Our body is made up of thousands of different parts. All these parts work together to keep us alive and to help us move around. Some of the things we do require the strength of our MUSCLES. Other activities need the work of our BRAIN. All the parts of our body need to be kept strong and healthy. For example, we must have the right FOOD for our BONES and TEETH to grow strong and hard. We must sleep to rest our body and take exercise to keep fit.
Muscle cells, nerve cells, bone cells, cells in the intestine.
All living things are made up of tiny parts called cells. Our body consists of millions and millions of these cells. Each cell takes in food and oxygen from the BLOOD.
Cells are many different shapes and sizes and each of them has a different job to do, BONE cells need to be strong and firm so they are linked together in circles. The nerve cells are very small, but they have long nerve fibers. Messages travel along these fibers. Some fibers carry messages to the BRAIN, telling it what is going on. Others carry messages from the brain, telling each part of the body to do a particular job. MUSCLE cells are long and thin. They are arranged in groups for strength.
Our bones form a framework called a skeleton. This skeleton supports our whole body. Bones also help to protect the more delicate parts of our body. Ribs protect the HEART and lungs, and the skull protects the BRAIN.
Bone is a hard, whitish substance. Most bones are not solid but are slightly hollow. Inside is a fatty material, called marrow, where the BLOOD CELLS are made.
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.
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.
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 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.
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.
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.
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 goes 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 is passed into the large intestine or bowel. 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.
Breathing is the process of taking in and expelling air. We need air because it contains oxygen. Oxygen enables our body to release the energy contained in our FOOD and keep us moving. When you sit still, you breathe in and out about twenty times every minute. When you run about, you need more energy than when you sit still, and so you need more oxygen. You breathe more quickly when you are running - perhaps as much as fifty times every minute.
Air is drawn in through the nose or the mouth.
Next, it passes into the windpipe. The windpipe divides into two passages, called bronchi. One of these goes to each lung. Our lungs are like two large balloons in the chest. When we breathe in, the MUSCLES between our ribs lift the rib cage and the sheet of muscle at the bottom of the ribs, called the diaphragm, pushes downwards. When this happens there is more space inside the ribs and the lungs can swell up as air is taken in.
Inside the lung the bronchi divide again and again forming a network of small air passages inside the lungs. Each one of these air passages ends in a tiny air sac called an alveolus. BLOOD collects oxygen from the alveoli and carries it round the body to all CELLS. When the cells use the oxygen, they produce another gas called carbon dioxide. Blood carries this gas back to the lungs and we breathe it out.
We do not have to think about breathing because we do it automatically. The BRAIN sends signals to the diaphragm and rib cage muscles, telling them how often to relax and tighten and so make us breathe in and out.
Brain, spinal cord, cerebellum, nerves.
The nervous system gathers information about what is going on inside and outside our body using the SENSES and nerves. The BRAIN and spinal cord receive this information. They then send messages back which can make MUSCLES or GLANDS work. In this way we respond to situations around us. Sometimes we respond quickly and without thinking. If we touch something hot, we soon take our hand away. Often we choose what to do. When we cross a street we look, listen and thinks before we decide that it is safe to step forward.
The brain controls almost all the things that we do. Messages from all over the body pass to and from the brain along the spinal cord. Each part of the brain controls a different activity. Parts of the outer layer receive messages from the SENSES. Another area of the brain governs speech. The brain stores some information as memory. We learn from this memory and use its information to make decisions.
The five senses are: sight, taste, hearing, smell and touch. All the sense organs collect information in a different way. But they all send messages along nerves to the BRAIN, where they are interpreted and acted upon.
Light enters the eye through an opening at the center of the iris called the pupil. What we see is focused (made clearer) by the lens, and is recorded on the retina at the back of the eye. Within the retina are nerve CELLS that message to the brain about the colour and brightness of light entering the pupil.
Taste buds in the tongue give us a sense of taste. Different taste buds can recognize the four flavors: salt, sour, sweet and bitter.
The eardrum vibrates when sounds hit it. This in turn makes three small bones in the middle ear vibrate. The vibrations pass to the cochlea of the inner ear. Nerve cells in the cochlea inform the brain of the loudness and pitch of the sound waves entering the ear.
Many substances give off a scent or smell. The smell consists of millions of tiny particles which float in the air. We use our noses to detect them. When we smell a flower, for example, the particles are drawn up the nose to the smell cells in the upper part of the nasal cavity. The cells tell the brain what kinds of particles they are.
Nerves in our skin give us a sense of touch. We can feel whether objects are rough or smooth, wet or dry and we can respond to sharp pressure. Fingertips and lips are the most sensitive areas.