ABSTRACT
There are two lungs that sit in a closed compartment called the thorax. The lungs are surrounded to the lateral, anterior, posterior and superior sides by the rib cage. The diaphragm, a band of muscle tissue, provides the inferior border of the thorax. A double-layered membrane surrounds the lungs. The inner layer is the pulmonary pleura which covers the lung. This is then surrounded by the outer parietal pleura. The parietal pleura are attached to the thoracic walls so that when the thorax expands the lungs expand as well. The pulmonary capillaries contain blood from the pulmonary artery that is high in carbon dioxide content and low in oxygen content. A number of muscles form an integral part of the pulmonary system by providing part of the dynamic component required for inspiration and expiration and in some cases providing support and constraints for the thorax.
