6. Mechanisms of work related disease
The respiratory system is essential to life as the body's provider of oxygen. Oxygen is provided in a way which the body can use, cleaned, warmed and humidified, ready for delivery to cells to permit aerobic metabolism. The respiratory system also allows for the excretion of carbon dioxide. The respiratory system is usually considered to comprise: airways (nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles); an area of gas exchange (alveoli); and the necessary structures to drive and control respiration (ribs, intercostals muscles, diaphragm, pleura and nervous system).
The respiratory system is also important as one of the bodies significant interfaces with the environment. A normal person usually breathes about six litres of air a minute, and during exercise this may increase to over 75 litres per minute. The alveoli where gas exchange occurs are necessarily in intimate contact with respired air, and have a large surface area to facilitate gas exchange. Consequently, the respiratory system is one of the areas of the body with greatest exposure to the environment and one of the first to show the effects of many environmental insults.
The upper part of the respiratory system comprises nasal passages, sinuses, pharynx, and larynx down to the level of the epiglottis. At rest most individuals breathe preferentially through their nose, the mouth being used for breathing during periods of exercise when higher volumes are inhaled. These upper airways are a series of irregular or rounded cavities and tubes lined with a ˜mucosa' which has a rich blood supply. Air flow through them tends to be relatively rapid and turbulent. Air is very effectively warmed and humidified as it passes through this area.
Once inhaled air passes the epiglottis it enters the ˜tracheobronchial' region. The trachea is a muscular tube with ˜U' shaped cartilaginous rings incomplete posterio