I am an organ system. Smoking can damage my delicate balloon-like alveoli (air sacs), filling them with tar. The fewer alveoli are working, the less air I can take in. The less air I can take in, the less oxygen gets to the blood for use by the cells of the body. I am the ____________? A. Nervous B. Circulatory C. Respiratory D. Skeletal I am an organ system. Food enters the mouth and is chewed by the teeth; in the stomach acid breaks down the food further; many more organs process the food ensuring that nutrients from it are passed into the blood. I am the _____________________? A. Digestive B.Muscular C. Respiratory D. Circulatory ​