Control of Heart Function Flashcards
1
Q
What three categories can the main anatomical components of the heart be categorized into?
A
- Muscle cells - cardiomyocytes
- Specialised electrical cells
- Vessels
2
Q
Which cell type in the heart is most prominent in controlling heart function?
A
Electric cells
3
Q
What is the pacemaker of the heart?
A
The Sinoatrial Node
4
Q
What limits does the SAN work to keep the heart rate between?
A
60-100 bpm
5
Q
Where is the SAN found?
A
At the junction of the cristae terminalis, upper wall of right atrium and opening of superior vena cava
6
Q
What is the name given to the tracts between the SAN and the AV Node?
A
Internodal tracts
7
Q
What is the tract which runs down the intraventricular septum?
A
Bundle of His
8
Q
What are the fibres which project upwards around the ventricles from the apex of the heart?
A
The Purknje Fibres
9
Q
Where is the AVN found?
A
At the triangle of Koch at the base of the right atrium
10
Q
What are purkinje fibres?
A
Specialised conducting fibres
11
Q
Does the AVN have pacemaker activity?
A
Yes - slow calcium mediated action potentials
12
Q
What are the three main souces of control of the heart?
A
The kidneys, the central nervous system and the blood vessels
13
Q
Which three phases does a nodal action potential have?
A
0, 3 and 4
14
Q
What is phase 0?
A
The upstroke phase
15
Q
What is Phase 1?
A
early repolarisation
16
Q
What is phase 2?
A
Plateau phase
17
Q
What is phase 3?
A
repolrisation
18
Q
What is phase 4?
A
Resting in cardiac tissue, pre-potential in SAN
19
Q
What causes the upstroke (Phase 0) in nodal cells?
A
The influx of calcium from outside the nodal cell into the nodal cell
20
Q
What causes the repolarisation seen in nodal cells?
A
Due to K+ efflux
21
Q
What causes the pre-potential seen in SAN?
A
The slow flow of Na+ through a funny channel
22
Q
How does the length of a cardiac muscle action potential differ from a nerve action potential?
A
Cardiac muscle action potential is much longer - 200-300ms compared with 2-3ms
23
Q
What does the duration of the cardiac muscle action potential control?
A
The duration of the contraction of the heart
24
Q
What type of contraction is required to produce an effective pump?
A
Long and slow contraction
25
How may phases does the Cardiac Muscle action potential have?
5
26
What are the 5 phases of the cardiac muscle action potential?
```
Phase 0 - Upstroke
Phase 1 - Early Repolarisation
Phase 2 - Plateau
Phase 3 - Repolarisation
Phase 4 - Resting Membrane potential
```
27
What is meant by the absolute refractory period?
The period in which no Action Potential can be initiated regardless of stimulus intensity - this limits the rate at which the heart can beat at
28
What is the relative refractory period?
Period of time after the absolute refractory period in which the heart can elicit another action potential if a large enough stimuli is provided
29
Why is the plateau phase of the cardiac muscle cell action potential so important?
L type Ca2+ Channels open slowly resulting in Ca2+ influx, which maintains the cell at the level of depolarisation - this is essential for generating a large force of contraction
30
What triggers the repolarisation phase in cardiac muscle cells?
The efflux of K+ from the cell
31
What happens when the Cardiac muscle has been sufficiently repolarised?
The K+ channels close, returning the muscle cell to resting membrane potential
32
Why is Ca2+ influx essential for contraction?
heart muscle contracts through Ca2+ enduced Ca2+ release - this means Ca2+ is needed for the release of Ca2+ from the sarcoplasmic reticulum which then binds to troponin on muscle to shorten the fibres and contract it
33
Which ion is the upstroke more reliant on?
Na+
34
What does the autonomic nervous system that controls the heart comprise of?
The cardio-regulatory center and the vasomotor centers in the medulla
35
What nerve is responsible for the parasympathetic changes which are seen in the heart (decrease in heart rate)
Vagus nerve
36
What happens to the slope of Phase 4 (Pre-Potential) of the SAN Action potential during the parasympathetic response?
Decreases the slope
37
Which nerves are involved in the sympathetic control of the heart to increase heart rate?
Cardiac nerves from the lower cervical and thoracic ganglia
38
What affect does the sympathetic response have on the slope of Phase 4 in the sympathetic nervous system?
It increases the slope
39
What length are parasympathetic pre-ganglionic fibres?
Long
40
What length are parasympathetic post-ganglionic fibres?
Short
41
What length are sympathetic post-ganglionic fibres?
Long
42
What length are sympathetic pre-ganglionic fibres?
Short
43
What NT is used at both pre and post-ganglionic synapses in parasympathetic?
ACh
44
What NT is used at sympathetic pre-ganglionic synpases?
ACh
45
What NT is used at sympathetic post-ganglionic synpases?
Noradrenaline
46
What receptors are used at both sympathetic and parasympathetic pre-ganglionic synapses?
nicotinic receptors
47
What receptors are found at parasympathetic post-ganglionic synpases?
muscarinic receptors
48
What receptors are found at sympathetic post-ganglionic synapses?
Adrenergic receptors
49
What does the parasympathetic system control?
Heart rate
50
What does the sympathetic system control?
Circulation
51
Which receptors found in the heart are responsible for an increase in heart rate?
Beta 1 and Beta 2 Receptors
52
What type of receptors are Beta1 and Beta2?
They are adrenoreceptors
53
What is the the result of an increase in chronotrophy?
HR Increases
54
What is the the result of an increase in lusitrophy?
The rate at which the myocyte relaxes increases
55
What is the the result of an increase in ionotrophy?
Contractility increases
56
What is the the result of an increase in dromotrophy?
Conduction velocity increases
57
What are examples of adrenergic agonists?
Noradrenaine and the circulating hormone epinephrine
58
What receptors in the heart do parasympathetic neurotransmitters stimulate?
Muscarinic receptors
59
Why do beta receptors result in an increase in chronotropy, dromotropy, inotropy and lusitropy?
The activation of beta receptors results in the stimulation of secondary messenger systems - stimulated cAMP to make protein kinase A
60
Where is the vasomotor system located?
Located bilaterally in the reticular substance of medulla and lower third of pons
61
What three areas is the vasomotor system composed of?
The Pressor Area - vasoconstrictor
The Depressor Area - vasodilator
The Cardio-regulatory inhibitory area
62
What does the lateral portion of the vasomotor center control?
Controls heart activity by influencing heart rate and contractility
63
What does the medial portion of the vasomotor center control?
Transmits parasympathetic signals via the Vagus nerve to the heart that tend to decrease heart rate
64
Where does the vasomotor center transmit impulses to?
The heart and almost all the blood vessels - through the spinal cord
65
what is the network of nerves which supplies the heart called?
The cardiac plexus
66
What does the right vagus nerve primarily innervate?
The Sinoatrial Node
67
what does the left vagus nerve primarily innervate?
The AV Node
68
What happens to Beta 1 Receptors in the heart during heart failure?
They become downregulated
69
What is the result of NA binding to alpha 1 adrenoreceptors found on myocytes?
Produces small increases in inotrophy - increase in contractility
70
What is the effect of ACh released from the vagus nerve binding to M2 receptors in the heart - especially SAN and AVN?
Decrease in chronotropy and dromotropy in the heart
Decrease in inotropy and lusitropy in the atria
71
What effect does sympathetic innervation on the kidney have on GFR?
Reduces glomerular filtration
72
What affect does sympathetic innervation on the kidneys have on blood volume?
Less GFR, Means Less Na+ Excreted, so more in blood, therefore more water in blood therefore higher blood volume
73
What detects the change in blood volume?
Venous volume receptors in the heart
74
How does a higher blood volume lead to higher blood pressure?
High blood volume = High renin = More Angiotensinogen = More Angiotensin II = More Aldosterone = Vasoconstriction = increase in blood pressure
75
Activation of what receptor causes Increase Renin secretion?
Activation of the Beta-1 Adrenoreceptors
76
How does the GFR decrease with sympathetic innervation?
Sympathetic nerves stimulate the alpha1 Adrenoreceptors via NA release which causes vasoconstriction, and therefore less GFR and Less Na+ excretion
77
What effect does an increase in blood volume have on inotropy?
It will increase inotrophy
78
What do baroreceptors detect?
Changes in blood pressure and volum
79
Blood volume changes is due to what system?
Decrease GFR due to sympathetic stimulation
80
Blood pressure changes is due to what system?
The RAAS
81
When baroreceptors firing rate reduces, what happens to SNS activity?
It increases to increase heart rate
82
When baroreceptors firing rate increases, what happens to SNS activity?
Decreases, so reduction in chronotropy
83
What nerves do volume sensors send signals through?
glossopharyngeal and vagus
84
What nerves do pressure sensors send signals through?
Glossopharyngeal and vagus
85
Where are pressure sensors found that change baroreceptor firing?
In the arterial circuit
86
Where are volume receptors found?
In large pulmonary vessels
87
What five factors effect venous volume distribution
Peripheral venous tone, gravity, skeletal muscle pump and breathing
88
What is meant by the central venous pressure?
The mean pressure of the right atrium - determines how much blood flows back to the heart
89
Which area of the cardiovascular system contain the biggest reservoir of blood
Veins and venules
90
What does constriction in veins determine?
Compliance (reduced) and venous return (increased)
91
Which physiological change will cause an immediate increase in baroreceptor firing
Increased central venous pressure
92
What does constriction in arterioles determine?
Blood flow to downstream organs
Mean Arterial Pressure
Pattern of Flow to Organs
93
What are two endothelium derived vasodilators?
nitric oxide and prostacylin
94
What are two endothelium derived vasoconstrictors?
Endothelins and thromboxane A2
95
How does ADH cause vasoconstriction?
Binds to V1 receptors on smooth muscle
96
What is the most potent vasoconstrictor?
Angiotensin II
