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The digestive system

Let's follow the route of a piece of toast, to take a look at the digestive tract. After putting the toast into our mouth we chew it with our teeth. Not only is the toast ground into small pieces, but it is also mixed with saliva. Saliva contains enzymes. These enzymes break down molecules into smaller particles. A piece of toast is made of wheat and this contains starch. Starch is made up of long chains of carbohydrates. These chains are too small for the teeth to grind but the enzymes break these into smaller pieces. In other words, digestion starts in the mouth! So it is very important to chew your food well and not to rush it.


After swallowing, the toast will go past the back of the throat, down the gullet to the stomach. The stomach contains very acid fluid and enzymes to break down the chain of molecules into even smaller pieces. The stomach's contents are so acid that, if you could put your finger in there, it would be broken down as well! Because of the acidity, most of the bacteria will be killed. The stomach can survive this acidity because it has a special lining. You could say that the lining is greasy and regenerates itself constantly. You could compare it to a slate roof which is being re-slated constantly from the inside. The slates on the outside are constantly sliding off the roof. Likewise, the stomach's outer cells are constantly being shed; in other words, the lining of the stomach is constantly being renewed.

After passing through the stomach, the food content reaches the small intestine. As we know, the stomach content is very acidic, so how is it that the small intestine survives this acidity? This is because the acidity is neutralised by alkaline fluid. The pancreas secretes this alkaline fluid, and adds further enzymes to break down the food particles into even smaller particles. We all end up with the tiniest of particles floating around in the small intestine. You can see that digestion takes place in the upper part of the digestive tract.

Now the question is, how do these food elements that are floating around in the small intestine come to be used? All these tiny little particles are taken up through the wall of the intestine into the bloodstream. These vessels fuse together like a vast oriental fan, into one huge blood vessel, which goes into the liver. This is called the portal vein. (Fat particles take a different route. After passing through the lining of the small intestine, they will find their way into the lymphatic system, which then leads through the superior vena cava to the heart, but they will also be transformed in the liver).

Why do all these blood vessels lead to the liver? Well, to answer that question, it is important to look at the function of the liver. The liver has three main functions, (i) to detoxify poisons, (ii ) to store nutrients like sugar, iron, Vitamin B12, and (iii) to produce bodily substances. It is an incredible thought that the process of becoming physically human happens in the liver. As we have seen, we eat plant material such as wheat (toast) but it is the liver which makes our human substance out of these little plant building blocks which have been absorbed in the small intestine.

Here we can see again that the building-up or anabolic process takes place in a carbon dioxide (CO2)-rich environment. The blood vessels that bring these building blocks to the liver are (CO2-rich) veins.

After useful food stuffs have been taken out of the fluid in the small intestine, what happens to the remaining fluid? If it passed through from the small intestine to the large intestine and straight on, you'd end up with diarrhea. As you know, the waste product of digestion is rather more solid than diarrhea. Why? Because the function of the large intestine is to absorb all the fluid back into our body instead of giving it to the toilet. The large intestine (or colon) actually needs to extract an amazing amount of fluid, about 14 pints (7 litres). Even if you don't drink anything, your digestive tract creates a waterfall of fluid, which needs to be recycled by the colon. Every day we produce up to one litre of saliva. If you have ever had a sore throat you know how often you need to swallow during the day. The stomach produces about 4 pints (2 litres) of fluid, the small intestine 5 pints (2.5 litres) of fluid, the gall bladder one pint (0.5 litre), and the pancreas 2 pints (1 litre) of fluid. Now you can imagine why a tropical disease like cholera can be very dangerous. This illness affects the colon, and prevents it from absorbing water properly. So, a person with cholera could have diarrhea causing fluid loss of up to 14 pints (7 litres) a day. This is too much for the body to lose, as we have only 8 pints (5 litres) of blood. The treatment for people with cholera is basically to give them just as much fluid as they lose per day (together with a bit of salt and sugar). On the other hand, you can now perhaps understand why when people become constipated, the faeces become hard; because the colon keeps on extracting fluid, it impacts the stool.

Diarrhea

A viral infection of the lining of the large intestine is the most common cause of diarrhea. The virus will affect the lining of the colon and cause it to function less efficiently. More water will remain in the colon, and this causes diarrhea.

The best way to treat common gastroenteritis like this is with a special diet; avoid diary produce: no milk, cheese or eggs. Fatty foods such as these can set the diarrhea off again. It is best to reduce your protein intake (meat, beans, etc.) Do not take any stimulating drinks like tea or coffee. It is best to stick to carbohydrates such as white bread with jam, white rice or pasta and (diluted) fruit juice.

Babies, though, should be allowed to continue to breast feed, and you should not exclude dairy produce from a toddler's diet for more than few days, because this could maintain the diarrhea. Overall, fluid intake is very important. Particularly with babies and young children, it is wise to consult your doctor.





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