Lungs are the pair of respiratory organs situated in the thoracic cavity on the either side of the heart. The lungs are enclosed by a serous membrane called pleura. The are spongy in texture and are highly elastic. They compress and expand by the movement of rib cage and diaphragm during breathing. They communicate with the atmosphere through trachea which opens into the pharynx. The lungs are divided into lobes-right lung has three lobes viz, upper lobe, middle lobe and lower lobe. The left lung has only two lobes viz, upper and lower lobe.