The mammalian heart pumps blood around the body and to the lungs. It is the main component of the blood circulatory system and is divided into four main chambers. The upper two chambers are called atria and the lower two are called ventricles. The septum separates the atria and ventricles in a way that oxygenated and deoxygenated blood do not mix. Hence, the right side of the heart has deoxygenated blood, while the left side has oxygenated blood (right side of heart is on the left of page and left side of the heart is on the right of page). The ventricles have thicker muscles than the atria because they need to pump blood at a greater distance, while atria just need to pump blood into the ventricles which is a short distance. Also, the atrioventricular and semilunar valves are present so backflow of blood is avoided. Moreover, within the heart there are tiny coronary arteries that supply the heart with fresh oxygen.
The flow of the blood through the heart will be explained below in two classifications; right side and left side of the heart.
1. The deoxygenated blood (coming from the body) enters the heart through superior and inferior vena cava into the right atrium. The superior vena cava collects blood from the upper part of the body while the inferior vena cava collects from the lower part.
2. Once the blood starts to enter, pressure increases in the atria and it contracts, and the tricuspid valve opens and blood flows into the right ventricle.
3. Again, when pressure starts to rise in the ventricle, the ventricle contracts; closing the tricuspid valves and the semilunar valves in the pulmonary artery open.
4. Hence, the pulmonary artery takes the blood to the lungs where gas exchange happens.
1. The deoxygenated blood becomes oxygenated when oxygen diffuses inside the capillaries from the alveolus and carbon dioxide diffuses outside the blood, into the alveolus where it is diffused out of the body.
2. Then the oxygenated blood is brought to the left atria with the help of pulmonary vein.
3. Again, when pressure starts to rise in the left atria; the bicuspid valves open and blood flows into the left ventricle.
4. Then, the blood pressure rises in ventricles and they contract, causing bicuspid valves to close, and semilunar valves in the aorta to open.
5. Hence, blood flows to the rest of the body through the aorta, and then the semilunar valves close back.
Structure of the Heart (Arrows show the flow of blood)