Describe the structure of a human heart and how this enables it to bring blood carrying oxygen to the tissues of the body

The human heart has four chambers, an atria and a ventricle on each side, separated into left and right by a central wall called the septum. The heart is a the pump for our double circulatory system. The right hand side of the heart is responsible for pumping deoxygenated blood to the lungs (the pulmonary circulation) and the left hand side pumps oxygenated blood to the rest of the body (called the systemic circulation). The right atria receives blood from the vena cava which carries blood that has lost much of its oxygen in the tissues of the body. This oxygen is needed for aerobic respiration. Due to pressure building in the atria, the blood will move through a one way atrioventricular valve into the right ventricle. Here the muscular wall contracts and ejects this blood into the pulmonary artery, through a semi-lunar valve, that carries it to the lungs. In the lungs the blood is brought through capillaries that lie adjacent to air sacs called alveoli. This is where gas exchange occurs as oxygen diffuses in and carbon dioxide diffuses out. This newly oxygenated blood then travels to the left hand side of the heart via the pulmonary vein.As the blood collects in the left atria, the pressure increase moves it through the second atrioventricular valve into the left ventricle. This has a thicker wall of muscle, which is an adaptation allowing a sufficient force to be generated to pump the blood around the entire body, now at a higher pressure than in the lungs. The blood leaves the left hand side via the aorta after having passed another semi-lunar valve designed to prevent backflow of blood into the heart. It is this division of the heart that hence enables it to separate the different types of blood and deliver them to the correct regions. It is important to note that both ventricles of the heart contract at the same time which increases the heart's efficiency as a pump.