Energy and Waste

In order to perform internal cellular processes, the cells require a constant energy supply. This is mainly provided by the breakdown of fats and carbohydrates. Using oxygen, the fuel is `burned' (oxidised) via a number of biochemical pathways to provide energy, yielding a number of waste products.
The blood circulatory system provides a link between the various organs in the body. The left side of the heart (left ventricle) pumps blood rich in oxygen to the organs through the arteries. The cells then use the oxygen to burn the fuels which are also circulating in the blood to produce energy. One of the most abundant waste products, carbon dioxide, has to be removed to avoid poisoning the cells, so it is returned to the right side of the heart (right ventricle). From here, the carbon dioxide rich blood is pumped to the lungs where it is breathed out and replaced with fresh oxygen. If the requirement for oxygen increases, so the breathing and heart rates increase. As requirements decrease, so breathing and heart rate decrease.