What's the first step in digesting food? Believe it or not, the digestive
process starts even before you put food in your mouth. It begins when you smell
something irresistible or when you see a favorite food you know will taste good.
Just by smelling that homemade apple pie or thinking about how delicious that
ice cream sundae is going to taste, you begin to salivate - and the digestive
process kicks in, preparing for that first scrumptious bite.
If it's been a while since your last meal or if you even think about
something tasty, you feel hungry. You eat until you're satisfied and then go
about your business. But for the next 20 hours or so, your digestive system is
doing its job as the food you ate travels through your body.
Food is the body's fuel source. The nutrients in food give the body's cells
the energy and other substances they need to operate. But before food can do any
of these things, it has to be digested into small pieces the body can absorb and
use.
 Almost all animals have a tube-type digestive system in
which food enters the mouth, passes through a long tube, and exits as
feces (poop) through the anus. The smooth muscle
in the walls of the tube-shaped digestive organs rhythmically and efficiently
moves the food through the system, where it is broken down into tiny absorbable
atoms and molecules. During the process of absorption, nutrients that come from
the food (including carbohydrates, proteins, fats, vitamins, and minerals) pass
through channels in the intestinal wall and into the bloodstream. The blood works to
distribute these nutrients to the rest of the body. The waste parts of food that
the body can't use are passed out of the body as feces.
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