Page 19 - Curriculum Visions Dynamic Book

Kidneys
The kidneys have the task of filtering out waste products from the body. The kidneys keep most of the sodium
that is in the body, but up to five grams of sodium (a small teaspoonful) are excreted each day. Because sodium is so vital to the functions of the body, animals must make up this lost sodium in the food they eat. Fortunately, a normal diet provides this amount.
Sometimes kidneys fail, causing toxic wastes and fluids to build up in the blood. When this happens, patients are put on a blood-filtering, or dialysis, machine.
The first artificial kidney used a drum with a semipermeable membrane made from cellophane. The drum was bathed in a saline solution, while blood entered the drum.
The saline solution attracted out the wastes from the drum by osmosis, leaving the blood clean. Since then, major improvements to the process have been developed, but the principle of cleaning the blood remains the same.
 As this patient waits for treatment in a hospital, a saline drip is being used to regulate the blood.
digestive tract: the system of the body that forms the pathway for food and its waste products. It begins at the mouth, and includes the stomach and the intestines.
molecule: a group of two or more atoms held together by chemical bonds.
osmosis: a process where molecules of a liquid solvent move through a membrane (filter) from a region of low concentration to a region of high concentration of solute.
Blood
Kidneys remove waste products including excess salt.
Salts are extracted by the small and large intestines.
The effect of much or too little salt
Salt is vital to the working of the body. When we lose salt, such as through perspiration when we are hot, then the body’s method
of getting foods to the cells is reduced. As a result, we feel weak and may also feel sick. The same problem is caused when we are ill and, for example, we lose a lot of body fluid by diarrhoea.
As we lose salt, our body reacts by wanting to get more salt. This is why we sometimes crave salty things.
We can also become ill if we take in too
much salt. Salt controls the pressure in the bloodstream, and too much salt can lead
to high blood pressure and the risk of damaging the heart. Normally, we get rid of excess salt by sweating it off through the pores in the skin. This is the reason your skin sometimes tastes salty if you lick it. But if we take in far too much salt (say if we were to eat a tablespoon of salt), the body reacts to this by ejecting the salt through vomiting.
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