The gastrointestinal tract has three major functions, digestion, absorption, and defecation. Digestion is the break down of food into small molecules. Absorption is the extraction of those molecules into the blood. Defecation is the removal of waste out of the GI tract.

Absorption mainly occurs in the small intestine and, by certain extent, the large intestine. Digestion occurs from mouth to the end of small intestine.

As nutrient is concerned, GI tract failure downstream of the stomach will impede absorption; GI tract failure upstream of the large intestine will impede digestion, and, in turn, absorption.

Therefore, if GI tract failure occurs, we will invariable absorb less nutrient, either from improperly broken down food or the inability of absorbing them at all.

It depends on which area of the GI tract fails. There’s the pharynx (pronounced FAIR inks) where the chewing, moistening, and a little chemical breakdown of starch happens. Then there’s the esophagus that transports the food to the stomach. The stomach is mostly for mixing and storage, plus chemically breaking down proteins. The acid in the stomach also helps kill germs and break down some foods. Nothing gets absorbed in the stomach except alcohol and aspirin.

The absorption of nutrients mostly takes place in the small intestine. The gall bladder squirts in some bile from the liver to help break up fats. The pancreas squirts in more enzymes for chemically breaking down fats, carbohydrates, and proteins. When the nutrients are broken down far enough, they are absorbed by the blood that travels in the walls of the small intestine. (From there, the blood goes to the liver for filtering, then back to the heart to be circulated.)

Anything that wasn’t absorbed in the small intestine moves on to the large intestine. A lot of water is absorbed here, but not a lot of nutrients. So anything not absorbed already leaves the body as feces, along with all the undigested material (fiber).

If a person has damage to their mouth, a liquid diet may work for them. A person who can’t chew or swallow may be fed by a tube that goes directly to the stomach. They can still absorb nutrients in the small intestine. But if the small intestine is damaged, a person can’t absorb as many nutrients from their food. Damage to the large intestine may cause diarrhea or constipation, depending on the type of damage, but they could still absorb nutrients.

What do you think happens of the duct (tube) between the pancreas and small intestine is blocked?

It depends on what part of the tract fails and in what way, but the ultimate result is that you would not be able to digest food and incorporate the nutrients into your blood.

Food is broken down in stages throughout the digestive process, beginning with saliva in the mouth. In the stomach, acid and enzymes begin to break the food down. Once the food passes into the small intestine, it is further broken down with the help from the pancreas, liver, and gallbladder. Most of the nutrients from the food are absorbed by the small intestine. The large intestine mainly absorbs water.

Depending on which part of the gastrointestinal tract fails, the body may not be able to absorb certain nutrients as well, or at all. If nutrients aren’t absorbed, they will pass through the body with other undigested waste. Some failures are more serious than others. The gallbladder stores bile that helps break down food, but it can be removed without much effect on the digestive system. Some parts of the system, like the small intestine, are necessary to digest food, and the body cannot function without them.

Source: National Institute of Diabetes and , Digestive and Kidney Diseases.