Digestive System

The stomach churns food and adds gastric Juice, which breaks down proteins. Food exits the stomach as chyme, a thick liquid.

Bile and pancreatic juice - act on the chyme in the upper small intestine. Pancreatic juice digests proteins, fats, and sugars and starches. Bile helps break down fats.

Digested foods - are ab­sorbed into the bloodstream from the small intestine. The indigestible remains pass into the large intestine and are eliminated from the body.

Digestive system is the group of organs that break down food into smaller particles, or molecules, for use in the human body. This breakdown makes it possible for the smaller digested particles to pass through the in­testinal wall into the bloodstream. The particles are then distributed to nourish all parts of the body.

The digestive system consists primarily of the alimen­tary canal, a tube that extends from the mouth to the rec­tum. As food moves through this canal, it is ground and mixed with various digestive juices. Most of these juices contain digestive enzymes, chemicals that speed up re­actions involved in the breakdown of food. The stomach and the small intestines, which are parts of the alimen­tary canal, each produce a digestive juice. Other diges­tive juices empty into the alimentary canal from the sali­vary glands, gall bladder, and pancreas. These organs are also part of the digestive system.

The fats, proteins, and carbohydrates (starches and sugars) in foods are made up of very complex molecules and must be digested, or broken down. When digestion is completed, starches and complex sugars are broken down into simple sugars, fats are digested to fatty acids and glycerol, and proteins are digested to amino acids and peptides. Simple sugars, fatty acids and glycerol, and amino acids and peptides are the digested foods that can be absorbed into the bloodstream. Foods such as vitamins, minerals, and water do not need to be di­gested.

From mouth to stomach. Digestion begins in the mouth. Chewing is very important to good digestion for two reasons. When chewed food is ground into particles, the digestive juices can react more easily. As the food is chewed, it is moistened and mixed with saliva, which contains the enzyme ptyalin. Ptyalin changes some of the starches in the food to sugar.

After the food is swallowed, it passes through the  oesophagus into the stomach. In the stomach it is thoroughly mixed with a digestive juice by a vigorous to-and-fro churning motion. This motion is caused by contractions of strong muscles in the stomach walls

The digestive juice in the stomach is called gastric juice.  It contains hydrochloric acid and the enzyme pep sin. This juice begins the digestion of protein foods  such as meat, eggs, and milk. Starches, sugars, and fats are not digested by the gastric juice. After a meal some food remains in the stomach for two to five hours. But liquids and small particles begin to empty almost immediately. Food that has been churned, partly digested and changed to a thick liquid is called chime.  Chyme passes from the stomach into the small intestine.

In the small intestine, the digestive process is completed on the partly digested food by pancreatic juice intestinal juice, and bile. The pancreatic juice is pro­duced by the pancreas and pours into the small intertine through a tube, or duct. The pancreatic juice contains the enzymes trypsin, amylase, and lipase.  Trypsin breaks down the partly digested proteins, amylase changes starch into simple sugars, and lipase splits fats into fatty acids and glycerol. The intestinal juice is pro­duced by the walls of the small intestine. It has milder  digestive effects than the pancreatic juice, but carries out similar digestion. Bile is produced in the liver, stored in the gall bladder, and flows into the small intestine through the bile duct. Bile contains chemicals that help break down and absorb fats.

When the food is completely digested, it is absorbed, by tiny blood and lymph vessels in the walls of the small intestine. It is then carried into the circulation for nourishment of the body.

Related articles: Alimentary, Canal, Amino acid, Assimilation, Bile, Carbohydrate, Cellulose, Dyspepsia, Enzyme, Fat, Gland, Indigestion, Intestine, Liver, Lymphatic system, Mastication, Oesophagus, Pancreas, Pepsin, Starch, Stomach, Sugar, and Teeth.