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Gastrointestinal Tract: Functions and Investigations

Gastrointestinal Tract: Functions and Investigations - What it is

Our gastrointestinal tract is made up of many different parts, each with its own unique function. Here is an overview of the normal functions of our gastrointestinal tract.

gastrointestinal tract functions and investigations conditions and treatments

Mouth: Apart from providing the pleasure of eating, the function of the mouth is to help in the chewing of food so that it can be broken into smaller pieces for swallowing and digestion.

Oesophagus/ gullet: The gullet is a muscular tube of approximately 25 cm in length. It delivers food into our stomachs by relaxing its muscular sphincter at lower end. It usually prevents reflux of acid from the stomach back into the gullet through contraction. In some people, this sphincter can become weakened thus allowing the free flow of acid into the gullet causing inflammation. This condition is more prone in obesity and by alcohol, nicotine and fatty food. Sufferers experience pain at the upper abdomen and heartburn.

Stomach: The stomach can be considered as a muscular sac which performs the following functions:

  • Mixing of foods ( as a blender )
  • Reservoir and gatekeeper to control for food delivery into our small bowel for digestion
  • Secretion of acid to help digestion of protein.

Small intestine: It is 1.5 metre in length with the primary function of digestion of food. Its internal surface area is increased by numerous folds in order to increase the surface area for absorption of nutrients. Protein, fat and carbohydrate molecules are broken down into smaller fragments so they can be easily transported across the small bowel wall and into the blood stream and lymphatic system. This process is called digeston. As much as 9 litre of water can be absorbed across the small bowel per day. Vitamins and minerals such as iron are also absorbed by the small bowel.

Pancreas: This is a gland that sits below the stomach. It secretes enzymes into the small bowel wall which helps in breaking down protein, fat and sugar into smaller frgaments. It also secretes the hormone insulin into our blood stream which maintains sugar level.

Gallbladder: For storage of bile made by liver. Bile salts helps to digest fat. When food bolus arrives into the small bowel, gallbladders will be stimulated to contract thus emptying bile into the small bowel to help with digestion. We can however live without our gallbladders ( as happened to people who have their gallbadders removed due to stones ) though we shall become intolerant of fatty food.

Colon (large bowel): the large bowel starts from the small bowel and ends at the rectum. The rectum is about 12 cm long and joins the anus. It absorbs up to 3 litre of water daily. Its resident bacteria population digest food components such as roughage and fibre which are not digested by the small bowel. Anal canal has muscular sphincter which controls defaecation. Entry of faeces into the rectum causes relaxation of the muscular sphincter and at the appropriate social situations, the rectum can be emptied by contraction of abdominal muscular wall and relaxation of anal sphincter.

Liver: The liver is the largest organ in the human body and performs some of the most complex functions. It receives 25% of blood supply at any one time and weighs about 1.5 kg. Its functions are:

  • Synthesis of proteins, antibody and fats.
  • With the help of insulin, it controls sugar level.
  • It detoxifies many drugs and alcohol.
  • It acts as a sieve to 'trap' bacteria that have gained access into the body through the bowel wall.

Common investigations of the gastrointestinal tract

Common investigations on the gastrointestinal tract are largely carried out with video endoscopes. Video endoscopes produce high quality picture of the internal lining of the gastrointestinal tract. The two common video endoscopy performed are oesophagogastroduodenoscopy (OGD for short; it is often also called as gastroscopy ) and colonoscopy.

Oesophagogastroduodenoscopy (OGD)

OGD is often used as the investigation if you have symptoms of indigestion, dyspepsia, heartburn, upper abdominal pain or weight loss. It allows examination of your gullet, stomach and duodenum. Small pieces of the lining of the stomach ( biopsies ) can be taken for examination under the microscopes. Biopsies can be safely taken without any pain or discomfort or bleeding unless you are on anti-coagulant. You would therefore need to inform your doctor if you are on aspirin or warfarin before the test is performed.


It is often performed on outpatient basis but you would require to be fasted overnight. Before the scope is inserted, your throat would be sprayed with local anaesthetic ( lignocaine spray ). Intravenous sedation is sometimes given for anxious patients though this would mean having a small needle inserted into your forearm vein and you would also be required to be accompanied home after the procedure. The scope is then passed through your mouth across the back of your throat into your gullet (oesophagus). The scope is then maneuvered into your stomach and duodenum. The test usually lasts for 5 to 10 minutes. It is extremely safe though it has been reported to cause complication of heart attacks in elderly patients.


This test allows visualisation of your whole large bowel and the last part of small bowel. The success rate for having a complete examination to the uppermost part of the large bowel is around 95%. Biopsies can be taken and small polyps can be removed at the time of colonoscopy. Your doctor would remove the polyps if they are found during the examination as they may lead to large bowel cancer if they are left on place after 15 to 20 years. You would not feel any pain if biopsies are taken or polyps removed.


You would be required to undergo low residue diet (avoiding vegetables, fruits, all bran products) for two days and to go on clear fluids one day before the test. On the afternoon before the test, you would be given some medicine by your doctor to purge your bowel. You would be given intravenous sedation and the instruments would be passed into your anus and maneuvered around to the uppermost part of your large bowel.

The major complications of the test are perforations and bleeding. Perforations are leak from the large bowel wall. The risk if these two complications increases if your doctors are required to remove polyps. From the medical literature, the rate of these complications occurring is about 1/1000.

Gastrointestinal Tract: Functions and Investigations - Symptoms

Gastrointestinal Tract: Functions and Investigations - How to prevent?

Gastrointestinal Tract: Functions and Investigations - Causes and Risk Factors

Gastrointestinal Tract: Functions and Investigations - Diagnosis

Gastrointestinal Tract: Functions and Investigations - Treatments

Gastrointestinal Tract: Functions and Investigations - Preparing for surgery

Gastrointestinal Tract: Functions and Investigations - Post-surgery care

The information provided is not intended as medical advice. Terms of use. Information provided by SingHealth