Describe the role of the heart and lungs in the oxygenation of blood in humans. Why is oxygen is essential for the functioning of the human body.

The main purpose of oxygen in the body is for respiration. Respiration is a biochemical reaction, by which the body produces energy in the form of ATP to complete both cellular and other functions. This process uses oxygen and glucose and produces carbon dioxide and water as waste products. Humans breathe in oxygen from the air through their mouth and nose, this then passes down their trachea, into the bronchi, bronchioles and then finally into the alveoli in their lungs. Alveoli are one cell thick, and this allows the easy diffusion of oxygen into the capillaries that surround them. These capillaries contain deoxygenated blood that has been pumped from the heart via the pulmonary artery. Oxygen from the alveoli diffuses into the capillary blood, which then travels back to heart and into the left atrium, via the pulmonary vein. When the heart contracts the oxygenated blood is pushed into the left ventricle and then into the aorta where it is then circulated round the body to all cells, to be used for respiration, this is known as systemic circulation. The deoxygenated blood is then pumped back to the heart and into the right atrium via the vena cava. When the heart contracts this blood is pumped into the right ventricle then the pulmonary artery to be circulated to the capillaries surrounding the alveoli again, this is pulmonary circulation. The process then repeats.