The Circulatory System and the Heart

The human circulatory system is a double circulation, meaning blood passes through the heart twice for each complete circuit of the body. The pulmonary circuit carries deoxygenated blood to the lungs and returns oxygenated blood to the heart, while the systemic circuit delivers oxygenated blood to the body tissues and returns deoxygenated blood. Double circulation maintains high pressure in the systemic circuit, allowing efficient delivery to distant tissues.

Structure of the Heart

The heart is a muscular pump made of cardiac muscle, or myocardium, which contracts without fatiguing. It has four chambers: two upper atria that receive blood and two lower ventricles that pump blood out. The right side handles deoxygenated blood and the left side handles oxygenated blood; a wall called the sep