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Phase 1A
Andrew Hu + Elaine Pang
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• The tiniest amount of heart anatomy• Activation and Contraction• Cardiac Cycle• Control of MAP
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Aims and Objectives
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Anatomy
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Anatomy
• Called the pacemaker• P-wave• Located in the right atrium• Transmits across both atria• Transmission goes to AV node
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Sino-atrial node
• Specialised myocytes• Base of the right atrium• Transmit impulse deliberately
slowly (0.1s)• Purely there to allow for atrial
contraction
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Atrioventricular node
• Impulse then travels down the IVS– Initially as AV bundle (His) – Splits into RBB and LBB
• Splits into the Purkinje fibres at base of ventricles
• Spreads upwards and outwards– Contract from base– 20-40 bpm
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Atrioventricular node
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Actin and MyosinTroponin C – calcium binds to cause conformational change in Troponin ITroponin T – Binds to tropomyosin forming a tropomyosin troponin complexTroponin I – binds to actin, to hold the tropomyosin – troponin complexes in place
1. Excitation2. L Type Ca channels in T tubules open causing
influx of Ca3. Ca binds to sarcoplasmic opening lateral sacs
releasing more Ca4. Ca binds to TnC moving tropomyosin5. Allows energized myelin to bind to actin6. Repolarization and Ca reuptaken
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Contraction
Energised cross-bridge binds to actin
Cross-bridge moves
ATP binds to myosin → cross bridge detaches
Hydrolysis of ATP → cross-bridge becomes energised
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Myocyte Contraction
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Events of the Cardiac CycleVENTRICULAR FILLING (DIASTOLE)• Passive filling of the ventricles – Ventricular volume and pressure increases• AV valves are open• Semi lunar valves are closed
ISOVULUMETRIC CONTRACTION (SYSTOLE)• Ventricular pressure> Atrial pressure• Causing the AV valves to close
EJECTION (SYSTOLE)• Ventricular pressure> Atrial pressure• Causing the semi lunar valves to open.
ISOVOLUMETRIC RELAXATION (DIASTOLE)• Both semi lunar and AV valves are closed• When ventricular pressure < atrial pressure, AV valves open http://
www.beltina.org/pics/cardiac_cycle.gif
• Four heart sounds.• Usually only the first two can be heard – ‘LUBB DUBB’
• 1st heart sound = due to the closure of the AV valves• 2nd heart sound = due to the closure of the semi lunar valves
• 3rd heart sound = due to the sudden rapid flow of blood into the ventricles during diastole
• 4th heart sound = due to the flow of blood into the ventricles due to atrial contraction
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Heart Sounds
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ECG Representation
http://www.google.co.uk/imgres?hl=en&sa=X&biw=518&bih=273&tbm=isch&tbnid=1aB0RS0FWjHX0M:&imgrefurl=http://
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Mean Arterial Pressure
MeanArterial
Pressure (MAP)
CardiacOutput
(CO)
TotalPeripheralResistance
(TPR)
= x
MAP = the average arterial blood pressure over an entire cardiac cycle
CO = the volume of blood each ventricle pumpsTherefore, CO = the volume of blood flowing
through either the systemic (or pulmonary) circuit per minute
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Cardiac Output
CardiacOutput
(CO)=
Heart Rate(HR)
xStroke Volume
(SV)
TPR = the sum of the resistances to flow offered by all the systemic blood vessels
The arterioles are the principle site of resistance to vascular flow (their radii can be changed by vascular smooth muscle contraction/relaxation)Therefore, TPR is essentially the same as the Total Arteriolar Resistance
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Total Peripheral Resistance
So, to summarise…
Mean Arterial
Pressure (MAP)
Mean Arterial
Pressure (MAP)
CardiacOutput
(CO)
CardiacOutput
(CO)
TotalPeripheralResistance
(TPR)
TotalPeripheralResistance
(TPR)
Heart Rate(HR)
Heart Rate(HR)
Stroke Volume
(SV)
Stroke Volume
(SV)
Arterial baroreceptors• Stretch-sensitive
receptors• Blood vessel wall
stretch → pressure within blood vessel
• Located in the carotid sinus and aortic arch
• Send neurons to the Medullary Cardiovascular Centre
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Sensors of MAP
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Arterial Baroreceptor Reflex
↑ MAP↑ MAP ↓ MAP↓ MAP
↑ Arterial Baroreceptor Firing↑ Arterial Baroreceptor Firing ↓ Arterial Baroreceptor Firing↓ Arterial Baroreceptor Firing
↓ MAP↓ MAP ↑ MAP↑ MAP
Medullary Cardiovascular Centre Medullary Cardiovascular Centre
Effectors of MAP
Mean Arterial
Pressure (MAP)
Mean Arterial
Pressure (MAP)
CardiacOutput
(CO)
CardiacOutput
(CO)
TotalPeripheralResistance
(TPR)
TotalPeripheralResistance
(TPR)
Heart Rate(HR)
Heart Rate(HR)
Stroke Volume
(SV)
Stroke Volume
(SV)
Effectors of COHeart Rate (HR)• Activity of sympathetic
nerves to heart • Activity of parasympathetic
nerves to heart• Plasma adrenaline
Stroke Volume (SV)• Activity of sympathetic
nerves to heart• Plasma adrenaline• End-diastolic ventricular
volume (preload)– Dependent on venous
pressure
The Peer Teaching Society is not liable for false or misleading information…
Effectors of TPRVasoconstrictors (↑ TPR)• Local
– Endothelin-1
• Neural– Sympathetic nerves
• Hormonal– Adrenaline– Anti-Diuretic Hormone– Angiotensin II
Vasodilators (↓ TPR)• Local
– ↓ O2 (hyperaemia)
– CO2
– NO– Inflammatory mediators
• Neural– Neurons that release NO
• Hormonal– Atrial Natriuretic Peptide