Double circuit.

Human heart functions as a double pump, and is responsible for pulmonary and systemic circulation. Separation of blood. Complete separation of deoxygenated blood (Right side) and oxygenated blood (left side), in the heart, is maintained.

Blood Circulation.

Right atrium It receives deoxygenated blood via venae cavae from the body. Right ventricle and tricuspid valve. The blood is passed on to right ventricle through tricuspid valve (called so because it has 3 flaps). These flaps are attached with fibrous cords called chordae tendinae, to the papillary muscles which are extensions of the wall of the right ventricle.

Pulmonary trunk and Semilunar valve.

When right ventricle contracts, the blood is passed to pulmonary trunk, which Aortic Arch. The aorta forms an arch, and before descending down gives three branches supplying blood to head, arms and shoulders. It gives many small branches to the chest wall and then passes down to the abdominal region. Here it gives branches, which supply blood to different parts of alimentary canal, kidneys and the lower abdomen.

Iliac arteries.

The aorta Bifurcates into iliac arteries, each of which leads to supply blood to each legs. Superior Vena Cava The blood from the upper part of the body is collected by different veins, which join to form superior vena cava; which pass its blood to the right atrium.

Inferior vena cava.

Two Iliac veins are formed by veins which collect blood from legs, and unite to from inferior vena cava. It receives renal vein from each kidney; and hepatic vein from the liver, before it enters the right atrium.

Hepatic Portal Vein.

The liver receives hepatic portal vein which is formed by many veins collecting deoxygenated blood with absorbed food from different parts of alimentary canal. carries blood via left and right pulmonary arteries, to the lungs. At the base of the pulmonary trunk, semilunar valves are present. Pulmonary veins and Left atrium. After oxygenation in lungs the blood is brought by pulmonary veins to the left atrium, which passes this blood via bicuspid valve (called so because it has two laps) to the left ventricle.

The flaps of bicuspid valve are similarly attached through chordae tendinae, to papillary muscles of the wall of left ventricle.

Left ventricle and Aorta.

When the left ventricle contracts, it pushes the blood through aorta to all parts of the body (except lungs). The wall of left ventricle is thicker (about 3 times) than that of the right ventricles.

Aortic Semilunar valve.

At the base of aorta semilunar valves are also present. The valves of the heart control the direction of flow of blood. Coronary Arteries. At the base of aorta, first pair of arteries, the coronary arteries, arise, and supply blood to the heart.