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The Digestive System
Coachbook pgs. 67-68
Name: ____________________________
Getting the Idea: The nutrients your cells use to produce energy comes from the food you eat.
Breaking food down for energy also produces wastes. Those wastes must be removed from the
body. Two of your body systems break food down into usable forms and remove wastes
products from your body.
The Digestive System: the digestive system is the group of organs that break food down into
molecules that are small enough to be absorbed by and transported throughout the body.
The Digestive System
Digestion begins in the mouth as your teeth grind, crush, and break apart your food. Breaking
food into smaller pieces is known as mechanical digestion.
As you chew your food, your tongue moves the food around and mixes it with saliva. Saliva
moistens the food so it is easier to swallow. Saliva also contains an enzyme that begins to break
down starches and sugars. An enzyme is a protein that speeds up a chemical reaction.
When food has been chewed enough, it is moved to the back of the mouth for swallowing.
After food is swallowed, it passes the epiglottis, a flap of tissue that covers the opening of the
trachea to keep food out. The food then moves into the esophagus. The esophagus is a
muscular tube that connects the mouth to the stomach. Contractions of the muscles in the wall
of the esophagus push the food toward the stomach. These contractions are called peristalsis.
The stomach is a muscular organ. It continues mechanical digestion by contracting and
squeezing its contents. Glands in the stomach produce enzymes and acids that continue to
break food molecules apart through chemical digestion.
Food remains in the stomach for several hours. The stomach digests the food into a liquid. This
liquid then enters the small intestine, a long, muscular tube where the body absorbs nutrients
from food.
The pancreas is a gland that releases digestive enzymes and other chemicals into the small
intestine. Some of these substances neutralize stomach acids, which would otherwise damage
the lining of the intestine and prevent enzymes from doing their job. The liver also helps with
digestion in the small intestine. The liver is an organ that makes bile, a liquid that helps to break
down fat. The bile produced by the liver is temporarily stored in the gall bladder.
Once food is digested, nutrients are absorbed through the walls of the small intestine. The walls
of the small intestine have many folds called villi, which increase the surface area that can
absorb digested food. Nutrients enter the bloodstream through the capillaries in the villi. The
blood then transports the nutrients to all the cells of the body. Any undigested material left in
the small intestine is moved by peristalsis into the large intestine. Peristalsis is waves of muscle
contractions that pushes food through the digestive tract. The large intestine is an organ of
both the digestive system and the excretory system. Its role in digestion is to absorb water from
the undigested material. The large intestine also compacts the solid wastes that remain from
undigested food.
The remaining material is ready for elimination from the body. The rectum- a short tube that is
the last portion of the large intestine. Waste material is pressed into a solid form. Waste
material exits through the anus, a muscular opening at the end of the rectum.