Lungs play a major role in the respiratory system. In humans, a pair of lungs are designed in such a way that they are lined by a thin membrane, the smaller tubes called bronchioles a balloon-like structure called alveoli and network of blood capillaries increase the surface area for exchange of gases.
Humans have two lungs and are situated within the thoracic cavity of the chest. They are soft spongy and elastic organ enclosed in a thin membranous sac called the pleura. Lungs are divided into a smaller structure called bronchi which are divided into bronchioles. Alveoli are small, round or balloon-like structure found the end of the bronchioles and provide a larger surface area and maximizes the exchange of gases inside the lungs.