Muscles

Biceps contracted, triceps relaxed, biceps, tendon, triceps

Muscles are made of strong fleshy fibers. At each end they are firmly attached to a BONE by a tendon. By pulling on the bones, muscles enable us to move. Without muscles, it would be impossible for us to make movements at all. The HEART is made up of a special kind of muscle. As this muscle contract, the heart beats. Heart muscle works continuously and tirelessly throughout our lives. EATING involves muscular movements of our digestive system.

Blood

Heart, artery, vein, corpuscle.

Blood is a red liquid which travels throughout the body. It is carried in a network of tubes. The largest of these tubes are called arteries and veins. The smallest branches are called capillaries. Blood takes with it the food and oxygen which keep the body alive and working properly.

Blood is made up of many red CELLS and a smaller number of white cells. Red blood cells are like tiny discs. They carry oxygen. White blood cells are larger. Their job is to fight disease. They surround and destroy harmful particles like BACTERIA which sometimes get into the blood. Blood cells are commonly known as corpuscles.

If you cut your finger, blood will start to flow out. But it soon thickens or clots to prevent too much escaping. A healthy child has about four liters of blood, a healthy grow-up person has about six liters.

Heart

Left auricle, left ventricle, right auricle, right ventricle

The heart is a kind of pump which drives BLOOD through the body. An adult’s heart beats about 70 to 80 times a minute when he is standing still.

When you are running about and playing hard, the body needs more food and oxygen. Then the heart beats faster, pumping the blood, with its food and oxygen, quickly through the body.

Blood flows along the veins into the right side of the heart. From there it is pumped to the lungs where it takes in oxygen from the air. It comes back from the lungs into the left side of the heart. From there it is pumped into all parts of the body through the arteries. Valves in the heart prevent the blood from flowing backwards.

Teeth

Flat incisor, pointed canine, grinding molar, dentine, enamel, nerves, blood vessels, jawbone, root.

Teeth are for chewing FOOD. At the age of about six months, the first set of 20 teeth begins to grow through the gums. These first, or ‘milk’, teeth are soon lost. They are replaced by 32 permanent teeth. By the time you are about 14 years old you should have nearly all your permanent teeth.

Each tooth is held into the jawbone by a root that is hidden by your gums. The hard white part that you can see in the mouth is called the crown. The crown is covered by a hard layer of enamel. Under the enamel is a thick layer of strong material called dentine. The center of the tooth is made up of softer pulp that contains nerves and BLOOD vessels.

Skin

Pore, germ, sweat.

The whole of our body is covered by skin. It protects us against injury and germs and also gives the body information about changes in temperature.

The skin is divided into two layers. The outer layer is dead. CELLS flake off from this all the time. Underneath this protective layer there are thousands of sensitive cells. All over the skin are tiny openings called pores. Sweat escapes through these pores to cold the body.

Hair

Dead layer, pore, sweat gland, living layer, hair follicle, hair, nerves, layer of fat

Hair grows on nearly every part of the human body. It is most noticeable, however, on the head.

The hair on our head usually grows about 15 centimeters a year.

Each hair grows from a root in its own follicle, or opening, in the SKIN. Every follicle has a GLAND which supplies oils to the hair and to the skin. The follicle also has a MUSCLE attached to it which makes the hair stand on end when we shiver. Normally, each hair lies flat against the skin.

Eating

Mouth, esophagus, stomach, large intestine, appendix, small intestine, anus.

The FOOD we eat helps to give us energy. It has a long journey to make before all its goodness has been taken into our body.

When we put food into our mouth, it is first chewed into tiny pieces by our TEETH. These pieces of food are then mixed with a juice called saliva. Saliva is made in GLANDS in the mouth. It is produced whenever food is put into the mouth. Saliva contains special chemicals, called enzymes, which begin to digest the food.

The food is then swallowed and down the food pipe, or esophagus, into the stomach. Here it is mixed with digestive juices and turned over and over until a thick liquid is formed. The food takes up to six hours to be digested in the stomach, depending on the size of the meal.

A little at a time, this liquid leaves the stomach and passes into the small intestine. The small intestine is a coiled tube about seven meters long. In the small intestine, more enzymes are added to the liquid to complete the digestion process. All the goodness from the food then passes through the walls of the intestine and into the BLOOD. The digested food is carried in the blood along the arteries and veins to the Cells of the body.

Any undigested food passed into the large intestine or bower. This tube is wider than the small intestine, but not as long. In the bowel the water is taken out of the waste food. In its more solid form the food passes out of the body through the opening called the anus. The complete digestive process takes about 24 hours.

The appendix, located close to where the large and small intestines meet, serves no purpose in humans. When it is infected, it becomes inflamed and fills with pus. This condition is called appendicitis.

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