External and Internal Structures of the heart
The atrioventricular (AV) valves link the atria to the ventricles, and the semi-lunar (SL) valves link the ventricles to the pulmonary artery and aorta - they all stop blood flowing the wrong way.
The valves only open one way - whether they're open or closed depends on the relative pressure of the heart chambers. If there's higher pressure behind a valve, it's forced open. If pressure is higher in front of the valve, it's forced shut.
Thickness of Heart Chamber Walls
The heart is mainly cardiac muscle. When it contracts it creates higher pressure - enough to force blood all the way around the boyd.
Each of the four chambers of the heart have a different function. The more work a heart chamber has to do, the muscle it needs - so thicker walls. The left ventricle of the heart has thicker more muscular walls than the…