Heart

It is the major pumping organ associated with the circulatory system. Human heart contains four chambers, upper two are called Auricles and are divided by an auricular septum into left and right and lower two are called ventricles divided into two by the ventricular septum into left and right. In mammalian heart right side is responsible for collecting impure blood and left side is responsible for collecting pure blood.

One thin membrane covers the heart externally that is called pericardial membrane. The cavity between this membrane and heart wall is called pericardial cavity that is filled with thick, gelatinous fluid called pericardial fluid. Pericardial fluid protects the heart from external injury, keeps heart moist and makes movement heart frictionless.

Parts of heart:

1. Right auricle: It receives deoxygenated blood from different parts of the body and pumps it into the right ventricle.
2. Right ventricle: It receives deoxygenated blood from the right auricle and pumps into the lungs for it to become oxygenated.
3. Left auricle: It receives pure oxygenated blood from lungs and pumps it to left ventricle
4. Left ventricle: It receives oxygenated blood from left auricle and pumps it to different parts of the body.

Functions of four blood vessels of the heart:

1. Vena cava: Vena cava transport deoxygenated blood from different parts of the body into the right auricle of the heart.
2. Pulmonary arteries: They carry deoxygenated plod from the right ventricle of the heart to the lungs for oxygenation.
3. Pulmonary vein: They carry oxygenated blood from lungs to the left auricle of the heart.
4. Aorta: It carries pure oxygenated blood from the left ventricle of the heart.

Functions of four valves of heart:

1. Tricuspid / Right atrioventricular valve: It blocks the backflow of blood from the right ventricle to the right auricle when right ventricle contracts.
2. Bicuspid / Mitral / Left atrioventricular valve: It blocks the backflow of blood from the left ventricle to the left auricle when left ventricle contracts.
3. Pulmonary / Pulmonic valve: It blocks the backflow of blood from pulmonary artery to the right ventricle when ventricle relaxes.
4. Aortic valve: It blocks the backflow of blood from the aorta to the left ventricle relaxes.

Working of heart:

Wall of right atrium contains natural pacemaker from where the waves of contraction of the heart start. The heart pumps blood with the help of regular contraction and relaxation. During circulation blood flows following route:

Impure blood in right auricle ----- >Right ventricle ( by opening of Tricuspid valve) ------> Pulmonary artery (by the opening of pulmonary valve) -------> Lungs ( Oxygenation) -------> Pulmonary vein ------> Left auricle ------> Left ventricle ( by opening of bicuspid valve) -------> Aorta ( by opening of Aortic valve) -------> tissues of body (exchange of gases and waste products) --------> Vena cava -------> Right auricle