by Angelina Moore

Created on: June 24, 2009

The digestive system is an intricate, dexterous process in which large food molecules are lubricated and passed through glands and organs, so that they can be broken up into smaller molecules, and excreted as waste.

The digestive organs, like the stomach and intestines are tube-like and store the food as it passes through the body. The digestive system in itself is essentially one long twisting tube that stretched from the mouth to the anus.

The digestive process

The main stages of the digestive process are as follows: it begins with the mouth, then the food passes through to the stomach, then to the small intestine and then to the large intestine followed with the excretion of waste though the anus.

The beginning of the digestive process begins with the mouth, where food is lubricated, or softened, in order for it to continue though to the esophagus. As food is eaten, it gives off a smell which the salivary glands respond to and secrete saliva. Similarly the process of Mastication, where the teeth and tongue grind and gnaw food, causes glands beneath the tongue to secrete the saliva. The saliva primarily has two main functions; it lubricates, moistens and compresses food. Also saliva contains a digestive enzyme known as amylase; this breaks down carbohydrates into smaller molecules so that they can continue down the esophagus.

The esophagus is a long muscular tube and is approximately 23cm long. It is lined with a mucous membrane which is made up of epithelial cells, these secrete a lubricate fluid which assists the food on its way to the stomach. Also in the esophagus wall, there is muscle, this contracts and squeezes food down the tube towards the stomach.

In the digestive process the stomach, has three main functions. Firstly, it acts as a storage place for food and liquid, this is because the upper part of the stomach muscle relaxes and so large volumes of food and liquid can be stored here. In the lower part of the stomach the muscular walls stir up the food and mix it with gastric juices, these contain protease enzymes, to digest proteins and hydrochloric acid. This acid provides the optimum conditions for the protease enzyme, pepsin to work. Pepsin breaks down food proteins into peptides. The third task of the stomach is to release the broken down food into the small intestine.

When the food enters the small intestine the digestion process is complete. At first when the food enters the small intestine it enters the duodenum then through to the jejunum and then the ileum (the final part of the small intestine). The small intestine produces all three types of pancreatic enzymes these include proteases, amylase and lipase as well as other digestive enzymes which help to digest any leftover food. Any dissolved food is absorbed into the bloodstream here, by the process of diffusion.

The large intestine is where any food that has not been absorbed into the blood enters here. The excess water and salts remaining in the food is removed which leaves the remaining food to be turned into faeces.

At the end of the digestive process, the faeces are stored in the rectum before it is excreted from the body via the anus.

Sources

http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/

http://www.enchantedlearning.com/subjects/anatomy/di gestive/

Letts GCSE success revision guide, AQA additional science higher book.

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