Do Peoples Bodies Change Because of Where They Live?

In some cases, yes. The Indians of the Andes Mountains, on the west coast of South America, have developed bodies which are different from ours in order to survive where they live. At 17,000 feet above sea level, where these Indians live, we would find it very hard to breathe, but they do not.

The Indians' bodies have adapted in several ways. First, their lungs have grown bigger than ours, which means they can inhale and exhale more air with each breath. Then, too, they have about two quarts more blood in their systems than we do. They also have bigger red corpuscles to carry the oxygen. And their hearts are 20% bigger than ours.

The Indians also have shorter arms and legs to give the heart less distance to pump the blood, and smaller hands and feet, resulting in less of an area to be exposed to the cold.

How Are You Like Your Parents?

Every parent, human, animal, or plant, passes down certain characteristics to their children so that these offspring will resemble them, but not be exactly like them. This passing down of characteristics is called heredity.

When you began life as an egg produced by your mother and fertilized by your father, you came with a pre-packaged set of "directions" on how to grow and what to look like. These "directions" made you grow into a child rather than a dog or a plant, since each of those parents prepackage "directions" for their offspring as well.

All these "directions" are contained in 46 tiny body cells called chromosomes. Of these 46, 23 come from your father and 23 from your mother. These chromosomes carry tiny particles from each of your parents with all the characteristics you could inherit from them. These particles, called genes, are the detailed "directions" that decide not only what you will look like, your physical traits, but also what you will be able to learn your mental traits.

Among the physical traits you inherit from your parents are your general build, your skin color, your eye color and shape, your hair color and texture, straightness or curliness, plus the shape and size of your nose, ears, hands, and feet.

Among the mental traits you inherit are your ability to learn, plus talent in special fields such as art, music, mechanics, or science.

In addition, you inherit emotional traits, how you respond to certain situations or feelings, how easily you get upset or how calm you stay.

All these traits, however, are greatly influenced by your environment, the world you live in, what your parents and teachers teach you, and what you learn from your community.

There are, however, certain physcial traits that your parents may have now that you cannot inherit. For example, if your father has a scar that he got when he fell playing tennis, you would not inherit it. However, if he was born with a birthmark on his back, you might inherit that. If your mother had an operation to shorten or turn up her nose, you would inherit her old nose, not her new one. However, if she had freckles on that nose, you might inherit them.

The interesting things about your 23 pairs of chromosomes is that each pair of genes gives "directions" for only one particular trait. Your father may have given you a gene for blonde hair and your mother for brown hair. In many cases, one gene is more powerful than the other. This is called the dominant gene.

So if you have brown hair, that means that your mom's brown-haired gene was the dominant one, and your father's blonde-haired gene was the weaker, or recessive one. If your eyes are blue like your father's and not brown like your mother's, then you know that your father's gene for eye color was the dominant one and your mother's gene for brown eyes was recessive.

What Decides If You Will Be a Boy or a Girl?

There were two special chromosomes in you when you were just beginning life as a fertilized egg. These are called sex chromosomes. Scientist have named them the X chromosome and Y chromosome.

A woman's egg cell contains only an X chromosome, while a man's sperm cell Y contains either an X or a Y. If the woman's egg cell is fertilized by a sperm cell with an X chromosome, the fertilized egg will have two X's and the baby will be a girl. But if the sperm cell has a Y chromosome, creating both an X and a Y in the fertilized egg, then the egg will develop into a boy.

When Will You Stop Growing?

Girls reach their full height when they are about 18 years old, but boys keep growing taller for a few more years.

There are two periods in your life when you grow very rapidly. The first period began right after you were born and lasted until you were about six months old. The second period occurs when you reach your early teens. Girls grow faster than boys until they become teen-agers, then boys catch up and grow faster and stronger.

Your head stops growing earlier than the rest of you. When you were a newborn baby, you looked as if you were almost all head. By the time you were 10, your head was nearly full size.

The bones of your arms and legs were short when you were a baby. When you reached the age of 9, your bones started to grow rapidly and will keep growing until you reach your full height.

Besides growing taller, your body changes in other ways. When a boy is about 13 years old, his voice begins to get deeper and he may begin to grow a beard. About the age of 13, a girl's body begins to look and function like a woman's. Inside the bodies of both teen-age girls and boys, important changes are taking place, changes that make it possible for boys and girls, when they are older, to become fathers and mothers.

How Do You Grow?

When you eat, your food is broken down and sent to the cells of your body. These cells take in the food and grow bigger. Then each cell divides and becomes two cells exactly like itself. Each cell divides again, making four cells, and so on. This cell division goes on day and night. As the number of cells in your body becomes greater, you grow bigger and bigger.

When you are about 20 years old, a change takes place. Your plan for growing up is completed. From then on, your body stops growing taller, but the foods you eat keep your body in good running order, and help repair any worn-out parts. After you reach your full height, you may get fatter or thinner, but you won't get any taller.

Why Is Your Body Warm?

When you feel hot or cold, you are actually feeling the temperature of your blood. Since you are considered a warm-blooded animal (along with birds and other mammals), your body maintains an average temperature of 98.6° Fahrenheit (37.0° Celsius), no matter what the temperature is around you. Each species of warm-blooded animals has its own normal body temperature. Your normal body temperature is maintained by a part of your brain called the hypothalamus.

The hypothalamus, along with controlling hunger and thirst, is actually a "temperature center," which receives messages from nerves in your skin and deep in your body. It regulates the temperature of your blood by burning food to generate body heat when the air outside is cold, and cools your blood when the temperature outside is too hot.

Shivering and other physical activity also generate body heat in cold weather, while sweating and panting cools you off in hot weather. So whenever there is a change in the temperature of your blood, your body makes some adjustment to get it back to normal.

Cold-blooded animals (all those except mammals and birds), on the other hand, do not have this built-in brain control over their body temperature and must resort to other means. Reptiles, for example, crawl into the sun to warm up and seek the shade when they are hot. Some fish increase the action of their muscles to generate body heat.

Your body temperature does vary during the day. It is lowest in the morning, rises in the late afternoon, and falls again while you sleep!

When Did You First Start To Grow?

About nine months before you were born, you started to grow from just two cells. One cell, a sperm cell, came from your father. The other cell, an egg cell, came from your mother.

These two cells joined together inside your mother's body and formed a new cell called a fertilized egg. This cell was the very beginning of a whole human being, you.

When you were only a fertilized egg, you were about the size of the head of a pin!

How Does Blood Clot?

When you cut yourself, blood flows out of the wound. That blood contains, in addition to red blood cells and white blood cells, tiny structures called platelets. These platelets pile up around the wound, then combine with other substances in the blood plasma (liquid) and chemicals in the damaged tissue to form long sticky threads called fibrin.

Fibrin threads crisscross each other and form a kind of dam to trap the blood. This dam is a solid plug, or clot. A clot that forms over a wound on the surface of your skin is called a scab.

Because these platelets and clotting substances are always present in your blood, you may wonder why your blood does not clot while it is flowing through your body. That is because the clotting substances are inactive while your blood is circulating through the smooth walls of your blood vessels. If they were active, the blood would clot and block your circulation, a dangerous condition.

Each person's blood clots at different speeds. Those whose blood clots very slowly or not at all have a dangerous disease known as hemophilia. Doctors consider hemophilia a man's disease, because very few women have ever had it. But a mother who shows no signs of the disease can transmit it to her sons.

A person can lose as much as half of all the blood in his body and still live!

Does Everyone Have the Same Blood Type?

Everyone's blood isn't exactly the same, but this important fact was not known to scientists until 1900. Before then, blood transfusions were given from person to person without any thought to blood types. When it was discovered that in about half the cases, the patient got worse after a transfusion, and sometimes even died, scientists began to study why.

They learned that blood could be grouped, or typed, according to the presence or absence of a substance called antigens on the outside of the red blood cells. These antigens, if mixed with other "foreign" antigens, can cause the blood to clump, or stick together. This destroys the red blood cells, blocks the small blood vessels, and can cause serious illness or death.

But scientists also discovered that some blood types can be safely mixed without this harmful result. Therefore, when blood transfusions need to be given, hospitals today first perform a cross match, a mixing of some of the patient's blood with that of a donor, to be certain that the two types won't clump.

The four different blood types have been named type 0, A, B, and AB.

Type 0 blood has been found to mix safely with all the other types and has been called the "Universal Donor"!

How Does Your Blood Protect You?

Your blood has special cells in it that fight disease and infections. These cells, called white blood cells, are produced in your bone marrow, the, soft tissue that fills the inside of your bones. White blood cells work like an army to attack and kill harmful germs that get into your body.

When an infection develops on your skin, for example, the bone marrow produces more white blood cells than usual. These white cell "soldiers" move to the area where the germs are and actually chew them up and destroy them. They also eat away at the tissue around the germ, and soften and liquefy it. The white cells then break apart and, along with the destroyed germs and liquefied tissue, form the thick yellow-white substance called pus. The pus oozes out of the infection slowly and dries up as the wound heals.

Even though white blood cells are necessary to the body, too many of them can cause a disease called leukemia, a cancer of the blood!

Is Your Blood Really Red?

Blood looks as if it is solid red, but it really is not. If you look at blood under a microscope, you will see that it is made up of four different parts: plasma, red blood cells, white blood cells, and platelets.

The plasma, which is the actual fluid, is a yellowish-white liquid. It contains the red blood cells, the white blood cells, and platelets, along with proteins, minerals, digested food, and wastes.

However, there are more red blood cells in the blood than any of these other substances, and it is the hemoglobin, a red pigment, in the red blood cells that gives your blood its color.

Your blood has 18 billion (18,000,000,000) red blood cells in it!

How Much Blood Do You Have in Your Body?

The amount of blood in a person's body depends on how big he or she is, and surprisingly enough, on where that person lives.

For example, if you weigh about 80 pounds, you have about 2.5 quarts of blood in your body, while your 160-pound father has about five quarts, or twice as much. When you were an infant, perhaps about one month old, you had only about ten ounces of blood in your body.

If you live in high mountain areas where there is less oxygen in the air, you might have up to two more quarts of blood in your body. This additional blood is necessary to capture the extra oxygen your body needs to work and grow at greater altitudes.

How Does Blood Get Around Your Body?

Your heart is a kind of pump which sends blood to all parts of your body, since none of your cells can work or grow without it.

Blood has three main functions: it carries food and oxygen to permit your body's cells to work and grow; it carries wastes from these cells to organs which take them out of your body; and it helps fight germs that make you sick.

As your blood travels throughout your body doing these important jobs, it follows a definite route through tubes called blood vessels.

There are three main kinds of blood vessels: arteries, veins, and capillaries. When the blood is pumped out of your heart, it goes into your largest arteries, then moves into the smaller arteries, and into the capillaries. Capillaries are like bridges between your arteries and veins. They are such tiny blood vessels that you can't see them without a microscope. But these capillaries serve a very important purpose. They are like "traders," for it is through their thin walls that blood "trades," or exchanges food and oxygen for the waste materials that these body cells do not need.

Blood travels from the capillaries into tiny veins and then into larger and larger veins. Finally, the largest veins take the blood back to your heart. The round trip that blood makes is a continuous one which goes on and on while a person is alive. Each round trip from the heart, through the body, and back to the heart again takes less than one minute. And this round trip is made thousands of times each day.

If all the blood vessels in your body were straightened out and placed end to end, they would be 100,000 miles long, or long enough to go around the equator four times!

What Is a Nerve?

The billions of cells whose job it is to keep your body informed of conditions outside and inside it are called nerve cells, or neurons. Neurons transmit messages throughout the body by passing signals, or impulses, from one to the other.

Sensory neurons are nerve cells which carry impulses from the eyes, ears, nose, mouth, and skin to the brain and spinal chord. They allow us to see and hear, smell and taste, and tell us whether we are hot or cold, and let us feel pleasure or pain.

Motor neurons are nerve cells which carry these impulses from the brain to the muscles in the body, telling them to sit, stand, run, or talk.

Still other neurons work automatically, without signals from the brain. These neurons keep your heart beating, your blood flowing, your lungs breathing, and your stomach digesting food — all automatically, with no command from your brain.

Some impulses travel through your body at a speed of more than 300 feet per second, while others go as slowly as 1.5 feet per second!

What Are You Really Made Of?

All living things on earth, plants or animals, have one thing in common they are all made up of cells. Your entire body, your bones, your muscles, your skin, your blood, your teeth, your nerves, your hair, contains more than 10 million million (10,000,000,000,000) cells! Most of these cells are so tiny that you can see them only under a microscope. For example, your red blood cells are so tiny that 5,000,000 of them would fit inside a drop of blood the size of this letter a.

Different parts of your body are made up of different kinds of cells, and each kind does a special job that no other kind of cell can do. For example, muscle cells in your eyeballs move your eyes across this page you are reading, than nerve cells in your eyes send messages to your brain of what you have read. Red blood cells carry oxygen from your lungs to the rest of your body to help them grow as you are reading, while white blood cells are busy fighting off the bacteria that could make you too sick to go on reading.

Some cells are so tiny that even the most modern electron microscope, which magnifies 200,000 times and can enlarge an ant to a length of mile, cannot show the details of these tiny cells!