Skeleton:
The section uses the terminology as outlined in the Human Body. Jenny Clarke; illustrations by Kate Crowle. Macmillan Australia Science WallCharts, c1985, 1988.
The complete set of bones in the body is called the skeleton. The skeleton is the framework which supports and gives shape to the body. It also protects the organs inside.Without the skeleton we would not be able to move or even to stand.
There are more than 200 bones in the body. Most people have 206 bones making up the skeleton but some people have an extra rib or an extra bone in the backbone. The biggest and the longest bone in the body is the thigh bone or femur and the smallest bones are the tiny bones of the middle ear.
Bones:
Bones are harder because they contain minerals such calcium. They are not
solid. Most bones, while being hard on the outside, are hollow or spongy
on the inside. They contain blood vessels and nerves. Bones are covered
in a tough skin called the periosteum. Therefore they are rigid enough to
support us but flexible enough not to snap easily.
The skull (cranium) protects the brain, the eyes, and supports the face. The skull is made up of nine major bones, and many smaller bones. The shoulder is made up of two bones, the collar bone (clavicle) and shoulder bone (scapula).
The ribs are made up of twelve pairs of curved bones which protect the heart and the lungs. They are joined to the breast bone (sternum) and connected at the back to the backbone.
The spine, which is also called the backbone, is our central and most important group of bones. It is made up of twenty-six bones called the vertebrae and is attached to the skull, the collar and the shoulder bones, and the ribs and hip bones. It protects the spinal cord and enables movement. Vertebrae at the lower end of the spine form a bone called the coccyx.
Joints:
Where the bones of the skeleton meet they form joints. Whenever you move
you use one or more of your joints. For instance, when you move your leg
you use your hip,knee and perhaps ankle joint. Joints,then, enable you to
make all kinds of movements, such as walking, turning and bending.
There are four main types of joints connecting the bone of the skeleton. Three of these types of joints are movable, one is fixed. The bones of the skull must be firm to protect the brain and therefore are fixed for life.
In three movable types of joints, the ends of the connecting bones are covered with a tough, flexible membrane cane called cartilage. This membrane or cartilage prevents the two bones rubbing directly against each other. They are also 'oiled' by a special fluid. This fluid enables the bones to move smoothly against each other. The bones are held together by ligaments.These three joints are called the sliding joints, ball and socket joints and hinge joints.
Muscles:
When you move any part of your body you use muscles. They are connected to
your bones by fibrous tissue called tendons. Muscles help to control the
moving parts of your body. For instance, when you want to eat, the
muscles in your cheeks work your jaw so that you can open your mouth. When
you walk, you use the muscles in your legs.
Just under half the body's weight is made up of muscles. There are over 650 of them in the body. Some muscles are large and help us to move our legs and arms, and to lift heavy weights. There are also tiny muscles which help us to smile, blink, twitch or to frown. Muscles help you to digest your food and keep your blood moving. Every kind of movement involves at least one muscle.
Muscles work by pulling. They usually work in pairs, one pulling one way (contracting) and the other relaxing. Muscles never totally relax even when we are still or lying down. They are continually keeping the bones in position. Apart from the heart, the main different groups of muscles are voluntary and involuntary.
Heart:
Your heart is the hardest working muscle in your body. It began working
before your born and beats 60-80 times per minute. In the normal life
time the heart will beat about 2500 million times, pumping about 200
million litres of blood around your body in that time. The heart is about
the size of a clenched fist and found between the lungs, a little to the
left of the centre of your chest.
The heart is a pump made up of four parts. There are two chambers on each side of the heart. One chamber on each side receives the blood. These chambers are called the right and the left auricles. The other two chambers pump the blood to all parts of the body and are called ventricles.
Contractions of the heart muscle cause the valves between the chambers to open and close to let the blood in and out. This happens continually and is what we call our heartbeat.
Heart Muscle:
The heart or cardiac muscle is a very special type of muscle. It is
cross-striped or striated, and it is involuntary. You have no control
over its movements. It continues to work while you are asleep.
When you become hot, the muscles in the walls of blood vessels near the
surface of the skin automatically relax, allowing more blood through.
This helps to cool you down. When you are cold the muscles in blood
vessels near the surface of the skin contract, reducing the amount of
blood to that area.
Blood:
There are nearly 100,000 kilometres of blood vessels in an adult human
body. In the veins, the blood travels slowly. The movement of blood
through the veins is helped along by contractions of the leg and arm
muscles. Veins are shown in blue. Arteries are in red.
The system which transports blood around your body is called the circulation System. Blood is important to the body because it carries oxygen from your lungs to all your limbs and organs, and food from your digestive system to every part of your body. Blood is continually moving around your body in a network of thin tubes called blood vessels. The heart is the pump which keeps the blood moving round and round through your body.
The vessels that carry the blood containing oxygen from the heart to the parts of the body are called arteries. When the arteries reach the muscles and other tissues they split into thousands of small blood vessels called capillaries. These capillaries are very tiny but most of the blood vessels in your body are capillaries. When the blood reaches the capillaries it passes out the oxygen and 'fuel' and picks up any waste and returns to the lungs via the heart to pick up more oxygen. The blood vessels that carry the blood on the return journey are called veins. The bigger you are the more blood your body contains. A baby has about and a half litres of blood, a child about three litres and an adult about five litres.
Blood looks a thick red fluid, but just over half its volume is a straw-coloured liquid called Plasma. Floating in the plasma are red cells (corpuscles) and platelets. The red cells give the blood its colour and carry the oxygen from the lungs and take it to all parts of the body. These cells work very hard and have to be replaced at a rate of over 100 million per minute. The white blood cells are less numerous, but they help to defend the body against disease. The platelets, which are very small, help the blood to clot when you are cut or wounded, and so help the bleeding to stop.
Lungs:
We cannot live for longer than several minutes without oxygen. Breathing
is something you do automatically, even when you are asleep. You have two
lungs which are spongy bags of tissue protected by your ribs. When you
breath, you take in air through your nose and mouth, down through your
windpipe, and into your lungs.
The windpipe(trachea) forks into two main tubes called bronchi, one to each lung. These tubes divide again and again into a fine network of tiny tubes (called bronchioles) throughout the lungs. Each tube ends in a tiny thin-walled sac which is surrounded by many small blood vessels or capillaries.
Each lung contains thousands of these little sacs. These sacs put oxygen back into the blood. Then the heart pumps oxygenated blood back around the body.
Eyes:
Our eyes weigh only seven grams each and are two centimetres in diameter.
They contain over 100 million special cells which are sensitive to light
and with the help of the brain allow us to see the world. The main parts
of the eye are the cornea, pupil, iris and retina. The eyes are well
protected by the eye socket, eye lids and lashes, and by the eye brows.
The front of each eye is a transparent layer called the cornea. The cornea focuses light entering the eye with the help of the lens and fluid behind it. The cornea is kept moist by tear fluid which is spread over it by blinking.
The dark area in the centre of your eye is hole behind the cornea called the pupil. It controls the amount of light entering the eye, like a camera lens. It opens wide in dim light and becomes smaller in bright light. The iris is the coloured ring of muscle around the pupil. It contracts to open the pupil, and helps to protect the eye.
What you see is focused on the retina, the membrane at the back of the eye. Here the picture is upside down, but your brain makes you see it in the right way up. The retina has many light-sensitive cells called rods and cones. The rods react to light even in semi-darkness. The cones help you to see colours. The cells in the retina are attached to nerves that go the brain which works out what you have seen.
Ears:
Our ears are important for two reasons. They are the organs of hearing,
and they are also the main organs of balance. The ear is divided into
three main parts-outer, middle and inner.
The outer ear picks up sounds which travel along a short tube to the ear drum. This is a tight membrane which vibrates when sounds hit it. These vibrations then cause the tiny bones of the middle ear to move and pass the sound along a membrane to the inner ear.
The inner ear is the series of tubes which are filled with fluid. The final tube is coiled and called the cochlea. The sound makes its way through the fluid in these tubes to the cochlea where the vibration causes a message to be passed along the nerve from the cochlea to the brain.
It is this liquid-filled tubes in the inner ear which help you to keep your balance. When you move your head in one direction the fluid moves in the opposite direction and bends the tiny hairs inside the tubes. The hairs are connected to nerves which pass messages to your brain. Your brain then knows the position of your head. Your inner ear works in much the same way as a spirit level to help you keep your balance.
Brain:
The centre of your nervous system is your brain. The brain is more
complicated than any man-made computer and contains about 14000 million
cells. It is the control centre for the body. The brain controls all our
other organs as well as our thoughts and feelings.
Our nerves link the brain to all other parts of the body, like a network of telephone lines. When you see or touch or smell something, messages travel along nerves to your brain. Your brain then tells you what you have seen or smelled or touched. Other nerves control muscles so that you can sit, stand, walk, run, skip and jump.
The brain has many parts. The medulla connects the spinal cord to the brain. It controls breathing and heartbeat. Above the medulla are the midbrain and pons that control body movements which we are often unaware of, for example, the movements of the eyes.
The largest part of the brain is the cerebrum. This is large, dome-shaped and wrinkled, and takes up most of the skull or cranium. It is divided into two halves or hemispheres. The left hemisphere of the brain mainly controls the right-hand side of the body and the right hemisphere of the brain controls the left-hand side of the body. These halves are then further divided into lobes which all have special jobs, such as controlling body movements, receiving sensations, memory and many other things. Underneath the back of the cerebrum is the cerebellum or "little brain". The cerebellum organizes balance, posture and co-ordination. Each part of the brain has its own job.
Male Reproductive System:
Every living thing in the world is capable of reproducing its own kind.
The reproductive system in humans is different in men and women and the
two must join to create a baby.
The male reproductive system consists of the penis, tests and vas deferens. A man has glands (called testes) which make millions of cells called sperm. They then pass along a tube called the vas deferens to the penis. A woman has ovaries which make eggs. When a sperm and egg (ovum) come together, this makes the fertilized egg which can then develop into a baby.
When a man and woman want to create a baby, the man's penis becomes stiff and is placed inside the woman's vagina. The sperm cells are then released (ejaculated) into the vagina to join with the woman's egg. About four hundred million sperm are released at each ejaculation, but only one fertilizes the egg.
Female Reproductive System:
The female reproductive system consists of ovaries, fallopian tubes, the
womb (uterus), cervix and vagina. Every month(about 28 days) a cyclical change takes place inside the womb. Each month, a woman produces one egg (perhaps more) which then passes
down the fallopian tube to the womb. The egg in the Fallopian tube can be
fertilized by the sperm. If this does not happen the egg dies and
bleeding occurs. About two weeks later a new egg is produced and the
cycle begins again. This is called the menstrual cycle.
When the egg and the sperm join together, the fertilized egg makes its home in the womb, which has been specially prepared. The womb provides food and oxygen from the mother's blood to the growing baby (embryo). During the nine months spent in the mother's womb the cells of the fertilized egg will divide many times to form millions of different cells. As the embryo grows to take on human shape it is called a fetus. From the time of fertilization to a birth of a fully grown fetus takes about 266 days.
Respiratory System:
The respiratory system contains all the parts of the body involved in
breathing. The lungs are the most important parts of our breathing system
but the nose, mouth, windpipe, ribs and diaphragm are also important.
The two passages through which air enters the body are the nose and the mouth. You should breath through your nose because the nasal channel to the lungs strains harmful dust particles and warms the air. Most harmful particles are trapped by tiny hairs in the nose. When you breathe through your mouth there is no filter and dust particles then have to be trapped by the sticky mucus in the windpipe, and will leave the body when you cough.
When the chest expands, air is drawn into the lungs. This happens when the diaphragm, the muscle underneath the lungs, is pushed down and flattened, and the ribs move up and out. When the rib muscles relax and the diaphragm is raised, the lungs are compressed and stale air forced out. This happens about twelve times every minute. Some air stays in the lungs all the time, otherwise they will collapse.
When you breath in, you take in air which is mostly nitrogen, some oxygen, and very little carbon dioxide. Inside the lungs, an air change takes place and you breath out more carbon dioxide and water vapour, which are produced by the body as it uses up some of the oxygen you have inhaled.
Senses (Touch, Taste and Smell):
The body has five senses-sight, hearing, touch, taste and smell
through which we learn about our world.
Under the skin the body ha many type of nerve endings.Some parts of the body have more nerve endings than oters. For example, your finger tips are very sensetive to touch because they have many nerve endings. The nerve endings under your skin are sensetive to five different sensations. They are the feelings of pressure, pain, heat, cold, and touch. This last feeling is the true sense of touch. When you touch something lightly you can feel its shape. Blind people use this sense when they read Braille.
The two senses of taste and smell work closely together and detect chemical substances, such as those creating flavour in food and smoke from a fire. There are four basic different tastes- sour, sweet, salty and bitter. Different parts of the tongue have taste buds to detect the different tastes. Taste and smell work together when you eat because you not only taste the flavour with your tongue, but also smell the flavour of food with your nose. For example, when you have a cold and your nose is blocked it is more dificult to tell the diference between foods.
Taste is detected by nerve endings on the tongue. Smell is detected by nerve endings in your nostrills. These nerve endings pass messages to the brain, eg. Sneezing.
Skin:
Skin is a waterproof covering for your body. It does many important
jobs. It protects the organs from injury and germs. It also helps to keep the body at the same temperature. When you get hot you perspire through your skin, the water evaporates and makes you cooler. Your skin has two layers. The thin top layer is is the epidermis which is mainly dead cells. These peel off. In a life time we shed our outer skin many times bit by bit. The thicker second layer of skin is called the
dermis. This layer contains blood vessels, nerves, sweat glands and
connective tissue. Ridges on the skin give you your own fingerprints which make you unique.
A special substance called melanin gives skin its colour. How dark your skin is depends on how much pigmentation your skin contains. People from different races have different coloured skin because of more or less pigment in the skin People with freckles have spots of pigment in their skin.
Hair:
Hair is a shaft coming out of hair follicle in the dermis, attached
to an oil gland and a tiny muscle pushes the oil out of the gland and a tiny muscle. This muscle pushes the oil out of the gland, up the hair and also contracts or tightens to make the hair stand up when you get goose bumps. Hair growth starts in the special cells ofg the follicle. When hair comes through the epidermis it is made up of dead cells, but the root in the dermis is living.
On your body you have about a quarter million hairs whic are replaced all the time. The hair on your head grows about 15 centimetres a year and is replaced every two or three years.
Digestive System:
Most people eat three meals a day ta regular times. The food you eat
passes through a system called the digestive system, which changes and breaks the food down to give us heat and the energy for all the of our body parts. This is a very slow system and it takes up to a day for the food to finifh its journey. The digestive system consists of the mouth, oesophagus, stomach, intestine and rectum.
When you put food in your mouth it is chopped, torn and ground by your teeth. An adult has 32 teeth of three different types to break down all sorts of food. The incisors are for chopping, the for tearing and the molars for grinding. The teeth chew up food. The salivary glands mix it with saliva. The tongue helps to mix the food with the saliva. The oesophagus is a short tube through which the food passes from the mouth to the stomach. The muscles in the wall of the tube contract to push the food along.
The intestine is about 9 metres in length. It has two main sections- the small and large intestine. Food passes into the small intestine in a semi-liquid form. It is mixed with fluids produced by the liver, pancreas, and cells in the intestine lining. The muscles in the wall of the intestine contract to continue moving the food through its length. The food is almost completely digested in the small intestine, which is covered with hundreds of tiny blood vessels. These take the digested food back into the body to give us nourishment and energy. Only food that cannot be digested is taken into the large intestine. Water is removed from the waste which passes out of the body through the rectum.
Your body needs food. It will tell you when you feel hungry. Different vitamins and minerals, as well as proteins, starches and fats. Foods like fish, meat, cheese, eggs and milk, contain lots of protein. They keep you strong and help you to grow. Other foods, such as bread, cereals and pastas, contain starch to give you energy. Many foods contain fats. Fat keeps you warm but you should not eat too much of it. It is a good idea to eat a mixture of the different kinds of food.
Waste System:
Our bodies burn food to give us energy, just as burning coal or wood
leaves waste gases and ash behind, so also our bodies produce harmful waste materials. These harmful products must be removed or our bodies wil not work well.
The removal of waste from the body is called excretion. The main organs which deal with this are called the kidneys. The lungs, liver and sweat glands of the skin also help to remove waste. We lose an average of 3 litres of water a day through our skin, breath and urine. The lungs expel carbon dioxide through the nose and mouth and the skin, through sweat glands, also sweats out salt. The kidney removes most of the waste. Solid wastes leave the body through the anus.
We usually have two kidneys. Both are connected to the bladder by long tubes called the ureters. The kidneys filter the blood and help to regulate salt and water in the blood. The blood is brought to the kidneys by the renal artery which then branches out into more than a million capillaries. When the blood has been purified it goes back to the body through the renal vein.
Fluid passes out of the blood and into the tubules ( which are in the kidneys ) every day. Here harmful substances are taken out of the fluid. The clean fluif then goes back into the blood. Therefore, valuable salts and water are kept in the body. The remaining liquid passes down the ureters into the bladder and out of the body as urine which is yellowish liquid.
If our kidneys do not work properly, our blood and tissues are poisoned by waste materials. One way of correcting this is for people to use a kideny machine. Here the blood is taken out of the body and cleansed by the machine before going back into the body. The machine does the work of the kidneys.
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Last updated February 19, 2001