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The functions of the human digestive system


Major functions of the human digestive system can be summarized into:

1. Digestion
2. Absorption
3. Excretion
4. Protection

A series of organ spreading from mouth to anus has a distinctive role in achieving these functions. A major responsibility of stomach and small intestine is digestion and absorption, a process which needs both chemical and physical mechanisms. The large intestine is majorly involved in absorption of water associated with desiccation and compaction of waste. Sigmoid colon and rectum are associated with storage prior to elimination of waste.

To gain these benefits, one of the major factors is the motility of the digestive tract especially stomach and small intestine which helps to do every part of the digestive system its job1

The human digestive system has its own specialized nervous system known as Enteric Nervous System which is capable of doing work independently from the Central Nervous System. Major functions of the enteric nervous system are:

1. Modulating secretions of gastrointestinal tract
2. Motility of gastrointestinal tract
3. The immune and inflammatory response of gastrointestinal tract2

The time taken for the food to transit through the gastrointestinal tract depends on many different factors but roughly 50% of the stomach empties into the intestine within half an hour and complete stomach empties in about 2 hours34.

Gastrointestinal tract also plays an important part in the immune system of the body. The large surface area of the gastrointestinal tract provides protection against the harmful bacteria and pathogens. There is an extensive immune system in the gut named as Gut Associated Lymphoid Tissue (GALT) which keeps the microorganisms away from entering the circulation of the body. A pivotal component of this protection is the mucosal barrier which acts in the physical, chemical and immunological way against the microorganisms5

Low pH of the stomach also plays important role in fighting against the microorganisms. Stomach pH ranges from 1-4 which not only helps in digesting the food but also kills all the microorganisms which get the chance of entering the GIT6

The intestine harbors a group of human-friendly bacteria which help to deal with the molecules that otherwise cannot be broken down. Moreover, these human-friendly bacteria check the growth of harmful bacteria because both have to compete for limited resources within the intestine.

There are some enzymes in the human intestine which not only do detoxification of antigens but also help to metabolize the drugs. The gastrointestinal tract processes the drugs by several mechanisms to change the structure of the drug making it more familiar with body and thus there are less chances of those drugs to be considered as foreign body which protect them from being targeted by the immune system. It means the human digestive system and the gastrointestinal tract facilitates the drug for performing its function.8

Besides maintaining the blood glucose level, the pancreas secretes a juice of digestive enzymes which break down the food particles into digestible components. Pancreas usually secretes 1.5 to 2 litres of digestive juice daily9

Writer: Dr. Owais Amin


Topics: Gastrointestinal tract

Horea Piper

Written by Horea Piper