Main->Readings->5th Grade Readings->Control Systems ->Part 3
Vocabulary |
The nervous system has a big job controlling your body, but it does not have to work all by itself. There is another system in your body which controls how you act, think, grow, and develop. This system, the endocrine system, is made up of many glands, but unlike the nervous system the parts of the endocrine system are not really connected to each other. Hormones, like nerves, carry messages all over the body, but they must travel through the blood. Glands are organs or tissues that make and release chemicals, and they are all in different parts of the body. The chemicals released by the glands are called hormones.Your body makes and releases hundreds of these chemicals, each one with its own special job.
One gland is actually part of your brain, and is a sort of bridge between the nervous system and the endocrine system. This is the hypothalamus (hye-po-THAL-uh-mus). The hypothalamus releases many hormones, many of which actually control other glands, including the pituitary gland.
The pituitary (ph-TOO-uh-tair-ee) gland is also in the brain. It is sometimes called the "master gland" because it controls so many things, even though it is tiny. One of the hormones the pituitary releases is growth hormone. This hormone sends messages to cells which make them get bigger and more numerous, allowing human beings to grow from tiny infants to full-sized adults.
There are many other glands: the pineal, thyroid, parathyroid, thymus, adrenal, reproductive, and pancreas glands. Each makes its own hormones.
The thyroid (THYE-roid) gland, for instance, is found in the neck, just below and in front of the voice box (larynx). Thyroid hormone is important for controlling how fast the body releases the energy in the food you eat. If you have too much thyroid hormone, you are very active and you burn up your food quickly, and have to eat a great deal to keep from losing weight. You might think this is great, but it can be very uncomfortable to have too much thyroid hormone. On the other hand, people with too little thyroid hormone are very tired and sluggish. They gain weight easily, even when they don't eat very much.
The pancreas (PAN-kree-us) is another important gland, found under the stomach. The pancreas produces insulin (IHN-sue-lihn). The cells need the right amount of blood sugar to work properly, and insulin makes blood sugar move from the blood to the cells. With too little insulin, sugar collects in the blood and cells do not work properly. This condition is called diabetes (dye-uh-BEET-eez), and people who are diabetic may have to take insulin and be very careful about what they eat and when they eat.
The two adrenal (uh-DREE-nul) glands are on top of each kidney. One hormone the adrenal glands make is adrenaline (uh-DREN-uh-lihn), which is sometimes called the "fight-or-flight" hormone. When you are frightened, startled, or think you are in danger, adrenaline makes your eyes open wider, your heart beat faster, and your breathing speed up. It sends blood to your brain and muscles. This way, you are ready to act quickly. Quick action might mean dealing with the situation or it might mean running away from the situation, whichever the conscious mind decides is best. This is why it is called the "fight-or-flight" hormone.
There is one set of glands which are different for males and females. These are the reproductive glands: the ovaries in the female and the testes in the male. Ovaries make eggs and testes make sperm, but both of these glands also produce important hormones. One hormone that is important for females is estrogen (ES-troe-jen), although others are also important. A hormone that is important for males is testosterone (tes-TOSS-tuhr-ohn). These hormones trigger important changes as boys and girls mature. For instance, boys get lower voices, broader shoulders, more hair, and larger muscles as they mature.
Hormones are remarkable chemicals. We have talked about only a few, and there are hundreds of them in the human body. For instance,the adrenal glands, in addition to making adrenaline, also make about 30 different steroids. Aren't steroids bad for you? Not all steroids--there are many different kinds of steroids, many of them necessary to keep you going. But whenever someone fools around with the balance of hormones in the body by taking in other hormones from outside, there are always unexpected problems. Even diabetics must be careful when they take insulin, because of the problems it can cause. The body has to stay balanced.
In the next part, we will talk about the ways outside chemicals can interfere with the balance of your nervous system and your endocrine system.
Go on to Lesson 4: Matter Over Mind
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This page last updated May 28, 2003