The document summarizes the key structures and functions of the respiratory system. It discusses how air passes through the nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles to reach the alveoli in the lungs. The alveoli are where oxygen and carbon dioxide are exchanged between the air and blood through diffusion. Oxygen is then transported to cells by blood for cellular respiration to produce energy, while carbon dioxide is carried back to the lungs to be exhaled. Breathing is controlled by the diaphragm and rib muscles to inhale and exhale air, regulated by the medulla oblongata in response to carbon dioxide levels.