Lungs: is the essential respiration organ. The two lungs are located near the backbone on either side of the heart in the chest cavity. Their main function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. This exchange of gases is accomplished in the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs called alveoli.
In the thoracic cavity, carefully separate the pericardium or sac surrounding the heart and the diaphragm from the body wall. Locate the two, spongy lungs that surround the heart. The tissue that covers and protects the lungs is called pleura.