The Heart

The heart is a muscular and the most powerful organ responsible for pumping blood round the body. The heart lies in the chest just behind the breast bone and in between the two lungs. It enclosed in a two layers tough membrane called PERICARDIUM. The space between the two layers is filled with pericardial fluid. The fluid reduces the friction caused by the pumping movement of the heart between the heart wall and special muscle called the CARDIAC MUSCLE   which enable it go on pumping.

THE STRUCTURE OF THE HEART 

The heart has four chambers: the two upper thin wall auricles and the two lower thick wall ventricles. The right side of the heart is completely separated from the left side by a wall called the SEPTUM. Two large veins, i.e. the superior (vena cava and the inferior  vena cava bringing back red deoxygenated blood from the various parts of the body except the lungs open into the right auricle.

The Pulmonary veins bringing bright red oxygenated blood from the lungs open into the left auricle. The right auricle opens into the right ventricle. The opening is guarded by tricuspid valve. This valve has three flaps which are attached by cord-like tendon called chordate tendinae to the wall of the ventricle. The opening of the left auricle into the left ventricle is guarded by bicuspid valve. This valve is functionally and structurally similar to tricuspid valve except that it has two flaps instead of three.

The right ventricle opens into the pulmonary artery which branches into two. One leading to the right lungs and the other leading to the left lungs. These carry deoxygenated blood to the lungs. The left ventricle opens into the large AORTA which branches to distribute oxygenated blood to all parts of the body except the lungs. Semi-lunar valves in the arteries prevent back-flow of blood from the arteries into the ventricle.