Pneumothorax (collapsed lung)

The lungs sit in the chest, inside the ribcage. They are covered with a thin membrane called the "pleura." The windpipe (or trachea) branches into smaller airways. In this drawing, 1 lung is normal, and 1 has collapsed because air has leaked out of it. The air that has leaked out of the lung (shown in blue) has filled the space outside of the lung.