Big+Idea+7

__Big Idea 7__ Alveoli and villi

__Alveoli__Alveoli are in the lungs. They are little sacs capable of holding air. They are surrounded by capillaries that carry blood. The capillaries carry oxygen poor blood to the alveoli, where the special membrane allows the diffusion of oxygen into the lungs and carbon dioxide out of the blood. Each human lung contains about 150 million alveoli. The alveoli allows the surface area of the lungs to increase, thus allowing more oxygen to enter the blood stream and carbon dioxide and other wastes to pass out more quickly. There are 3 different types of alveolus cells

Squamous Alveolar: Form the wall of the alveolus Great Alveolar: Secrets pulmonary surfacant, which lowers the surface tension of water and allows the membrane to separate, thus allowing greater capability to exchange gasses through the form of diffusion. Surfacant is constantly released through exocytosis. Macrophages: Large particles that destroy foreign and unwanted material.

The second primary purpose of the surfacant is to allow reinflation of the alveoli easier when inhaling. The great alveolar also repairs parts of the alveoli when some portions are damaged or are otherwise rendered incapable of operating normally.

__Intestinal Villus__ Villi are tiny, finger-like projections on the interior of the small intestine. On the villi are even smaller projections called microvilli. The purpose of such things are to increase the surface area of the intestine, thus allowing more efficient absorption of nutrients and other nessicary materials found in food that are required in the body. It also helps by allowing diffusion to occur, since if the process was considerably slower, the concentration of nutrients in the blood and food would be equal, thus nutrients wouldn't be absorbed. Capillaries line the interior of the villi, and are the main means of getting nutrients from the food in the intestines to the rest of the body.

__Comparison__ Both villi and alveoli increase the surface area of their respective organs. The increase in the surface area allows said organs to operate more efficiently. The villi only allow diffusion of materials into the blood stream, while the alveoli allow diffusion of gas into the blood stream and wastes out of the blood stream.