Circulation, Respiration and Breathing

Background Information

The body’s need for energy dictates the structure and function of two of its major organ networks, the circulatory and respiratory systems. Together they illustrate the close inter-relationship that is necessary between the various parts of the body if it is to be kept in optimum condition.

The respiratory system is comprised of the mouth and nose, the trachea (windpipe) – which itself is divided at the base into two separate bronchi (one into each lung) – and the lungs themselves. Each of these organs is carefully structured to match the work it is required to perform. For example, the nose is designed to bring air into the body through a narrow passage containing hairs and mucus that trap dirt and germs; and the lungs contain about 600 million air sacs where oxygen is brought close to the blood for absorption.

The body wants to use as little energy as possible in getting the things it needs and so it relies on a passive system of gas exchange called diffusion. Diffusion is the name given to the process whereby atoms and molecules (in this case oxygen and carbon dioxide), move from areas where they are in abundance (high concentration) to areas where they are more scarce (low concentration). You can see this process easily for yourself if you add blackcurrant juice slowly to a glass of water -–at first the colour is concentrated where it is poured in, but very soon the whole glass of water is coloured by the juice.

Getting the oxygen into the lungs though is only the beginning of the story. If the oxygen is to be used effectively it must be transported around the body to all its cells. This is where the circulatory system comes in. First described by William Harvey in 1628, human circulation is driven by a muscular pumping heart.

Heart disease is one of the biggest killers in the UK but this has not always been the case. Before the Industrial Revolution most people did manual jobs, walking was the main form of transport, and housework was heavy labour without the benefit of machines to help. Our diet has also changed dramatically. Before the Industrial Revolution, it had less high fat foods like ice cream and butter, fried food was uncommon, and no ‘convenience’ foods like hamburgers were available. The unfortunate combination of reduced exercise and a rich diet has led to a massive increase in heart disease.