium-derived mediators impacting the vein & arteries cause vasoconstriction?

A

Thromboxane A2 - also heavily synthesised in platelets

Endothelins (ET) - generated from nuscleus of endothelial cells

86
Q

What are systemic mechanism for regulating blood flow?

A

Extrinsic to smooth muscle

include autonomic nervous system & circulating hormones

87
Q

Examples of systemic mechanisms?

A

non-endothelium dervided mediators:
- Kinins w vasodilator effects: bind to endothelial cells receptors & stimulate NO synthesis
Atrial natiuretic peptide - vasodilator
ADH= vasoconstrictor: secreted from pituitary and binds to V1 receptors on smooth muscles to cause vc.
Norad/adrenaline = vasoconstrictor
angiontensin II = potent vasoconstrictor

Cardiovascular and Respiratory (5 decks)

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