Gas exchange of oxygen and carbon dioxide takes place in the alveoli<span>. Oxygen from the inhaled air diffuses through the walls of the </span>alveoli<span> and adjacent capillaries into the red blood cells. The oxygen is then carried by the blood to the body tissues.</span>
This qualifying core is an area with a population density of at least 1,000 people per square mile that contains at least 50 percent of Page 8 12-8 Urban and Rural Classifications the place's total population and is contiguous with other qualifying urbanized territory that also meets the population density criterion.
