The digestive system

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A few people eat so little that they suffer from anorexia. They worry so much about fat that their body mass drops dangerously low. They keep eating because there is a “voice” in their head that says they are fat
Most people that suffer from this are between the ages 15 and 25. They have health problems like:
• Pale, papery skin
• Reduced resistance to infection getting ill quickly
• Irregular periods
Vegetarian don’t eat meat. But you can’t just leave the meat on the side of you plate. They have to replace it by other forms of proteins, like cereals, seeds or nuts.
There are different kind of vegetarians. Some don’t eat meat but they do eat fish. Others no meat or fish but dairy products.
Vegans don’t eat animal products at all. No milk, no meat, no fish.

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You need small, regular amounts of vitamins and minerals. Vitamins and minerals are essential for good health. They must be present in our balanced diet. When we don’t have them we get ill.
Name Rich (food) sources Use in body Deficiency disease
Vit. A Carrots, milk, butter, liver Good eyesight, healthy skin Sore eyes, poor night vision, unhealthy skin
Vit. B1 Yeast, cereals, beans, egg yolk (ei geel)  Healthy nerves, growth Beri- beri (retarted growth) Not normal growth
Vit. C Citrus fruits Tissue repair, resistance to disease Scurvy (bleeding gum)
Vit. D Fish oil, milk, butter, made by body in sunlight Strong bones and teeth Rickets (soft bones)
Iron Liver, meat, cocoa Healthy red blood cells Anaemia (bloed tekort)
Calcium Milk, green vegetables Strong bones and teeth Rickets (soft bones)
Iodine Fish, iodised salt tablets Thyroid gland Goitre (enlarged thyroid)

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Your body consists of 2/3 out of water. You take in water when you eat and drink. Without food you could live for a few weeks. But you can only survive a few days without water.
Why do we need water?
• In our cells, chemical reactions take place in water
• Waste chemicals are passed out of our bodies in water
• Our blood transports substances dissolved in water
• Water in our sweat cools us down
Dietary fibre or roughage comes from plants. It is mainly cellulose from plant cell walls. Although it can’t be digested, it is an important part of your diet.
Fibre is important because:
• Fibre adds bulk to our food.
• Fibre absorbs poisonous wastes from digesting foods.
• It prevents constipation
• Many doctors believe that a high- fibre diet lowers the level of cholesterol in the blood. Fibre reduces the risk of heart disease and bowel cancer.

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When some foods are manufactured, chemicals are put in them. These chemicals are called food additives.
They are added because:
• Preservatives keep the food fresh
• Flavourings replace the flavour of the food that is often lost when it is processed.
• Colourings make the food look more attractive and appetising.
Some people avoid eating food additives because they think that they are harmful. Some may cause asthma and headaches. Others are blamed for over-activity in children. There is evidence that some additives destroy vitamins.

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Before your body can use the food you have eaten it must be broken up into very small molecules.
Large food molecules like proteins must be broken down into small amino acids. Proteins to amino acids
Large carbohydrate molecules like starch must be broken down into small sugar molecules. Carbohydrate to sugar
Large fat molecules must be broken down into small fatty acids. Fats to fatty acids

The breakdown of large food molecules into small food molecules is called digestion.
When the food has been digested, it is absorbed through the wall of the gut (digestive system) into the blood. But before they can go through they must be dissolved.
Large food molecules are insoluble: they will not dissolve.
Large food molecules can’t get through the gut wall.
Small food molecules are soluble: they will dissolve.
Small food molecules can get through the gut wall.

Enzymes are important chemicals. They help digestion by breaking down large food molecules into small food molecules.
The three main kind of enzymes in your gut:
• A protein molecule is made up of many different amino acids – protease breaks down protein molecules
• A starch molecule is made up of many glucose molecules – carbohydrase breaks down carbohydrate molecules
• A fat molecule is made up of fatty acids and glycerol molecules – lipase breaks down fat molecules

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Your gut (digestive system) is about 9 metres long. It starts at your mouth and ends at your anus. But your gut isn’t just a simple tube. There are many different parts.
Ingestion is the process of taking food and drinks into the body through the mouth.
The chewed food is mixed with saliva. Your salivary glands make saliva.
• Saliva contains a carbohydrase enzyme called amylase. This starts to digest starch to sugar.
• Mucus is a slimy substance in saliva. It helps the food slip down your throat.
Swallowing is a reflex- it happens without you noticing.

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The (o)esophagus (also known as gullet) passes the food down to your stomach.
The esophagus has circular muscles in its wall. These muscles contract and squeeze in behind the food to push it down.
In front of the food the muscles relax. This means it is pushed down
This way of moving food down your gut is called peristalsis.
Your stomach is a muscular bag that will hold up to 2 litres of food. When your food reaches your stomach it:
• The stomach makes digestive juices. These contain proteases which start the digestion of proteins to amino acids.
• The juices also contain hydrochloric acid (can burn a hole through the table, so sour is it). This is because stomach protease works best in an acid pH.
• Babies make the enzyme rennin. It makes milk solid so it stays in the stomach longer. The milk can then be digested.
• The muscular walls churn up the food making sure that it is mixed up well with the juices.
The stomach acid also kills germs.

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The (o)esophagus (also known as gullet) passes the food down to your stomach.
The esophagus has circular muscles in its wall. These muscles contract and squeeze in behind the food to push it down.
In front of the food the muscles relax. This means it is pushed down
This way of moving food down your gut is called peristalsis.
Your stomach is a muscular bag that will hold up to 2 litres of food. When your food reaches your stomach it:
• The stomach makes digestive juices. These contain proteases which start the digestion of proteins to amino acids.
• The juices also contain hydrochloric acid (can burn a hole through the table, so sour is it). This is because stomach protease works best in an acid pH.
• Babies make the enzyme rennin. It makes milk solid so it stays in the stomach longer. The milk can then be digested.
• The muscular walls churn up the food making sure that it is mixed up well with the juices.
The stomach acid also kills germs.

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Your small intestine itself is about 6 meters long. The liquid food is squeezed gently along it. 3 important liquids are added to the food:
• Pancreatic juice (made by the pancreas) contains carbohydrases, proteases and lipases. These enzymes carry on digesting the food.
• Bile enters the small intestine from the bile duct. Bile is made by the liver and stored in the gallbladder. It has 2 important functions:
1. Bile is alkaline and neutralises acid which was added to the food in the stomach. This gives the best pH for enzymes in the small intestine to work.
2. Bile emulsifies fats (breaks down large drops of fats into small drops). This increases the surface area of fats for lipase enzymes to act upon.
• Intestinal juice is made by glands in the wall of the small intestine. It also has carbohydrases, proteases and lipases in it. These enzymes complete the digestion of the food:
Starch  carbohydrases  sugar
Proteins  proteases  amino acids
Fats  lipases  fatty acids and glycerol.

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The small intestine has another important job apart from digestion. Digested food has to pass through the wall into the blood.
The small intestine is well designed for absorption. It has:
• A thin lining
• A good blood supply
• A very large surface area
The surface area of the small intestine is about 9 m2. How does this large surface area fit into such a small space?
• It is very long (6 meters!!!)
• It has a folded inner lining
• It has millions of tiny, finger- like processes called villi
All this means that the digested food can pass easily through into the blood vessels.
By the time your food comes into the large intestine there’s not much useful food left. It’s mainly fibre, dead cells, bacteria and water. As it passes along some of the water is absorbed into the blood.
The solid waste (faeces) poop are stored in the rectum. The passing out of indigestible food through the anus, in the form of faeces, is called egestion.
Normally it takes 24-48 hours for food to pass through the whole body.