WORKING OF HEART

Pumping blood to the lungs. Blood from the body that enters the right side of the heart contains carbon dioxide, a gaseous waste the cells produce in creating energy. Blood enters the right atrium through the superior vena cava and inferior vena cava. The atrium fills with blood and then contracts, squeezing the blood through the tricuspid valve into the right ventricle. After the ventricle is filled, pressure forces the tricuspid valve to close and the pulmonic valve, leading to the pulmonary artery, to open. The ventricle contracts, and the blood gushes through the pulmonary artery and into the lungs. In the lungs, carbon dioxide is removed from the blood and oxygen is added. The oxygenated blood then flows through the pulmonary veins to the left side of the heart.

Pumping blood throughout the body. Oxygenated blood from the lungs enters and fills the left atrium. The atrium then contracts, which squeezes the blood through the mitral valve into the left ventricle. After blood fills the ventricle, the mitral valve closes and the aortic valve opens. Blood pours into the aorta and flows through arteries to the body tissues. Other blood vessels transport blood between the heart and lungs. Pulmonary veins return blood from the lungs to the left atrium. The pulmonary artery carries blood from the right ventricle to the lungs. The aorta is the largest artery. It receives oxygenated blood from the left ventricle and, through numerous branches, distributes it throughout the body. The pulmonary artery and the aorta are sometimes called the great vessels.
The first arteries that branch from the aorta are the two major coronary arteries.

Valves regulate the flow of blood through the heart. The valves have flaps that open as blood pours from a chamber. When the flaps close, they prevent blood from flowing back into the chamber. Two valves separate the atria and the ventricles. They are called the atrioventricular valves or AV valves. The AV valve between the right atrium and right ventricle has three flaps and is called the tricuspid valve. The AV valve on the left side of the heart has two flaps and is called the mitral valve. The heart also has a valve, called a semilunar valve, between each ventricle and its great vessel--the pulmonary artery or the aorta. Each semilunar valve has three flaps shaped like half moons. When the right ventricle contracts, it delivers blood to the pulmonary artery.

Valves regulate the flow of blood through the heart. The valves have flaps that open as blood pours from a chamber. When the flaps close, they prevent blood from flowing back into the chamber. Two valves separate the atria and the ventricles. They are called the atrioventricular valves or AV valves. The AV valve between the right atrium and right ventricle has three flaps and is called the tricuspid valve. The AV valve on the left side of the heart has two flaps and is called the mitral valve. The heart also has a valve, called a semilunar valve, between each ventricle and its great vessel--the pulmonary artery or the aorta. Each semilunar valve has three flaps shaped like half moons. When the right ventricle contracts, it delivers blood to the pulmonary artery tricuspid and mitral valves open and blood begins to fill the ventricles. The autonomic nervous system controls the heart rate. Special cells send electrical impulses (nerve signals) through the heart, causing it to contract and relax rhythmically. The impulse begins in a small bundle of muscle fibers called the sinoatrial node, or S-A node. The S-A node is often called the pacemaker of the heart because it sets the pace of the heartbeat as it sends out rhythmic signals.