Alveoli
Alveoli are tiny balloon like sacs at the ends of bronchioles. In the alveoli, exchanges in gases are made with the bloodstream. Oxygen goes into the pulmonary veins and carbon dioxide is put out of the pulmonary arteries. There are 700 million, or more, alveoli found in the lungs. Because of the large surface area of alveoli, exchanges in gases happen extremely fast.
Alveoli