Atrioventricular (AV) Valves: Located between the atria and ventricles (Tricuspid on the right, Bicuspid/Mitral on the left). These valves open to allow blood into the ventricles and snap shut during ventricular contraction to prevent backflow into the atria.
Semilunar Valves: Located at the exits of the heart (Pulmonary and Aortic valves). These prevent blood from flowing back into the ventricles from the arteries once the heart relaxes.
Pressure-Driven Operation: Valves operate passively based on pressure gradients. When pressure in a preceding chamber exceeds the pressure in the succeeding chamber/vessel, the valve opens; when the pressure reverses, the valve is forced shut.
Sinoatrial Node (SAN): Known as the primary pacemaker, the SAN initiates a wave of electrical excitation that spreads across the atria, causing them to contract simultaneously (atrial systole).
Atrioventricular Node (AVN) Delay: The electrical signal is delayed at the AVN for approximately to seconds. This delay is vital as it ensures the atria have fully emptied their blood into the ventricles before ventricular contraction begins.
Purkyne Tissue and Bundle of His: After the delay, the signal travels down the septum via the Bundle of His to the apex (bottom) of the heart. It then spreads upward through Purkyne fibers, causing the ventricles to contract from the bottom up, efficiently squeezing blood into the major arteries.
| Feature | Atria | Ventricles |
|---|---|---|
| Wall Thickness | Thin muscular walls | Thick muscular walls |
| Function | Receive blood and prime ventricles | Pump blood out of the heart |
| Pressure Generated | Low pressure | High pressure |
| Feature | Right Ventricle | Left Ventricle |
|---|---|---|
| Destination | Lungs (Pulmonary) | Body (Systemic) |
| Wall Thickness | Thinner | Much Thicker (approx. 3x) |
| Pressure | Lower pressure to protect lung tissue | Very high pressure to overcome resistance |
The 'Left-Right' Rule: Always remember that diagrams show the heart as if it were in a patient facing you. The 'Left' side of the heart is on the right side of your paper.
Vessel Identification: Arteries always carry blood Away from the heart (A for Away). Veins always carry blood Towards the heart. Note the exception: the pulmonary artery is the only artery carrying deoxygenated blood.
Pressure Graphs: In exams, you may see pressure-volume loops. Always check where the lines cross; these intersection points represent the opening and closing of specific valves.
Wall Thickness Logic: If asked why the left ventricle is thicker, always mention the need to overcome high resistance in the systemic circulation and the requirement for high pressure to reach all body tissues.
