The respiratory system allows us to breathe by taking in oxygen and removing carbon dioxide through a process of gas exchange. Air enters through the nose and mouth, then travels through the pharynx, larynx, trachea, and bronchi before reaching the lungs. In the lungs, air passes through bronchioles and into alveoli, tiny sacs where oxygen and carbon dioxide are exchanged between the lungs and bloodstream. The diaphragm and rib cage work together to inhale and exhale air during breathing.