Cardiac Cycle Flashcards
what is convection?
→Convection is the mass movement of fluid caused by pressure differences.
what are the main functions of the heart, arteries, capillaries and veins in the context of circulation?
→HEART: driving force (creates large pressures)
→ARTERIES: distribution (mostly in parallel to alter blood flow)
→CAPILLARIES: exchange (found in huge number, thin for ease of movement)
→VEINS: reservoir (2/3rd of the blood volume stored in veins and venules)
describe the Sinoatrial Node (SAN)
The SA node is a group of cells located in the walls of the right atrium.
what are the functions of the SAN?
→ action potentials that travel through the heart via the electrical conduction system.
→It sets the rhythm of the heart
→known as the heart’s natural pacemaker
→The rate of action potential production (and therefore the heart rate) is influenced by nerves that supply it.
what are the phases of the SAN pacemaker potentials?
PHASE 4: PACEMAKER POTENTIALS
→ “funny current (If)”
→At the end of an SA action potential, the membrane repolarises below the If threshold ( -40/50 mV)
→At -50mV an Na+ channel is activated, causing Na+ influx and slow depolarisation
PHASE 0: VOLTAGE-GATED CA2+ CHANNELS
→As the cell depolarises, it reaches a threshold for voltage-gated Ca2+ channels
→ leading to a Ca2+ influx
→making the inside less negative
→RAPID depolarisation
→Voltage-gated Na+ channels are not involved
PHASE 3: REPOLARISATION →The calcium channels switch off. →activation of voltage-gated K+ channels → K+ efflux → repolarising the cell
what are the phases of atrial/ventricular action potentials?
PHASE 0: RAPID DEPOLARISATION
→Voltage-gated Na+ channels open, causing a Na+ influx.
→Voltage-gated Ca2+ channels start to open slowly.
PHASE 1: EARLY REPOLARISATION
→Na+ channels close.
PHASE 2: PLATEAU PHASE
→Voltage-gated calcium channels are now fully open, causing a Ca2+ influx.
→The voltage-gated K+ channels start to open slowly.
PHASE 3: RAPID REPOLARISATION
→Voltage-gated calcium channels close.
→K+ channels open fully, causing a K+ efflux.
PHASE 4: RESTING PHASE
→The Na+/K+ pump works to get Na+ out and K+ in.
→The membrane is impermeable to Na+ but permeable to K+, which helps establish the equilibrium.
describe the electrical conduction through the heart
Electrical activity generated in the SA node spreads out via the gap junctions into the atria.
2) At the AV node, conduction is delayed to allow the correct filling of the ventricles.
3) Conduction occurs rapidly through the bundle of His into the ventricles.
4) Conduction occurs through the Purkinje fibres and spreads quickly throughout the ventricles.
Ventricular contraction begins at the apex
P WAVE
atrial depolarisation
PR SEGMENT
AV node delay
QRS COMPLEX
ventricular depolarisation (atria repolarising simultaneously)
ST SEGMENT
time during which ventricles are contracting and emptying
T WAVE
ventricular repolarisation
TP INTERVAL
time during which ventricles are relaxing and filling
where is electrical activity generated and what is it converted into?
→electrical activity is generated at the SA node and conducted throughout the heart
→electrical activity is converted into myocardial contraction which creates pressure changes within chambers
where does blood flow from usually (pressure) ?
blood flows from an area of high pressure to low pressure
→unless the flow is blocked (by a valve, for example)