Chambers of the Heart
The heart is divided into two halves by a muscular wall or septum, the right heart and the left heart. The function of the right heart is to collect all venous return and propel it into the pulmonary vasculature. The function of left heart is to receive blood from pulmonary vasculature and propel it into systemic circulation.
Each half has an upper collecting chamber, the atrium and lower pumping chamber-the ventricles. The right atrium is a thin-walled chamber that has a small amount of myocardium, therefore it can accommodate changes in venous returns. The right atrium that serves as a reservoir for venous blood returning to the heart via the superior and inferior venacava and the coronary sinus. It stores blood during right ventricular systole (contractions). The right ventricle receives venous blood form the right artium during ventricular diastole (relaxation) and then propels this blood through the pulmonary valve into the pulmonary artery. The overall workload of right ventricle is less than that of left ventricle because the pulmonary system is a low-pressure system.
The thin-walled left atrium receives oxygenated blood from the four pulmonary veins and serves as a reservoir during left ventricular systole. Blood flows by gravity from left atrium into the left ventricle through the opened mitral valve during ventricular diastole. Blood is then ejected from the left ventricle through the opened aortic valve into the sustemic circulation during ventricular systole. The ventricle has thick walls because it must contract against a high pressure systemic circulation to deliver blood to the peripheral tissues.