The human body provides its own system of house cleaning. The liver, kidneys, intestines, skin, and lungs are constantly at work getting rid of waste materials. Some of the waste materials are taken in with food, but most of them are produced in the body itself. The more active the body, the more wastes there are, and the more cleaning must take place.
The work of the liver.
One of the most important organs for removing waste materials is the liver. This is a very large gland located on the right side of the body just below the lungs. It weighs about three and one-half pounds and is made up largely of tiny veins. Attached to the veins are countless little groups of cells known as globules. As the blood circulates it passes through the tiny veins carrying waste materials from the cells of the body. The globules on the veins work on the waste materials and change them into a substance known as urea, which is later removed from the blood by the kidneys. The liver also secretes a liquid known as bile, which is carried to the small intestine where it mixes with the food and helps to bring about digestion. In addition, the bile helps to remove waste materials from the body. It removes certain wastes from the blood, which it empties into the small intestine. The bile is stored in the gall bladder on the under side of the liver until it is needed for one of the foregoing purposes.
The work of the kidneys.
The urea, which is formed in the liver, is carried to the kidneys. These are two organs about the size of the fists shaped somewhat like butter beans. They lie in the back part of the body not far from the waistline. Each kidney is filled with many long, narrow tubes and tiny blood vessels. As the blood flows in from the liver, the waste materials pass through the walls of the tubes. Part of the water in the blood acts as a wash to carry the waste materials through. The water and waste materials together are known as urine. From the kidneys, the urine passes to the bladder. This is merely a sack holding about a pint which serves as storage for the urine until it leaves the body.
If the kidneys are to do their work properly, it is necessary that the body be supplied with plenty of water. If there is too little water, the kidneys become clogged and the urea is not removed from the blood. In order to supply his body with plenty of water to remove wastes, a person should drink from six to eight glasses daily.
The work of the large intestine.
When most of the digested food in the small intestine has been taken up by the blood, the part that remains passes on into the large intestine. A little absorption of food continues, but the chief purpose of the large intestine is to serve as a storage place for the waste materials from foods that have not been digested. The blood takes up more of some kinds of food than of others. Only a small part of cabbage, for example, is taken up by the blood as food, most of it passing on into the large intestine. This does not mean, however, that the unabsorbed part is useless to the body. On the contrary, it brings about greater activity and thus helps to move the waste materials along. Cabbage and other such foods which work in this way are known as roughage. Some of them should be eaten every day.
Usually if a person eats a well-balanced diet that includes plenty of roughage, he will have little trouble with constipation. It is important, however, that there be regular times for going to the toilet. Exercise, too, will help to prevent constipation. When waste materials are allowed to remain in the intestine too long, they begin to poison the body. If a person is troubled with constipation, he should see a doctor. Above everything else, he should not form the habit of using laxatives.
The work of the lymphatics.
The lymphatic system, as you have already learned, helps to carry food to the cells. It also does another very important kind of work. As it helps to feed the cells, it takes up waste materials. Often these materials include pus and germs from pimples or other infected parts. Some of the germs find their way into the blood, but most of them are destroyed by the lymphatic system itself.
Perhaps you are familiar with lymph nodes, or “kernels,” which may be felt on the sides of the neck and other parts of the body. These nodes are sieves in the lymphatic system for catching germs and particles of waste. They destroy many of the germs and break up the particles of waste. When they have to work very hard to protect the body, they sometimes become swollen and cause a great deal of pain.
The lymph is collected largely by the lacteals of the small intestine. It flows through the nodes and the network of lymphatic tubes into one large vessel which empties into a vein in the upper part of the trunk. Then it becomes the liquid part of the blood and goes everywhere in the body leaving food and taking up waste materials from the cells. The blood then carries the waste materials to parts of the body where they may be removed, such as the liver, kidneys, and skin.