The human digestive system consists of a series of hollow organs that are joined in a long, twisting pipe from the mouth to the anus. The pipe is line with a thin layer of tissue called the mucosa. The job of the mucosa is to use its small glands to excrete juices that digest food.

The liver and the pancreas also excrete juices that flow into the intestine through small tubes to aid the digestive process. Blood and nerves also play an important part in the digestion of food.

The Importance of Digestion

When we eat, food is not in a form that will nourish our body. Both food and drink have to be broken down into minuscule molecules before they can be absorbed by the blood and carried to body cells. The process of breaking down food and drink into these molecules is called digestion. Nourishment is then used by our body to build and nourish cells, which provide our body with energy.

Food Digestion

Digestion is the mixing of food, the breaking down of the large molecules into minute molecules and the movement through the digestive system. As soon as we chew and swallow food, the process of digestion begins and is later completed in the small intestine. The chemical process of digestion varies slightly for different types of food.

Through the Digestive System

The hollow organs found in the digestive tract include muscles that allow the walls to expand and contract. This propels the food and liquid that we ingest through the digestive tract. Movement of the stomach, intestines and esophagus is called peristalsis. This process is very similar to the action of an ocean wave. The muscle of the organ contracts and propels digested food through the organ.

The first important muscle movement occurs when we swallow. Though we can initiate swallowing, it then becomes a voluntary action and is controlled by nerves. The swallowed food or liquid travels to the esophagus and into the stomach through a ring-shaped valve, which opens when food or liquid approaches. Once food or liquid is passed into the stomach, the valve voluntarily closes. If it doesn’t a condition known as Acid Reflux Syndrome is present and must be cared for by a health care professional.

The Stomach

The stomach has three tasks to perform once the food or liquid has passed into it. The first task is to store all swallowed food and liquid, which requires upper stomach muscles to relax enough to accept large amounts of ingest material. The stomach’s second task is to secrete digestive juices to mix with the swallowed food and liquid by using muscle movement. The stomach’s third and final task is to empty this process mixture into the small intestine.

The type of food and liquid ingested can affect the emptying of the stomach’s contents into the small intestine. These factors are fat, protein and muscle action.

Small Intestine

Once the stomach’s contents have reached the small intestine, the food is digested and dissolved by juices from the intestine, liver and pancreas. Muscles of the small intestine contract to move the digestive process along.

Once that all nutrients have been removed from the food and absorbed by the intestinal walls, there is nothing left but waste product. This includes old cells that have left the mucosa and undigested food particles known as fiber. Muscles move the waste product into the colon where it remains for one to two days before being ejected from the body in the form of a bowel movement.

Producing Digestive Juices

The first digestive juices are produced in the mouth by the salivary glands. The saliva that is produced contains enzymes that digest starch from ingested food into minuscule molecules.

The next set of digestive glands is found in the stomach lining, which produces stomach acid and an enzyme that digests ingested protein. This is a mysterious process, as researchers have not yet determined why stomach acid doesn’t eat through the stomach lining.

Once the stomach empties its contents into the small intestine, the digestive juices of two organs combine to help the digestive process along.

The pancreas is one of these organs. It secretes juices that break down the carbohydrates, fat and protein from ingested food. Other enzymes come from the gland in the wall of the small intestine to aid in the process of digestion.

The other organ that aids digestion is the liver. It produces a digestive juice known as bile, which is stored in the gallbladder. When we eat, the gallbladder sends bile to the intestine where it mixes with ingested fat. The bile works to dissolve the fat into a watery liquid. Bile works much the same as dishwashing detergent when it dissolves grease from our dishes.

After the fat has been broken down by the bile, it is digested by enzymes from the small intestine’s lining and the pancreas.

Absorbing and Transporting Nutrients

Digested water, minerals and molecules of food are then absorbed from the cavity in the upper portion of the small intestine. Most of these molecules then cross the mucosa into the bloodstream, which carries them throughout the body where they are stored until needed.

Protein

Proteins consist of large molecules that have to be digested by enzymes before they build and repair tissues throughout the body. Enzymes in stomach acid begin the process of digesting protein. This process is completed when the protein enters the small intestine. Here, enzymes from the intestinal lining and from the pancreas break the large protein molecules into amino acid, which is absorbed into the blood and carried throughout the body to build parts of body cells, including cell walls.

Carbohydrates

Total daily calorie intake is recommended to be 55 to 65 percent carbohydrates. Carbohydrates are found in such foods as breads, legumes, pasta, potatoes, rice, fruits and vegetables. These foods contain both fiber and starch. Carbohydrates are broken down into small molecules by saliva and pancreatic juices by the lining of the small intestine. Saliva and pancreatic juices break starch into molecules call maltose. Then, the juices in the small intestine transforms the maltose into glucose molecules that are absorbed by the blood. Glucose moves through the bloodstream to the liver. Here, it is stored and used when the body requires energy.

Table sugar is also a carbohydrate and it has to be digested in order to be used by the body. Table sugar is digested by an enzyme in the small intestine, which turns the sugar into fructose and glucose. These are then absorbed from the cavity in the intestine into the bloodstream.

Another type of glucose is lactose, which is found in milk and milk products. It is broken down into digestible molecules by the enzyme lactase, which can be found in the lining of the small intestine. People who are lactose intolerant are unable to produce enough lactase to digest milk and milk products.

Vitamins

Vitamins from food are a vital part of our food supply. Vitamins are absorbed by the small intestine.

Fats

Fat molecules are the source from which our bodies draw energy. Fats are broken down into a watery fluid of the intestinal cavity. The liver then produces bile that acts as a natural detergent to dissolve fat. This allows enzymes to break large fat molecules into smaller molecules, including cholesterol and fatty acids. Bile then combines with these and moves them into cells of the mucosa where they are formed into large molecules that pass into vessels called lymphatics, located near the small intestine. The small vessels carry the converted fat to the veins of the chest while blood moves fat to storage areas throughout the body.

Control of the Digestive Process

The digestive system is a fascinating part of the human body. Not only does it convert food, but it contains its own regulators. The hormones that control the digestive tract are produced and released by the mucosa in the small intestine and stomach. These are then released into the blood of the digestive system, and then to the heart, through the arteries and back to the digestive system. Hormones that control the digestive tract are cholecyslokinin (CCK,) gastrin and secretin.

CCK

CCK aids the pancreas in growth and in the production of pancreatic juices. It also aids in emptying the gallbladder.

Gastrin

This hormone aids the production of acids that dissolve and digest certain foods. It is necessary for healthy growth of the colon, the stomach lining and the lining of the small intestine.

Secretin

Secretin aids the pancreas in sending out digestive juices that are rich in bicarbonate. It helps the stomach produce pepsin, which is an enzyme that our body uses to digest protein. Secretin stimulates the liver and causes it to produce bile.

Appetite Hormones

Additional body hormones found in the digestive tract regulates are appetite. They are Ghrelin and Peptide YY.

Ghrelin

Ghrelin is produced in the upper intestine and stomach when there is no food in the digestive tract. Ghrelin is the hormone that stimulates our sense of hunger.

Peptide YY

The hormone Peptide YY is produced in the GI tract. Peptide YY quells appetite. Both Ghrelin and Peptide YY send messages to the brain that regulates our appetite, telling us when we are hungry and when we are not.

Nerve Regulators

 There are two different types of nerves that help to control our digestive system. Outside nerves lead from the unconscious part of our brain to the digestive organs. They release acetylcholine and adrenaline. Acetylcholine stimulates the digestive organs and aids in processing food and liquid through the digestive system. It also aids the pancreas and stomach in the production of digestive juices. Adrenaline aids stomach and intestine muscles to decrease blood flow to these organs.

The intrinsic or inside nerves make up a dense network in the walls of the colon, esophagus, small intestine and stomach. These nerves are triggered when the walls of the hollow organs are stretched by ingested food. It is the intrinsic nerves which release substances that regulate the speed of food movement and the digestive tract’s production of juices.

Function of the Digestive System

When the digestive system is working well, we are at optimum health. However, if it isn’t working well it can cause a wide variety of problems including diarrhea, acid reflux, constipation, vomiting, ulcers and more. If you experience any of these symptoms or stomach pain on an ongoing basis, be sure to consult a health care professional. They will be able to diagnose the problem and treat it properly so you will continue to experience good health.