The human body needs fuel to live. We eat food for fuel. But just getting the food into the body is only a small part of the process. The food must be broken down into chemicals that the body can use. This whole process is called digestion. Some of the organs involved in digestion are the mouth, esophagus, stomach, small and large intestines, gallbladder, pancreas and liver. Follow the lizards to find out how the body uses the food we eat.

1.

Mouth and Teeth

	The mouth and teeth are the first step in breaking food down. During the process of chewing, food is shredded and ground. Powerful muscles move the mandible, or lower jaw, while the food is chewed. The front teeth cut the food and the back teeth grind the food. There are three main parts to the tooth: the root, the neck and the crown. The root is the part inside the jaw. The neck is a narrow connection between the root and the crown. The crown of the tooth is above the gum. First teeth come in between 6 and 8 months. By age 6, baby teeth are gradually replaced by permanent teeth. There are 32 permanent teeth. When food is being chewed, saliva is squirted into the mouth. Saliva helps to soften the food. It contains an enzyme that helps break down the starch in the food.
	After chewing, the food is swallowed and passes down the esophagus to the stomach. The esophagus is about ten inches long. The tongue helps push the food to the back of the mouth, and the muscles in the esophagus move the food down the tube.

The horned toad's main food is ants. It often sits near an ants' nest with its mouth wide open.

2.

The stomach is a sac shaped like a "j" and is about eight inches long. In the stomach, food is mixed with acids. The muscles in the stomach move, which helps break down the food. The stomach is protected from the acid by a lining. From the stomach, the food pulp is sent to the small intestine. Food leaves the stomach a little bit at a time.

The small intestine is the final place for digestion. Measuring about twenty feet in length, the small intestine is one inch in diameter. Digestive juices released in the small intestine finish breaking down the food.

The food is moved along the small intestine in a squeezing motion known as peristalsis. This motion is much the same as squeezing a tube of toothpaste. All of this movement causes the noise when we say our stomach is "growling."

Lining the small intestine are millions of fingers called villi. These absorb the chemicals that we need from the food into the body. It is at this point the food is actually in the body.

Waste products and food that are not absorbed in the small intestine pass into the large intestine. This waste material is called feces. The large intestine is only five feet long but is larger in diameter than the small intestine. The large intestine includes the colon.

In the large intestine, feces are formed from water, undigested food and bacteria. Water is absorbed back into the body so the waste material becomes more solid as it travels through the colon. It may take as long as twenty hours for food to pass completely through the large intestine.

3.

The pancreas is an elongated gland that is below the stomach. It produces pancreatic juice that contains digestive enzymes. The pancreas also secrets insulin into the blood. Insulin is needed to allow glucose or sugar from food to get into the bloodstream. People who cannot produce insulin are diabetics.

The largest gland in the body is the liver. It is on the right side of the body underneath the ribs. It weighs about three pounds and is eight inches long. The liver stores a form of glucose called glycogen. Vitamin A is manufactured in the liver. Bile which is needed to breakdown fat, is made in the liver. This organ is also where alcohol, drugs, bacteria and old blood cells are broken down and removed from the body. Damage to the liver can be serious because this organ is extremely necessary to life.

The gallbladder is a small sac on the underside of the right lobe of the liver. It stores bile that is made by the liver. Bile travels from the liver through the hepatic ducts to the gallbladder. It holds about two ounces of bile. Bile is needed to breakdown the fat that is in food.