Gastrointestinal anatomy and physiology, Part 1

Introduction

The functions of the digestive system can be summarised as ingestion, digestion, absorption and elimination. Ingestion refers to taking food and water into the body, the processes of eating and drinking. Ingested food molecules are often large and insoluble; in order for them to be absorbed into the body they must first be broken down into smaller units. The process of converting large, ingested food molecules into a form which may be absorbed is termed digestion. After food has been digested it must then be absorbed into the blood or lymphatic systems of the body before it can be utilised. The process whereby digested food is transferred from the lumen of the gut into the circulatory systems is called absorption. Not all ingested material is absorbed, some continues along the length of the digestive tract and is eliminated as waste. Fibre is not broken down by any digestive processes and is eliminated in the same form it was eaten. Water is absorbed unaltered into the blood.

Structures of the digestive system

Essentially, the gastrointestinal (GI) tract or gut is a single tube which runs from the mouth to the anus. The old fashioned name for the GI tract is the alimentary canal. The digestive system consists of the organs which compose the GI tract and the accessory organs of digestion. These accessory organs are not part of the tract but produce and secrete fluids and enzymes essential for the digestive process. Different sections of the GI tract have different properties and diameters of lumen, which allow for the specific functions necessary.

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