Cardiac Cycle Flashcards
What is the SA node?
- Sinoatrial node is a group of cells located in the wall of the right atrium.
- Has the ability to spontaneously produce action potential that travels through the heart via the electrical conduction system.
- Sets the rhythm of the heart (heart’s natural pacemaker).
What is the AV node? And what effect does it have?
Atrioventricular node, is a part of teh elecetrocal conduction systeon of the heart that coordinates the tope of teh heart.
It electrically connects teh right atrium and right ventricle, delaying impulses so that atria have time to eject their blood into ventrcles before ventricular contraction.
Describe briefly the phases of the sino-atrial node pacemaker potentials.
3 phases:
- Phase 4:Pacemaker potentials - the ‘ funny current – If ’
- Phase 0: Voltage gated Ca2+ channels
- Phase 3: Repolarisation
What happens during phase 4 of the SA pacemaker potential graph?
- Funny current is activated after the SA action poteintial, (as the membrane repolarizes below the I(small)f threshold). - this supplies an inward current.
- If – hyperpolarisation activated Na+ channel, causing Na+ influx - slow depolarisation which is responsible for starting the diastolic depolarization phase.
What happens during phase 0 of the SA pacemaker potential graph?
As the cell depolarises it reaches a threshold for voltage gated Ca2+ channels leading to Ca2+ influx. RAPID depolarisation. Voltage-gated Na+ channels not involved as in normal nerve depolarisation.
What happens during phase 3 of the SA pacemaker potential graph?
Activation of voltage-gated K+ channels K+ efflux.establishes a negative resting potential.
Briefly describe the phases in the AV action potentials graph.
- Phase 0: rapid depolarisation Voltage-gated Na+ channels, Na+ influx Voltage-gated Ca2+ channels (VGCCs) start to open slowly - Phase 1: early repolarisation Na+ channels close - Phase 2: plateau phase VGCC’s fully open - Ca2+ influx (prevents instant repolarisation by the Na/K pump) Voltage-gated K+ channels start to open slowly - Phase 3: rapid repolarisation VGCCs channels close K+ channel open fully - K+ efflux - Phase 4: resting phase Na+/K+ pump - Na+ out; K+ in Membrane impermeable to Na+ Membrane permeable to K+
Electrical conduction through the heart
contract)
- Electrical activity generated in SA node spreads out via gap junctions into atria.
- At AV node, conduction is delayed allowing correct filling of ventricles. (allowing the atria to contract).
- Conduction occurs rapidly through bundle of His into ventricles.
- Conduction through Purkinje fibres spreads quickly throughout the ventricles. (atria relax and the ventricles then contract)
cardiac contraction
lectrical activity is generated at SA node and conducted throughout heart.
- Electrical activity is converted into myocardial contraction which creates pressure changes within chambers.
- Blood flows from an areas of high pressure to an area of low pressure – unless flow is blocked by a valve.
- Valves open and close depending on pressure changes in chambers
- Events on the right and left sides of the heart are the same, but pressures are lower on the right.
cardiac cycle - systemic and pulmonary circulation.
- Lung circulation:
(Venae Cavae) - Right atrium – Tricuspid valve (AV) – Right ventricle – Pulmonary (semilunar) valve – Pulmonary arteries - Systemic circulation:
Pulmonary veins – Left atrium – Bicuspid (Mitral) valve (AV) – Left ventricle – Aortic (semilunar) valve – Aorta
Cardiac cycle (i.e. sysole etc)
- Diastole – Ventricle filling / atrial contraction
- Systole – Ventricular isovolumetric contraction
- Systole – Ventricular contraction and ejection / atrial filling – valves in artery are forced open.
- Diastole – Ventricular isovolumetric relaxation
What is isovolumetric contraction?
The ventricles contract, pressure rises, with no volume change - takes place whilst all heart valves are closed
Cardiac cycle stages names
- Ventricular filling/atrial contraction
- Isovolumetric contraction
- Ejection
- Isovolumetric relaxation
Left ventricular pressure changes
- Contraction of left atrium (during ventricular diastole), ventricular pressure rises slightly.
- Pressure rises during isovolumetric contraction.
- When ventricle pressure > aorta, the aortic valve opens and blood is ejected.
Ventricle empties - Ventricular pressure < aortic valve so valve closes. We then get isovolumetric relaxation and large pressure drop below that of atrium and mitral valve opens.
Left ventricular volume changes
- Filling ventricle contraction of atria. EDV (End Diastolic Volume) 120ml.
- Full ventricle, higher pressure closes mitral valve.
Systole begins, no change in volume. - Ventricular pressure overcomes aortic valve and bloods ejected.
- When ventricular pressure falls, the aortic pressure closes aortic valve, isovolumetric ventricular relaxation.
