Structure of the Heart
# Diagram of Heart Structure
# Cardiac Cycle
AV = Atrioventricular SL = Semi-Lunar
This is the sequence of events in one heart beat
filling phase (diastole)
- atria and ventricles are relaxed
- blood enters heart via pulmonary vein and vena cava
- blood flows passively from atria to ventricles (AV valves open)
- SL valves are closed from previous contraction
atrial contraction (systole)
- atria contract simultaneously
- forces remaining blood from atria into ventricles
- AV valves close
ventricular contraction (systole)
- AV and SL valves are closed
- ventricles contract from the apex (base) upwards
- blood forced out of aorta and pulmonary artery, SL valves open
- “lub”: AV valves closing as ventricles contract
- “dub”: SL valves closing as ventricles contract
# Control of the Cardiac Cycle
- sinoatrial node (SAN)
- located in the right atrium
- group of cells that can initiate their own impulse (cardiac muscle is myogenic because of this ability)
- Electrical activity from SAN spreads through both atria—triggering a contraction of the atria.
- Electrical activity can’t pass through the atrioventricular septum, but can pass through the atrioventricular node (AVN).
- A short delay before AVN conducts electrical activity down to the base of the ventricles (ensures atria finish contracting and ventricles are full of blood).
- Electrical activity travels to base of ventricles (ensures atria finish contracting and ventricles are full of blood).
- Electrical activity travels to the base of ventricles via the bundle of His.
- Ventricles contract from the base upwards.