External Structure of heart: Human heart is a four-chambered organ, with two auricles and two ventricles. It lies in the thoracic cavity, in between the two lungs. Its weight is about 300 gm. It remains enclosed in a double-walled membranous sac called pericardium. An interarterial and interventricular septum separate left and right side of the heart. Auricles are the upper chambers, and ventricles are lower chambers. Auricles are thin-walled and receive blood from four pulmonary veins and two vena- cava. Left auricle opens into the left ventricle, through an auricula- ventricular opening, guarded by a pair of flaps called the bicuspid valve. Similarly, tricuspid valve guards the aperture between the auricle and the ventricle. The left ventricle opens into the aorta, while the right ventricle opens into the pulmonary artery.
Internal Structure of Heart: Heart is the muscular pumping organ that circulates blood through the body, internally. It is divided into four chambers, namely, the right and left atria or auricles and right and left ventricles. The right and left sides of the heart are separated and do not
The upper chamber, the auricles or atria, are relatively thin-walled, receive blood from the veins. Oxygenated blood from the lungs enters the left atrium, the pulmonary veins and deoxygenated blood from the body enters the right atrium, from the vena- cava. The left atrium is connected to the left ventricle through a valve. Similarly, the right atrium is connected to the right ventricle, through another valve. These valves prevent the backflow of blood into atria when the ventricles contract to pump blood out of the heart to the rest of the body. All the atria and ventricles of the heart contract and relax at appropriate times and makes heart behave like a pump. A pericardium sheath protects the muscular heart. The chamber of the heart is separated by partition septum.
