The human body has two lungs—both divided into lobes: the left has two lobes, and the right has three lobes. As a person breathes, the air travels down the windpipe, eventually branching out into the mucus-lined bronchi; from there, the bronchi split into tens of thousands of even smaller tubes called bronchioles that connect to tiny sacs called alveoli. The number of airways in the average human is immense, with both lungs containing about 1,500 miles (2,400 kilometers) of airways, with a total surface area of about the size of a tennis court, plus about 300 to 500 alveoli. The lung capacity changes depending on several factors, too—for example, females usually have 20 to 25 percent lower capacity than human males, and logically, taller people have more capacity than shorter people. And if you have lived at sea level all your life, your lung capacity is probably less than a person who has lived in a high-mountain region all their life (because the mountain air is thinner and has less oxygen, the body compensates by expanding the capacity of the lungs and thus, takes in more oxygen).