The Digestive System
When we eat such things as bread, meat, and vegetables, they are not in a
form that the body can use as nourishment. Our food and drink must be changed
into smaller molecules of nutrients before they can be absorbed into the blood
and carried to cells throughout the body.
Digestion involves the mixing of food, its movement through the digestive tract,
and chemical breakdown of the large molecules of food into smaller molecules.
Digestion begins in the mouth, when we chew and swallow, and is completed in the
small intestine. The chemical process varies somewhat for different kinds of
food.
Two solid organs, the liver and the pancreas, produce digestive juices that
reach the intestine through small tubes. In addition, parts of other organ
systems (for instance, nerves and blood) play a major role in the digestive
system.
In many ways, the digestive system can be thought of as a well-run factory in
which a large number of complex tasks are performed. The three fundamental
processes that take place are:
The main part of the digestive system is the digestive tract. This is
like a long tube, some nine meters in total, through the middle of the body. It
starts at the mouth, where food and drink enter the body, and finishes at the
anus, where leftover food and wastes leave the body
How Your Digestive System Works
Mouth
Digestion of food begins in the mouth. Chewing breaks food down into smaller
particles so it can be digested. If people do not chew food thoroughly because
they eat quickly or have tooth problems, they increase the burden on the
digestive organs. Saliva contains the digestive enzyme amylase, which begins
breaking down starchy foods as soon as they enter the mouth.
Esophagus
The Esophagus, or gullet, is a muscular tube. It takes food from the throat and pushes it down through the neck, and into the stomach. It moves food by waves of muscle contraction called peristalsis.
Stomach
The stomach mechanically mixes food. It also releases substances that chemically
break down food, such as hydrochloric acid. Hydrochloric acid, often called
stomach acid, plays a key role in the stomach. It helps digest proteins, fat,
vitamins, and minerals, maintains the acidity of the stomach, and helps kill
bacteria, viruses, and parasites.
Pancreas
The pancreas, like the stomach, makes powerful digestive juices called enzymes which help to digest food further as it enters the small intestines.
Gall Bladder
This small baglike part is tucked under the liver. It stores a fluid called bile, which is made in the liver. As food from a meal arrives in the small intestine, bile flows from the gall bladder along the bile duct into the intestine. It helps to digest fatty foods and also contains wastes for removal.
Small Intestine
This part of the tract is narrow, but very long - about 20 feet. Here, more
enzymes continue the chemical attack on the food. Finally the nutrients are
small enough to pass through the lining of the small intestine, and into the
blood. They are carried away to the liver and other body parts to be processed,
stored and distributed.
Liver
Blood from the intestines flows to the liver, carrying nutrients, vitamins and
minerals, and other products from digestion. The liver is like a food-processing
factory with more than 200 different jobs. It stores some nutrients, changes
them from one form to another, and releases them into the blood according to the
activities and needs of the body.
Large Intestine
By the time food reaches the colon, most of the nutrients have already been
absorbed, leaving indigestible fiber and water. The large intestine absorbs
water, electrolytes, and a few vitamins. The length of time taken for food to
pass through the colon largely depends on fiber intake. Mucus is secreted to
protect the cells lining the colon from physical trauma and bacterial toxins.
Rectum and Anus
The end of the large intestine and the next part of the tract, the rectum, store
the feces. These are finally squeezed through a ring of muscle, the anus, and
out of the body.