The heart pumps blood round the circulatory system. It lies inside the thoracic cavity and is surrounded by the membrane called pericardium. The pericardium is filled with a fluid called pericardic fluid which limits or reduce friction. In mammals and birds, the heart is completely divided into left and right by the septum.
The heart is a muscular bag and it contains 4 chambers:
- The left and right auricles
- The left and right ventricles.
Oxygenated blood are confined to the left side of the heart while the deoxygenated blood are confined to the right side. The opening between the left auricle and the left ventricle is guided by the biscpid valve which is so named because it contains 2 membranous flaps. The opening between the right auricle and the left ventricle is guided by the tricuspid valve which is so named because it contains 3 membranous flaps. The walls of the ventricle are thicker than the wall of the auricle.
The 2 largest veins, superior Vena cavalier and inferior Vena cava transports the deoxygenated from the various parts of the body (except the lungs) into the right auricle. Oxygenated blood is transported into the left auricle from the lungs through the pulmonary veins. Deoxygenated blood is transported into the lungs through the pulmonary artery from the right ventricle. Oxygenated blood is transported to all parts of the body (except the lungs) through the aorta (the largest artery) from where the carotid artery supplies the head. The left ventricle has a thicker wall than the right ventricle because it is involved in a larger systemic circulation while the right is involved in the smaller pulmonary circulation.