Digestion involves the mixing of food, it passes through the digestive tract and the chemical breakdown of large molecules into smaller molecules. It begins in the mouth when you chew and eat, and ends in the small intestine.
Passage of food through the digestive system

The large, hollow organs of the digestive tract have a muscular layer that enables their walls to move. The movement of these walls can propel food and liquid, and mix the contents within each organ. Food passes from one body to another by muscular movement called peristalsis. The action of peristalsis looks like that of an ocean wave moving through the muscle. The body muscle contracts and then move slowly narrowing the portion owed to the lower body. These waves of alternating contraction and relaxation are pushing food and fluids through each organ.

The first major muscle movement occurs when we ingest food or liquids. Although eating is part of a voluntary process begins as it becomes involuntary and is placed under the control of nerves.

Foods to eat just go to the next organ is the esophagus, which connects the throat to the stomach. At the junction of the esophagus and stomach is a ring-shaped valve called pyloric valve that closes the passage between the two bodies. However, as food nears the closed ring, the surrounding muscles relax and allow the passage to the stomach.

The stomach must perform three mechanical tasks. First, you should store food and fluid intake. For this, the muscle of the upper stomach should relax and accept large volumes of ingested material. The second task is to mix the food, liquids and digestive juice produced by the stomach. The muscular action of the lower stomach is responsible for this. The third task of the stomach is empty its contents slowly into the small intestine.

Several factors affect the process of emptying the stomach as the food type and degree of muscular activity of the stomach and small intestine. Carbohydrates, for example, are those who spend the least amount of time in the stomach, while proteins remain longer, and fats are those that spend the most amount of time. As food is digested in the small intestine and dissolved into the juices from the pancreas, liver and intestine, bowel contents will move to facilitate mixing and subsequent digestion.

Finally, all digested nutrients are absorbed through the intestinal walls and transported throughout the body. Waste products of this process include undigested parts of food, known as fiber, and older cells that have detached from the mucosa. These materials are propelled into the colon, where they remain until the feces are expelled during the deposition.
The production of digestive juices

The digestive glands that act first are the salivary glands of the mouth. The glands that produce saliva contains an enzyme that begins to digest the starch from food and converts it into smaller molecules. An enzyme is a substance that speeds up chemical reactions in the body.

The next set of digestive glands is in the membrane lining the stomach. They produce acid and an enzyme that digests proteins. A thick mucus layer lining the mucosa and prevents the action of acidic digestive juices dissolve the stomach tissue. In most people, the stomach mucosa can resist the juice, unlike food and other body tissues.

After the stomach empties the food and juice in the small intestine, the juices of two other bodies are mixed with food to continue the process. One such organ is the pancreas, whose juice contains a large number of enzymes that break down carbohydrates, fats and proteins in food. Other enzymes that participate actively in the process come from glands in the intestinal wall.

The second organ, the liver produces bile, another digestive juice. Bile is stored in the gallbladder between meals. When we eat, bile leaves the gallbladder through the bile ducts into the intestine and is mixed with fats from food. The bile acids dissolve fat in water content of the gut, almost as detergents that dissolve grease from a frying pan. After dissolving fats, enzymes from the pancreas and intestinal mucosa digest.
Absorption and transport of nutrients

Most digested molecules of food, and water and minerals from the diet are absorbed through the small intestine. The mucosa of the small intestine contains many folds covered with tiny projections called villi. These in turn are covered with microscopic projections called microvilli. These structures create a wide area through which to absorb nutrients. There are specialized cells that allow absorbed materials cross the mucosa and into the bloodstream, which distributes them to other parts of the body for storage or to pass through other chemical modifications. This part of the process varies for different types of nutrients.



Fiber can not be digested and passes through the digestive tract without being transformed by the enzymes. Many foods contain soluble and insoluble fiber. Soluble fiber dissolves easily in water and takes a soft texture, a gel in the intestine. Insoluble fiber, however, passes through the intestines almost unchanged.

Protein. Foods like meat, eggs and beans consist of large protein molecules to be digested by enzymes before they can be used to produce and repair body tissues. An enzyme of gastric juice begins the digestion of proteins we eat. The process culminates in the small intestine. There, several enzymes of pancreatic juice and intestinal mucosa of the large molecules decompose in a much smaller, called amino acids. These can be absorbed in the small intestine and enter the blood, which leads to all parts of the body to produce cell walls and other components of cells.

Fat. Fat molecules are a major source of energy for the body. The first step in digestion of a fat such as butter is to dissolve in water content of the intestine. The bile acids produced by the liver dissolve fat in very small droplets and allow pancreatic and intestinal enzymes to break down its large molecules into smaller molecules. Some of these are fatty acids and cholesterol. Bile acids bind to fatty acids and cholesterol and help them pass into the mucosal cells. In these cells, small molecules, large molecules re-form, most of which pass to the lymph vessels near the intestine. These vessels carry the modified fat to the veins of the chest and the blood carries them to storage sites in different parts of the body.