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Cardiovascular and Respiratory > Control of Heart function > Flashcards

Control of Heart function Flashcards

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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
What is involved in the exogenous regulation of the heart?
- CNS - Kidney - Vessels
26
What is the role of the brain/cns in the activity of the heart?
can effect immediate changes through nerve activity or slower changes through hormonal activity. it also impacts other systems which subsequently affect the heart
27
Which nervous system is involved in the control of the heart? (autonomic or somatic)
Autonomic which consist of 2 components = Cardio-regulatory centre & vasomotor centres in medulla
28
Path of the parasympathetic nerve?
Leaves from medulla and goes to the heart via the vagus nerve
29
What does the parasympathetic nerve do when its activated?
Decreases heart rate by decreasing the slope of phase 4 in the nodal cell : affects prepotential mostly SAN but can regulate AVN
30
What does the sympathetic nerve do when its activated?
Increases heart rate = positive chronotropy increases slope of nodal cell phase 4 decreases times of ap. mostly SAN but can regulate AVN
31
What increases the force of contraction in the heart (part of sympathetic ns)
calcium dynamics
32
Where do parasympathetic nerves arise from?
Cranial & Sacral part of the spinal cord | imp for controlling heart rate
33
Structure & neurotransmitter of the ps nerves?
``` Preganglionic fibres (closer to brain) - release acetyl choline and have nictonic receptors post ganglionic fibre also releases ACh but have muscarinic receptors ```
34
Where do the sympathetic nerves arise from?
thoracic & lumbar vertebrae of the spinal cord
35
Neurotransmitters for the sympathetic nerve?
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
What is the sympathetic chain/ganglia?
sympathetic nerves synapse here resulting in longer post synaptic fibres aka paravertebral ganglia
37
Where is the Vasomotor centre loacted?
Bilaterally in reticular substance of medulla & lower third of pons
38
What is the Vasomotor centre composed of?
Vasoconstrictor/pressor area Vasodilator/depressor area Cardio-regulatory inhibitory area
39
What is a pressor response?
Results in vasoconstriction
40
What is a depressor response?
Results in vasodilation
41
What can have excitatory or inhibitory effects on the VMC?
Many higher centres of the brain such as the hypothalamus
42
How do the lateral portions of the VMC control heart activity?
by influencing heart rate and contractility
43
How does the medial portion of the VMC control heart activity?
Transmits signals via the vagus nerve to the heart which tend to decrease heart rate
44
Which receptors in the heart are acted upon by ACh from parasympathetic nerves?
Ach from psn acts on the M2 Muscarinic receptors on the membrane of a sino-atrial nodal cell
45
What is the ps nerve action?
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
sympathetic nerve action?
Noradrenaline acts on beta 1 receptors in san cell membrane. via a second messenger, it stimulates adenylyl cyclase and increases protein kinase A
47
What happens if you remove parasympathetic or sympathetic nerves from heart and what does this show?
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
Which receptor transmits the signal from the pre- to the post-ganglionic nerves in the sympathetic nervous system?
nicotinic ACh receptor These receptors are present at the post-synaptic terminals throughout the autonomic nervous system
49
Does the Kidney have a DIRECT impact on the heart?
No, The heart and kidneys share a bi-directional regulatory relationship usually through indirect mechanisms (i.e. the CNS & the blood vessels)
50
What do the kidneys regulate in terms of exogenous regulation of the heart?
blood volume and blood pressure
51
Which nerves innervate the kidneys?
sympathetic
52
Effect of sympathetic nerves on blood volume
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
Effect of sympathetic nerves on blood pressure
increased s nerve activity causes an increase in renin secretion which increases angiotensin II production: this causes vasoconstriction which increases BP.
54
Angiotensin-II's role in blood volume?
Angiotensin-II also produces Aldosterone | which has a role in blood volume
55
What detects blood pressure?
Arterial baroreceptors
56
Which vessels in the kidney do the sympathetic nerve fibres innervate?
afferent & efferent arterioles of the glomerulus (& nephron tubule cells)
57
How do sympathetic nerve fibres cause vasoconstriction in the afferent arteriole?
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
Where does Noradrenaline act in the afferent arterioles of the kidney?
On alpha 1-adrenoreceptorsq
59
Where is renin synthesised?
juxtaglomerular cells - also stored and released from here
60
How do sympathetic nerves cause an increase in renin secretion?
act of beta 1- adrenoreceptors in jxg cells which leads to renin secretion. this will increase aldosterone section so increase blood volume
61
What effect will activation of renal arteriole alpha-1 receptor eventually have on the heart?
``` 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
What relationship do the heart and blood vessels share?
the heart and the blood vessels share a bi-directional regulatory relationship usually through indirect mechanisms (i.e. the CNS & the kidneys)
63
What do the blood vessels regulate in terms of exogenous regulation of the heart?
blood pressure & blood volume
64
What are cardiopulmonary vessels?
Large vessels that are volume sensors(also atria & right ventricle) which form the cardiopulomanary circuit
65
What happens when we get a decrease in the filling of the heart due to bv ? (cardiopulmonary circuit)
reduction in baroreceptor firing and increase in sympathetic nerve activity which increases heart rate (vagus nerve?????)
66
What happens when we have distention? (heart seems full) | cardiopulmonary circuit
Increase in baroreceptor firing and a decrease in SNS activity which will decrease heart rate
67
What controls how much blood comes back to the heart? | cardiopulmonary circuit
blood vessels and the kidney
68
What is the other circuit which controls the heart? (other than cardiopulmonary)
Arterial which includes aortic arch, carotid sinus & afferent arterioles of kidney
69
what nerves do the large pulmonary vessels send signals through?
glossopharyngeal & vagus nerves
70
What nerves do the arteries in the arterial circuit send signals through?
glossopharyngeal & vagus nerves.
71
What type of sensors are the arteries in the arterial circuit?
pressure
72
a decrease in pressure leads to a (a) in baroreceptor firing and an increase in (b) activity
``` a = decrease b= SNS ``` (whatever happens to pressure happens to barorecep and opposite to SNS) (increases heart rate)
73
What happens when pressure increases?
Increase in pressure: | increase in barorecp firing which decreases SNS activity (slows heart rate)
74
What are the circulations of the heart?
Pulmonary & Venous
75
How much blood is in the veins and venules and what is this volume affected by?
61% | distribution affected by peripheral venous tone, gravity, skeletal muscle pump & breathing
76
What is central venous pressure?
mean pressure in the right atrium
77
What determines the amount of blood flowing back to the heart?
Central venous pressure | - determines filling pressure and distension of heart
78
What law can central venous pressure relate to ?
Starling's: - amount of blood flowing back to the heart determines stroke volume. > pressure leads to a > volume
79
What does constriction do in veins?
Reduces compliance & increases venous return
80
How much blood is there in the arteries?
11% only BUT this blood is under higher pressure
81
What does constriction determine in arteries?
1. blood flow to the downstream organs 2. Mean arterial blood pressure 3. The pattern of blood flow to the organs
82
How much blood is in a) the pulmonary circulation b) arterioles and capillaries c) heart
a) 17% b) 7% c) 9%
83
Local Mechanisms for regulating blood flow
- Intrinsic to smooth muscle / closely associated | - important for reflex local blood flow within an organ
84
Which endothelium-derived mediators impacting the vein & arteries cause vasodilation?
``` Nitric Oxide (NO) - potent vasodilator, which diffuses into vascular smooth muscle cells Prostacyclin - vasodilator that has antiplatelet & anticoagulanteffects too ```
85
Which endothelium-derived mediators impacting the vein & arteries cause vasoconstriction?
Thromboxane A2 - also heavily synthesised in platelets | Endothelins (ET) - generated from nuscleus of endothelial cells
86
What are systemic mechanism for regulating blood flow?
Extrinsic to smooth muscle | include autonomic nervous system & circulating hormones
87
Examples of systemic mechanisms?
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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