phase 1a andrew hu + elaine pang the peer teaching society is not liable for false or misleading...

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


Aims and Objectives


Anatomy

• Called the pacemaker• P-wave• Located in the right atrium• Transmits across both atria• Transmission goes to AV node


Sino-atrial node

• Specialised myocytes• Base of the right atrium• Transmit impulse deliberately

slowly (0.1s)• Purely there to allow for atrial

contraction


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


Atrioventricular node


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


Contraction

Energised cross-bridge binds to actin

Cross-bridge moves

ATP binds to myosin → cross bridge detaches

Hydrolysis of ATP → cross-bridge becomes energised


Myocyte Contraction


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


Heart Sounds


ECG Representation

http://www.google.co.uk/imgres?hl=en&sa=X&biw=518&bih=273&tbm=isch&tbnid=1aB0RS0FWjHX0M:&imgrefurl=http://


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


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


Total Peripheral Resistance

So, to summarise…

Mean Arterial

Pressure (MAP)

Mean Arterial

Pressure (MAP)

CardiacOutput

(CO)

CardiacOutput

(CO)


(TPR)


(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


Sensors of MAP


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)


(TPR)


(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


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

phase 1a andrew hu + elaine pang the peer teaching society is not liable for false or misleading...

Documents

bpmthe peer teaching

misleading informationevents

misleading informationaims

misleading informationactin

av valves openhttp

av valves2nd heart sound

pressure increasesav

opensemi lunar valves