The heart is placed behind the breast bone and within the ribs (thoracic cage) with the lungs on either side. It is a hollow muscular organ made up of flat muscles (myocardium). It is enclosed in a sac known as the pericardium (outside layer), and shaped like an egg, is about the size of a person's clenched fist and weighs colse to 300 g. In a man and 250 g. In a woman.
The heart has four chambers, two atria (upper) and ventricles (lower). Valves associate the upper and lower chambers. A valve is like a one-way door that allows blood to flow only in one direction. The right and left side of the heart are totally separated by a muscular wall and there is no communication in the middle of them. The right side of the heart receives deoxygenated (impure) blood collected from distinct parts of the body straight through small and big veins which enter the lungs. In the lungs blood is oxygenated and carbon dioxide and metabolic waste are removed. The left side of the heart gets oxygenated (pure) blood from the lungs and supplies it to the entire body straight through the major blood vessel (aorta) and its innumerable branches (arteries and capillaries). The left ventricle generates considerably grater pressure than the right ventricle, to enable the blood to be pumped throughout the body. Hence the left ventricle is thicker and muscular, it is the largest of the four chambers and needs requisite blood and oxygen supply. Blood carries cusine and oxygen to each and every cell and tissue of the body. Like any other tissue, the heart muscle also needs a good provide of oxygenated blood. This is done straight through two major coronary arteries which are placed as a crown on the heart. They pursue a wavy policy to adapt themselves to the beating heart. The coronary arteries branch out (left and right coronary arteries) from the root of the aorta near its origin from the left ventricle. The left coronary artery supplementary gets divided into two main branches near its origin itself. Both the coronary arteries branch off into smaller vessels which are distributed all over the covering of the heart. The left ventricle, the requisite and largest chamber of the heart receives the maximum blood supply.
The coronary blood flow in a normal adult averages 200-250 ml/minutes(4-5% of cardiac output). In a wholesome adult at rest, the heart pumps practically 5 liters of blood every minute. Each heart beat is a act of blood being pumped out of the heart. For effective pumping, it is requisite for the heart to beat at a uncostly rate of 60-90 beats/minute which is achieved straight through controlled electrical impulses (conduction system)
The normal pressure of blood against the walls of the arteries is called blood pressure. The normal pressure, when the heart contracts, is called systolic pressure and is in the middle of 100-140 mm of mercury. Then the heart relaxes the pressure is known as diastolic pressure and lies in the middle of 70-90 mm of mercury. Blood pressure is ordinarily expressed as systolic/diastolic, for example 100/70, or 140/90 mm of mercury. In its strenuous daily disposition the heart pauses for rest for a split second in the middle of beats. The heart and the blood vessels together constitute the cardiovascular system.
