Structure and function of the digestive system.

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Kristy Kish  27/04/07

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.

A balanced diet is required to give the human body all the nutrients it needs to function correctly and efficiently. A balanced diet would consist of 60% carbohydrates, 20% lipids and 20% proteins. Other nutrients would be included in the food we eat and are fibre, vitamins, minerals, water and trace elements.  Energy is obtained from carbohydrates, lipids and proteins. Excess carbohydrates and lipids are stored under the skin and this can cause obesity.  Proteins are needed for growth and tissue repair.  Fibre aids the digestive system by building bulk, which is not digested but egested.  Vitamins are needed for chemical reactions within the cells and if the intake of these is too low a deficiency will occur.  

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The ingestion and mechanical breakdown of food starts in the mouth.  Your lips and tongue mix up the food with saliva and teeth break up the food into smaller pieces by grinding when you chew.  This is called mastication.  Saliva, which is released from the salivary glands, softens food making it easier to swallow.  Saliva consists of 99.5% water with 0.5% dissolved substances including mineral salts, salivary amylase, mucin and lysoeme, which is an enzyme that kills bacteria.  Salivary amylase, which is a proteins splitting enzyme, begins the process of chemical breakdown turning starch into maltase.  Swallowing is a ...

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