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Structure and function of the digestive system.

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Introduction

STRUCTURE AND FUNCTION OF THE DIGESTIVE SYSTEM The function of the digestive system is to break down large molecules in food, such as protein and starch, into monomers that can easily be absorbed into the body and with a balanced diet it does its job efficiently. The alimentary canal is a long coiled tube that runs through the body from the mouth to the anus. It consists of associated glands, the salivary glands, the liver and the pancreas. This muscular tube is organised into several distinct regions. The overall process of nutrition can be divided into several stages. Ingestion is taking in food. Humans put food into the mouth where it is chewed. Swallowing takes it down through the oesophagus and into the stomach. Peristalsis, rhythmic contractions of the gut wall, propels the food through the alimentary canal. Mechanical breakdown is how food is broken down into smaller pieces by chewing in the mouth and the churning action of the stomach. Digestion is the complex breakdown of foods such as carbohydrates, lipids and proteins into simpler molecules. Absorption is where simple food molecules pass into he blood stream in forms such as amino acids, fatty acids, vitamins, minerals, sugars and water. Egestion is where undigested food is eliminated from the body via the act of defecation. ...read more.

Middle

The stomach has deep ridges called rugae. Food is mixed and churned with gastric juices by muscular action and is retained there giving enzymes time to act. Chemical breakdown also continues in the stomach, which is a muscular sac under the diaphragm. Food stays in the stomach for as long as 40 minutes and fatty meals remain there longer. Specialised groups of cells in the gastric pits in the mucosa secrete gastric juices. Each type of cell here produces a specific secretion. Oxyntic cells secrete a solution of hydrochloric acid, which brings the pH of the gastric juice down to between 2.0 and 3.0. This is the optimum pH for pepsin and rennin. Hydrochloric acid denatures protein and softens tough connective tissue in meat, it is also a strong bactericide. Zymogen cells (peptic cells) secrete the enzyme pepsinogen, which is later converted to pepsin the enzyme that digests protein. Digesting protein is one of the main functions of the stomach. Pepsin breaks peptide bonds in the middles of the protein chain, which turns protein molecules into polypeptides. This process is complete when exopeptidase enzymes remove amino acids from the ends of the polypeptides. Mucous cells secrete the mucous that protects the stomach lining from digestive action of its own secretion. ...read more.

Conclusion

Each structure of the alimentary canal has a particular function that being the ingestion, mechanical breakdown, digestion, absorption or egestion of food. Each structure relates to the one before and the one after and a balanced diet is necessary for this efficiency. The mouth is a hard cavity containing teeth and the tongue, which efficiently breaks down food into a suitable state to travel through the oesophagus. The oesophagus, which is a rigid tube with a smooth surface, pushes the food to the stomach. The stomach, a muscular sac, aids in the mechanical breakdown of food. Cells in the gastric pits of the stomach aid in the chemical breakdown of food. This result is liquidation of the food in preparation for the small intestine. The small intestine is the longest section of the alimentary canal and here the most part of chemical digestion and absorption takes place. This moves the food to the large intestine. These are the final stages of digestion where the food is being prepared for egestion. The last minerals and water are taken here in this tube which is about 1.5 meters long. Finally the food is passed though the rectum and the anus, which are concerned with the compaction of faeces and the act of defecation. Kristy Kish 27/04/07 ...read more.

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