Structure of the heart:
The heart is a muscular organ composed of four chambers. The two upper chambers are called auricles or atrium and the two lower chambers are called ventricles.
The walls of the auricles are relatively thin when compared to the ventricles, as the auricles only pump blood to the ventricles but the ventricles pump blood to all parts of the body.
The wall of the left ventricle is thicker when compared to the wall of the right ventricle, as the right ventricle only pumps blood up to the lungs but the left ventricle has to pump blood to long distances in the body including the tips of the fingers and toes and up to the brain against gravity.
The protective covering of the heart is called the pericardium. The pericardial fluid present between the two layers of the pericardium helps to reduce friction and protect the heart.
Valves of the heart:
The heart pumps blood and need valves to regulate the flow of blood in a single direction. The heart has four valves-tricuspid valve, bicuspid valve, pulmonary semi-lunar valve and aortic semi-lunar valve.
The tricuspid valve is present at the opening between the right auricle and the right ventricle. It checks the back flow of blood from the right ventricle to the right auricle. The valve has three thin triangular leaf-like flaps or cusps, so it is called the tricuspid valve. The tricuspid valve is also called the right auriculo - ventricular valve.
The bicuspid valve is present at the opening between the left auricle and the left ventricle. It checks the back flow of blood from the left ventricle to the left auricle. The valve has two cusps, so it is called bicuspid valve. The bicuspid valve is also known as the mitral valve or the left auriculo ventricular valve.
The valves between the auricles and the ventricles have strong cords (tendons) attaching them to the wall of the ventricles. These tendons are called chordae tendinae and arise on the muscular projections of the ventricle wall called papillary muscles.
The pulmonary semi - lunar valves are present at the point of origin of the pulmonary artery from the right ventricle. They are three in number and half moon or pocket shaped.
Aortic semi - lunar valves are located at the point of origin of aorta from the left ventricle. They are three in number and half moon or pocket shaped.
Blood vessels of the heart:
The main blood vessels that carry blood away from the heart are the aorta and the pulmonary artery.
Aorta arises from the left ventricle and carries oxygenated blood to all parts of the body.
Pulmonary artery arises from the right ventricle and carries deoxygenated blood to the lungs for oxygenation. Arteries usually carry oxygenated blood. Pulmonary artery is an exception as it carries deoxygenated blood.
Blood vessels entering the heart are the superior vena cava, the inferior vena cava and the four pulmonary veins.
The right auricle receives the superior vena cava and the inferior vena cava. Superior vena cava brings de - oxygenated blood from the upper regions of the body, which include the head, chest and arms. Inferior vena cava brings de - oxygenated blood from the lower regions of the body, which include the abdomen and legs.
The left auricle receives the four pulmonary veins - two from each lung.
The pulmonary veins bring oxygenated blood from the lungs. Veins usually carry de-oxygenated blood. Pulmonary veins are an exception as they carry oxygenated blood.
Two coronary arteries, which arise from the base of the aorta, supply the muscles of the heart. A blockage in the coronary arteries or its branches eventually leads to a heart attack.
The flow of blood in the heart:
The superior vena cava and the inferior vena cava, the two largest veins in the body, collect de-oxygenated or impure blood from the various parts of the body. The impure blood of the vena cavae is received by the right auricle. The blood then enters the right ventricle through the tricuspid valve and is pumped into the pulmonary artery. The pulmonary artery is the only artery in the body that carries de-oxygenated blood. Semi-lunar valve guards the opening of the pulmonary artery. The pulmonary artery divides to form the left pulmonary artery and the right pulmonary artery, which carries the blood to the right and left lung respectively for oxygenation.
The oxygenated blood is returned to the left auricles via the four pulmonary veins, that is, two veins from each lung. The pulmonary veins are the only veins in the body that carries oxygenated blood. The blood then enters the left ventricle through the bicuspid valve, from where it is pumped into the largest artery of the body, the aorta for circulation to various parts of the body. Aortic semi-lunar valve guards the opening of the aorta.
The right side of the heart is concerned with the circulation of the de-oxygenated blood whereas the left side of the heart is concerned with the circulation of oxygenated blood.