journey

Digestion begins in the mouth. The grinding of food by the teeth is an example of mechanical digestion. If you chew an unsalted soda cracker, you will notice that it begins to taste sweet. Enzymes produced by the salivary glands begin to break down complex carbohydrates (starches) in the mouth. This is an example of chemical digestion.
When you swallow food, it passes into the esophagus. Rhythmic contractions of the smooth muscle of the esophagus push the food bolus downward toward the stomach. These involuntary muscle contractions are an example of peristalsis.
Mechanical digestion occurs primarily in the stomach. Proteins are decomposed into amino acids by the enzymatic action of pepsin. Hydrochloric acid in the stomach aids the pepsin. The churning of the stomach along with the chemical action of hydrochloric acid and pepsin breaks food particles down to chyme.
Digestion of proteins continues as food enters the small intestine. Enzymes produced by the pancreas mix with chyme in the small intestine. Trypsin continues the digestion of protein. Amylase continues the digestion of starch. Lipase begins the digestion of fats. Bile, which is produced in the liver and released from the gall bladder, aids in the digestion of fats. Other enzymes in the small intestine are peptidase and maltase. Peptidase digests proteins. Maltase converts sugars to glucose.
Almost all chemical digestion and absorption of nutrients takes place in the small intestine. Nutrients pass into the blood system across tiny finger-like projections in the lining of the small intestine. These structures are called villi. Villi increase the surface area of the small intestine improving the rate of nutrient absorption.
The final segment of the digestive system is the large intestine. Water is absorbed into the blood stream across the lining of the large intestine. Bacteria that live in the large intestine feed on material passing through. Some bacteria produce useful substances such as vitamin K needed for blood clotting. The bacteria found in the large intestine have developed a symbiotic relationship with humans.
Waste is compressed in the rectum and eliminated through the anus.

Starches- Foods that contain starches are usually made from flour. Some examples are bread, rolls, muffins, and cake.

Protain- Foods that contain proteins are usually from animal muscles. Some examples are hamburger, chicken, and roast beef. Gluten is a wheat protein found in foods made of wheat flour.

Fats- Fats are found in animal meat and in baked goods that contain butter, margarine and shortening. Oils are often found foods from plants, for example, corn oil, olive oil, and vegetable oil..