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Food & Digestion What you should know.
In this section we learn all about the human digestion system. What happens to the food as it passes from your mouth and through to your bot! We also study the teeth and food and diet. The main food types are :- fats, proteins, carbohydrates (sugar & starch), fibre, water, vitamins and minerals. They are all important for different reasons i.e. fats are an energy store, proteins are needed for cell growth and repair, and carbohydrates are used for energy. Vitamins and minerals are only needed in very little amounts but are really important to help all the chemical reactions that go on in your body. Iron is needed for the haemoglobin in your blood and calcium for your teeth and bones. Fibre gives bulk to your food and helps clean the digestive tract and scrapes away dead cells. Different foods contain different food types. Proteins are found in meats, fish and dairy products; fats are found in butter, oils and meat; carbohydrates are found in bread, sugar, cakes; vitamins, minerals and fibre in fresh fruit and vegetables. Obviously this is only a general guide. A good diet should contain all these food groups in a good balance. What happens to our food when we eat it? Food enters our mouth and is immediately chewed into smaller pieces by our teeth. They grind, tear and chew the food into smaller pieces and the food gets covered in saliva (spit to you!). The saliva has two main purposes. It contains enzymes that 'cut' large food molecules into smaller ones. We can see this happening as starch (a big molecule) is cut into sugar (a small molecule) by the enzymes in our saliva as we chew bread. Remember that it tastes sweet after we have chewed it for a while! The saliva also helps the food slide easily down the oesophagus (gullet) as it travels by peristalsis (look it up!) to our stomach. Once in the stomach the food is bombarded with very strong hydrochloric acid (ever noticed how sick burns when you are vomiting? Well that is why!). The acid kills any bacteria on the food and starts breaking down the food too. Next the acid mixture is neutralised by bile as it passes into the small intestine. Here digestion is completed as the large molecules are all broken down into smaller ones so that they can pass through the walls of the intestine and into the blood to be pumped around the body in the blood. What is left of the food is passed along to the large intestine and any excess water is absorbed back into the body here. When you have diahorrea the food passes so quickly that this stage doesn't happen and that is why your poo is runny and you can get dehydrated! The food (which is now poo) passes into the rectum where it is stored until you go to the toilet and it passes out the anus. Yes I know it sound gross but we all do it! You can analyse a meal at 'The Nutrition Café' http://www.exhibits.pacsci.org/nutrition/default.html. Then you can play nutrient sleuths to work out what people are deficient in, and then try a quiz to test your food knowledge. The 'Interactive Food Pyramid' at http://www.nal.usda.gov:8001/py/pmap.htm is divided up into the major food groups. You can try each food group to find out how much you should eat in a day. A further link to explore is www.nutrition.org.uk More sites to help you:- http://learn.co.uk/default.asp?WCI=Unit&WCU=4531 http://www.howstuffworks.com/food.htm?printable=1 Peristalsis is the rippling movements of the muscles to help the food travel along different parts of the alimentary canal. Goblet cells protect the living cells of the alimentary canal from hard rough food and enzymes. They make mucus. The mucus covers the inside of the alimentary canal with a slimy layer over which undigested food can easily glide. Also enzymes cannot get at living cells and harm them. Sphincter muscles are what control the outlet and inlet of food from the stomach to prevent blockages. They are rings of muscle, which can contract to squeeze the tube in and out of the stomach closed so that food stays inside the stomach while it is churned up with enzymes and hydrochloric acid. Sphincter muscles are found at both ends of the stomach; where the esophagus enters the stomach and where the duodenum leaves the stomach. There is also the anal sphincter at the end of the alimentary canal, which opens to let faeces pass out of the rectum. Features which makes it the ileum good at absorbing
digested food are: It is one of the narrowest parts of the alimentary canal so food is always quite near the walls making it easier for food molecules to pass through the walls to the blood. The inner surface of the ileum is thrown into folds. These increase the surface area and the larger the surface area the faster the food is absorbed. On the folds are thousands of finger like projections called villi. These also increase the surface area and even have their own little projections called microvilli. There is a good blood supply to the ileum. Inside each villus is a blood capillary. The blood capillary absorbs amino acids and glucose. The blood supply is able to transport absorbed food to the rest of the body. Each villus also contains a lacteal. This absorbs fatty
acids and glycerol and is a branch of the lymphatic system Food
Fats Carbohydrates Proteins Vitamins and minerals Fibre
What you should be able to do.
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