Phase 1A Andrew Hu + Elaine Pang The Peer Teaching Society is not liable for false or misleading information…

The tiniest amount of heart anatomy Activation and Contraction Cardiac Cycle Control of MAP The Peer Teaching Society is not liable for false or misleading information… Aims and Objectives

The Peer Teaching Society is not liable for false or misleading information… Anatomy

The Peer Teaching Society is not liable for false or misleading information… Anatomy

Called the pacemaker P-wave Located in the right atrium Transmits across both atria Transmission goes to AV node The Peer Teaching Society is not liable for false or misleading information… Sino-atrial node

Specialised myocytes Base of the right atrium Transmit impulse deliberately slowly (0.1s) Purely there to allow for atrial contraction The Peer Teaching Society is not liable for false or misleading information… 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 – bpm The Peer Teaching Society is not liable for false or misleading information… Atrioventricular node

The Peer Teaching Society is not liable for false or misleading information… Actin and Myosin Troponin C – calcium binds to cause conformational change in Troponin I Troponin T – Binds to tropomyosin forming a tropomyosin troponin complex Troponin I – binds to actin, to hold the tropomyosin – troponin complexes in place

1.Excitation 2.L Type Ca channels in T tubules open causing influx of Ca 3.Ca binds to sarcoplasmic opening lateral sacs releasing more Ca 4.Ca binds to TnC moving tropomyosin 5.Allows energized myelin to bind to actin 6.Repolarization and Ca reuptaken The Peer Teaching Society is not liable for false or misleading information… Contraction

Energised cross-bridge binds to actin Cross-bridge moves ATP binds to myosin → cross bridge detaches Hydrolysis of ATP → cross-bridge becomes energised The Peer Teaching Society is not liable for false or misleading information… Myocyte Contraction

The Peer Teaching Society is not liable for false or misleading information… Events of the Cardiac Cycle VENTRICULAR 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 org/pics/cardiac_cy cle.gif

Four heart sounds. Usually only the first two can be heard – ‘LUBB DUBB’ 1 st heart sound = due to the closure of the AV valves 2 nd heart sound = due to the closure of the semi lunar valves 3 rd heart sound = due to the sudden rapid flow of blood into the ventricles during diastole 4 th heart sound = due to the flow of blood into the ventricles due to atrial contraction The Peer Teaching Society is not liable for false or misleading information… Heart Sounds

The Peer Teaching Society is not liable for false or misleading information… ECG Representation ?hl=en&sa=X&biw=518&bih=27 3&tbm=isch&tbnid=1aB0RS0F WjHX0M:&imgrefurl=

The Peer Teaching Society is not liable for false or misleading information… Mean Arterial Pressure Mean Arterial Pressure (MAP) Cardiac Output (CO) Total Peripheral Resistance (TPR) = x MAP = the average arterial blood pressure over an entire cardiac cycle

CO = the volume of blood each ventricle pumps Therefore, CO = the volume of blood flowing through either the systemic (or pulmonary) circuit per minute The Peer Teaching Society is not liable for false or misleading information… Cardiac Output Cardiac Output (CO) = Heart Rate (HR) x Stroke 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 The Peer Teaching Society is not liable for false or misleading information… Total Peripheral Resistance

So, to summarise… Mean Arterial Pressure (MAP) Mean Arterial Pressure (MAP) Cardiac Output (CO) Cardiac Output (CO) Total Peripheral Resistance (TPR) Total Peripheral Resistance (TPR) Heart Rate (HR) Heart Rate (HR) 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 The Peer Teaching Society is not liable for false or misleading information… Sensors of MAP

The Peer Teaching Society is not liable for false or misleading information… Arterial Baroreceptor Reflex ↑ MAP ↓ MAP ↑ Arterial Baroreceptor Firing ↓ Arterial Baroreceptor Firing ↓ MAP ↑ MAP Medullary Cardiovascular Centre

Effectors of MAP Mean Arterial Pressure (MAP) Mean Arterial Pressure (MAP) Cardiac Output (CO) Cardiac Output (CO) Total Peripheral Resistance (TPR) Total Peripheral Resistance (TPR) Heart Rate (HR) Heart Rate (HR) Stroke Volume (SV)

Effectors of CO Heart 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 TPR Vasoconstrictors (↑ TPR) Local – Endothelin-1 Neural – Sympathetic nerves Hormonal – Adrenaline – Anti-Diuretic Hormone – Angiotensin II Vasodilators (↓ TPR) Local – ↓ O 2 (hyperaemia) – CO 2 – NO – Inflammatory mediators Neural – Neurons that release NO Hormonal – Atrial Natriuretic Peptide