Human digestive system structure and function

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The human digestive system is responsible for breaking down the food we eat into simple substances which can be absorbed into the blood.

The substances thus absorbed are then utilized for building tissues and providing energy for various functions of the body.

It starts with the mouth where food is chewed so that further digestion becomes easy.

The month has glands which produce saliva. The major glands are parotid, submandibular and sublingual salivary glands.

Saliva keeps the month moist. It also has an enzyme called amylase which helps in digestion of carbohydrates. Saliva also has some antibacterial substances which keep the mouth clean.

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The tongue has receptors in taste buds which enable us to appreciate the various tastes. It also aids in swallowing food.

human digestive system

After chewing food is swallowed and enters the food pipe (esophagus-a muscular tube). The food pipe is situated immediately behind the windpipe. The windpipe can be felt in the hollow just above the breast bone in the center of the chest.

What happen if the food enters the wind pipe? This is called choking and at times it can even be fatal. Is it not a wonder that we eat so many times but yet rarely choke. How does the body prevent choking?

There is a lid like structure called epiglottis just at the entrance to the windpipe. When we swallow anything the epiglottis closes the opening of the windpipe so that food or water cannot enter the windpipe but goes into the food pipe.

Watch the video below to see the epiglottis in action.

What we eat or drink does not go down by gravity but is propelled by the muscular contraction of the esophagus.

That is why we can drink or eat while standing upside down. The food goes forward into the stomach but does not come out through the mouth.

The food pipe leads into a muscular bag like structure called stomach. This is situated in the left side of the abdominal cavity just below the diaphragm.

The juice secreted by the stomach is highly acidic. This acidic juice can destroy the stomach itself. But the stomach protects itself by coating the inner lining with a thick slimy substance called mucus.

The stomach churns the food mixing it with digestive juices to facilitate digestion and then pushes the contents into the small intestine. When the muscles of stomach contract the contents are pushed both up towards the food pipe and down into the intestine.

A valve like mechanism prevents the contents from entering the food pipe. Any defect in this valve like mechanism results in a condition called gastro-esophageal reflux disease (GERD) which results in regurgitation of food into the food pipe. This condition causes heartburn and also predisposes to bronchial asthma.

This mechanism is not fully developed in small babies. That is why babies spit up milk during the first six months.

The small intestine is a whooping 20 feet long muscular tube with a diameter of about three centimeters. During the transit in the small intestine food is fully digested and all the nutrients are absorbed. What remains undigested forms the fecal matter and is pushed into the large intestine.

In order to digest the food we eat, specialized proteins called enzymes are required. Saliva contains amylase which helps in digestion of carbohydrates and lipase which helps in fat digestion.

Liver plays an important role in the digestion of fat. Pancreas secretes several enzymes which aid in digestion of carbohydrates, proteins and fat.

The tubes carrying digestive juices from the liver and the pancreas join together and open into the first part of the small intestine called the duodenum.

The large intestine is about 5 feet long and bigger than the small intestine with a diameter of about six centimeters. It absorbs most of the water from its contents resulting in the formation of fecal matter which consists of undigested food (fiber). Fecal matter is excreted through the anus by the contraction of the large intestine.

Appendix: The large intestine in the beginning has a slightly enlarged pouch like structure called cecum. The last part of the small intestine called the ileum joins the cecum.


Just below the junction of ileum and cecum a tube like structure with a blind end protrudes from the cecum. This is called appendix. It may be absent in a few people. This does not seem to have any important function though it is believed that it may have some role in fighting infections.

Occasionally it can get infected and inflamed resulting in a condition called appendicitis.

Respect your digestive system: Man should consume only what is naturally suited for his body (Diet and Health). Consumption of excessively spicy food, cigarette smoking and alcohol cause irritation of stomach leading to gastritis and ulcer of stomach and intestine. Include fresh fruits and raw vegetables in your diet.

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Common problems of the digestive system

Gastroenteritis or diarrhea in children

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Page last reviewed on 22nd January 2011

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