Contractions of the heart are synchronized so both atria contract to load the ventricles and then both ventricles contract to push blood into the pulmonary and systemic circuits. (Note: the septum dividing the two sides of the heart is muscle shared by both ventricles. During contraction, it provides force for both ventricles at the same time.)
The valves between each atrium and ventricle are called atrioventricular (AV) valves. Stringy fibres called chordae tendineae prevent the flaps of the AV valves from inverting. The AV valve on the right side of the heart has three flaps and is called the tricuspid valve. The AV valve on the left side of the heart has two flaps and is called the bicuspid or mitral valve. The valves that allow blood to pass from the ventricles to the pulmonary trunk (pulmonic valve) and the aorta (aortic valve) are called semilunar valves.
The cardiac muscle fibres that make up the heart are unique. The heartbeat (called a cardiac cycle) is initiated and synchronized by special nodal tissue that is part muscle and part nerve, and the heart beat does not depend on the nervous system. The heartbeat and its control is the topic of the next lesson.
deoxygenated blood is returned to the right atrium from the body
the right atrium pumps the blood through the atrioventricular valve into the right ventricle
the right ventricle pumps blood through the semilunar (pulmonic) valve into the pulmonary truck and into the pulmonary arteries to both lungs
oxygenated blood is returned to the left atri via the pulmonary veins
the left atrium pumps the blood through the atrioventricular valve into the left ventricle
the left ventricle pumps the blood under high pressure through the semilunar (aortic) valve to the body
Note that the contraction of both sides of the heart occurs together. Both atria contract and then both ventricles contract. The pathway of blood through the heart is something you will need to be able to describe.
name a function of each structure of the heart identified in the lesson
describe the path of blood through the heart, including the valves it passes through