Energy means, it is the ability to do work. Energy metabolism is the process by which energy is produced and transformed. Food provides the source of energy. We need energy to move the muscles in the body to carry out activities. The role of energy in the body is to pull oxygen from the air and diffuse it into our bloodstream. Energy is needed to circulate blood and also to breathe and absorb oxygen. I will now explain the physiology of the cardiovascular system and the respiratory system as it relates to energy metabolism in the body. The Cardiovascular SystemThe cardiovascular system is responsible for replenishing nutrients throughout the body and removing gaseous waste from the body. The cardiovascular system is made up of the heart, blood and blood vessels. Arteries, veins and capillaries are the blood vessels of the cardiovascular system. The heart and its roleThe heart is an organ of the cardiovascular system. The heart is responsible for supplying oxygen to all parts of the body. The heart is the size of a closed fist. It is located just to the side of the center of the chest. It is surrounded by a protective membrane called the pericardium. The heart is divided into left and right sides. The heart is made up of muscles and has walls. It makes contact to pump blood into blood vessels and throughout the body. The heart beats to maintain blood circulation. The heartbeat drives the cardiac cycle and pumps blood to the body's cells and tissues. Veins supply deoxygenated blood from the body to the right side of the heart. Then the heart pumps it back into the lungs, where it absorbs more oxygen. Then the oxygen in the blood returns to the left side of the heart and then pumps it towards the center of the paper... with a large diameter to offer the least resistance to flow. It has valves to prevent low-pressure blood from flowing backwards. Blood circulation There are two types of circulatory systems: pulmonary and systemic. The pulmonary circuit takes blood to the lungs to be oxygenated and then returned to the heart. In the lungs, deoxygenated blood is removed and oxygen absorbed through hemoglobin contained in red blood cells. The systemic circuit transports blood throughout the body to supply oxygen and deoxygenated blood to the heart. Blood also absorbs nutrients and waste. The cardiovascular system connects to energy as it circulates oxygen to the body's cells and also circulates nutrients. The cardiovascular system supplies oxygen and nutrients to the cells of the body and they need to generate energy and also need to produce larger molecules. Also the energy needed to pump the heart.