Digestive System

Part I of Essay
The human body uses various kinds of food for energy and growth. To be used, however, food must be changed into a form that can be carried through the bloodstream. The body's process of extracting useful nutrients from food is called digestion. The of humans and other h ....

Part II of Essay
.... by the teeth. The tongue helps mix the food particles with a digestive juice called saliva, which is secreted in the mouth. Saliva moistens the food so it can be swallowed easily. It also changes some starches into simple sugars. It is important to chew food thoroughly to mix it well with saliva. Thorough chewing cuts food into small pieces that are more easily attacked by digestive juices. Food should not be washed down with quantities of liquid to avoid chewing. From the mouth the food is swallowed into a transport tube, named th ....