My Science School

MEDICINE

          Occasionally the body is ill or suffers injury. From ancient times people have used many different methods - not always successfully - to help the sick and injured. Modern medicine is based on scientific tests and treatments rather than superstition or magic.

          Two main types of treatment are medical and surgical. Medical help involves chemicals or drugs. These may be obtained from natural substances such as plants, animals or microbes, or made in the laboratory (for example, chemotherapy, used to fight cancer). Surgery involves physical treatment, for example, cutting open the body during an operation, to remove a diseased part or mend a broken bone.

CLEAN CONDITIONS

          Before the invention of the microscope, no one could see germs. These are microscopic life-forms such as bacteria and viruses that invade the body and cause the illnesses known as infections. Since people did not know about germs, they did not understand the importance of keeping wounds clean. Surgeons never bothered to wash their hands or their instruments. Many more people died after operations than got better.

 

 

 

DOCTORS AND HOSPITALS

          A doctor is qualified to examine and treat people using drugs and surgery. A person who is ill usually goes to the family doctor or general practitioner (GP). The GP has a wide knowledge of medicine and can diagnose (identify) and treat most illnesses.

          If the cause of the problem is not clear, the person may be sent, or referred, to a hospital doctor or consultant. The consultant is an expert in a certain type of medicine. For example, a neurologist deals with problems of the brain and nerves and a cardiologist with diseases of the heart.

 

 

EMERGENCY MEDICINE

          Some of the greatest advances in recent years have been in emergency medicine. When a person is badly injured in a road accident or suffers a heart attack, every second may count. The ambulance crews are specially trained and equipped to give life-saving first aid and to care for the victim or patient on the way to hospital.

          At hospital the patient is taken to A&E (the Accident & Emergency department) where specialist doctors quickly decide on treatment. If an emergency operation is needed, the surgeon and team go to the operating room or theatre and begin straight away. After surgery, the patient is looked after in IC (the Intensive Care unit). Machines and monitors check the patient’s heartbeat, breathing, blood pressure and other body processes. If all goes well, the patient begins to recover and can leave IC for the general ward. Nurses carry out daily care and check on progress until the patient is well enough to go home.

Picture Credit : Google

A BABY GROWS

          It takes nine months for the fertilized egg to grow and develop in the mother’s womb, then become a baby ready to be born. This time is known as pregnancy. For the first eight weeks the developing baby is called an embryo. During this period, all of the main body parts and organs, such as the brain, heart, eyes, ears, and even the fingers and toes, form. At the end of eight weeks, the embryo is only about the size of a thumb-tip. But the main phase of development is complete and the baby looks like a miniature human being.

          For the next seven months the main change is in size. The baby grows at a faster rate than it will ever grow in the rest of its life. Finishing touches are added to the body, such as fingernails, toenails and eyelashes. During this growth phase the baby is known as a foetus.

 

EARLY DEVELOPMENT

          The part of the baby that develops fastest is the head, followed by the main body and then the limbs. In the early stages, the brain and spinal cord are by far the largest part of the body. During the fourth week, the main body begins to develop. The heart pumps blood through a simple system of tubes and the lungs begin to grow.

          Towards the end of the fourth week, the lower body organs, such as the intestine, liver and pancreas, form. The arms and then the legs also start to develop. At first they are tiny bumps on the body called limb buds, but they soon lengthen and the fingers and toes take shape.

          During the fifth week, the ears, eyes and nose take on more recognizable shapes. Main nerves begin to grow out from the brain and spinal cord. The kidneys and stomach also develop.

 

 

 

 

LIFE IN THE WOMB

          Inside the womb, the baby floats in a pool of amniotic fluid. The fluid cushions and protects it from bumps and jolts. The baby cannot breathe or eat in its watery surroundings. So it receives oxygen and nutrients from the mother through the placenta (also called the afterbirth). The baby can hear sounds such as its mother’s heartbeat. Loud noises from outside also pass into the womb and may startle the baby and make it jump. At first the baby has room to move and even turn somersaults. But as it grows larger it becomes more cramped, even though the womb stretches.

Picture Credit : Google

          The key feature of all living things is that they can make more of their kind. This is called reproduction. The human body reproduces in much the same way as animals such as cats, dogs, horses and tigers. A female and male come together and have sexual intercourse. A microscopic tadpole-shaped cell from the male joins with, or fertilizes, an egg cell from the female. This fertilized egg grows and develops in the womb of the female, into a baby ready to be born.

SEX ORGANS

          The parts of the body involved in reproduction are called the sex organs. They are present at birth, but they develop rapidly and start to work from the ages of about 11-14 years in girls and 13-16 years in boys. This time of rapid growth and changes in bodily features is known as puberty. A girl develops a more rounded body outline and her breasts enlarge. A boy grows facial hair and his voice breaks. These changes are controlled by hormones.

 

 

THE FIRST WEEK OF LIFE

          The egg cell (ovum) contains a set of genetic material from the mother. The sperm cell (spermatozoon) has a set from the father. When sperm and egg join, the fertilized egg contains the normal double-set of genetic material found in all body cells. The fertilized egg is larger than most cells, almost one-tenth of one millimetre across. But it divides many times by the process of cell division, so the cells reduce back to normal size. During this time the ball of cells passes along the egg duct to the womb.

          The womb lining has become thickened and rich with blood and nutrients, as part of the menstrual cycle. When the ball of cells reaches the inside of the womb, it burrows into the lining. The cells in the ball continue to multiply and the ball becomes hollow. A flatter, disc-shaped part appears in the middle of the hollow ball. As the cells multiply into many thousands and begin to move about, the disc changes shape into a tiny, tadpole-like object. This is a very young baby, called an embryo. It is hardly larger than a grain of rice, but its heart is already beating.

Picture Credit : Google

 

          The basic “building bricks” of the body are cells. There are over 200 different types, such as blood cells, nerve cells and muscle fibre cells. They vary greatly in size and shape, although most cells are far too small to see except through a powerful microscope. About 30 typical cells placed in a row would stretch only one millimetre. The whole body contains more than 50 million million cells. Most are in the blood and the brain.

INSIDE A CELL

          A typical cell is a bag of jelly, or cytoplasm, containing even smaller parts called organelles. Mitochondria are small and sausage-shaped. They break up substances such as sugar (glucose) to release energy for use in the cell. The cell’s skin-like covering, the cell membrane, allows only certain substances to pass in and out. The cell’s factory for making various substances and products is called the endoplasmic reticulum. The biggest organelle is usually the nucleus, a dark lump near the cell’s centre. It contains genes in the form of DNA.

          Genes contain all the information a living thing needs to develop, grow and maintain itself through life. A tiny worm has a few hundred genes. The human body has more than 100,000 genes. They determine whether you have dark hair, long legs, and a tendency to develop certain diseases, and so on.

          Genes are encoded like an “instruction manual” in DNA. The twisted-ladder shape of DNA is called a double helix. The rungs or cross-links are made of chemical sub-units, known as nucleotides. There are four: A, T, G and C (adenine, thymine, guanine and cytosine). A always forms a cross-link with T, and G with C. The order of sub-units A, T, G and C along the DNA is the genetic code, containing information for the genes in chemical form. Every body cell has a full set of DNA including all genes. But each cell uses only a tiny part of the DNA for its own life processes.

 

 

 

HOW DNA MULTIPLIES

          Cells do not live forever. Every minute the body makes about 3000 million new cells to replace those which naturally wear out and die. Also, reproduction involves making new cells. When a cell divides to make two new cells, its set of DNA is copied to make a duplicate set. Then each of the two new cells has a full DNA set with all the genes. DNA duplicates (copies) itself by breaking the cross-links that hold together its two strands. Each nucleotide sub-unit then joins to a new partner of its usual kind—A with T, and G with C. The row of new sub-units forms its own new strand. The result is two lengths of DNA, each identical to the other.

Picture Credit : Google

          The body has five main senses that detect what is happening in the outside world. Four are shown here. The fifth is touch, sensed by the skin.

SIGHT

          Each eyeball is about 25 millimetres across and well protected in a socket, called the orbit, inside the skull bone. Light rays enter the eye through its transparent domed front, the cornea. They pass into the eye through the pupil, a hole in a ring of muscle known as the iris. The iris makes the pupil smaller in bright conditions, to prevent too much light damaging the eye’s delicate interior. The rays are bent or focused by the lens, and shine a clear image on to the retina, which lines the rear of the eyeball. When light hits the retina, its 130 million microscopic cells make nerve signals, which pass along the optic nerve to the brain.

HEARING

          The curly flap of skin and gristle on the side of the head, which we call the ear, is simply a funnel shape for collecting sound waves from the air around. The waves travel along a slightly curved tube, the ear canal, and strike the ear drum, a small, thin piece of skin, which vibrates. The vibrations pass along a row of three tiny bones, the hammer, anvil and stirrup. The stirrup sends the vibrations into a snail-shaped part filled with fluid, known as the cochlea. The vibrations ripple through the fluid and shake microscopic hairs sticking out of nerve cells. When the hairs shake, the cells produce nerve signals, which travel along the auditory nerve to the brain.

TASTE

          The tongue’s upper surface is covered with many pimple-like lumps, known as papillae. These grip food to move it around while chewing. Scattered between the papillae are about 8000 taste buds. Each one has some 30 microscopic taste cells and looks like a tiny onion set into the tongue’s surface. When substances of a certain flavour in foods touch micro-hairs sticking up from the taste cells, the cells generate nerve signals which pass to the brain. Different tongue areas respond to different flavours.

SMELL

          In each side of the nose is an air chamber about as large as a thumb. Lining the roof of the chamber is a patch of 25 million smell cells. Each has more than 20 tiny hairs sticking from it. When certain odour substances touch the hairs, their cells send nerve signals to the brain. The nose can detect 10,000 different scents and smells.

 

 

HORMONES

          Two systems help the body’s parts and organs work together. One is the nervous system. The other is the hormonal or endocrine system, based on body chemicals called hormones. There are more than 50 different hormones. Each is made in a gland. Hormones flow around the bloodstream and affect certain cells, tissues and organs. They may cause them to work faster or slower, or release their products. For example, adrenaline from the adrenal gland makes the heart beat faster and more blood flow to the muscles, so the body is ready for action. The pituitary gland near the brain makes hormones that control other hormonal glands.

Picture Credit : Google

          Every thought and idea, every wish and want, every emotion and feeling, happens inside the brain. The brain fills the top half of the head, well protected within the domed skull bone. It looks like a large, wrinkled lump of pink-grey jelly. It contains some 50 billion nerve cells, or neurones. Each nerve cell is linked to many thousands of others. Tiny electrical nerve signals pass through this vast network, representing your thoughts and memories. Nerve signals also come into the brain from nerves all over the body, and go out to the muscles.

INSIDE THE BRAIN

          The brain has four main parts. The brain stem at the base tapers into the spinal cord. It controls automatic bodily activities such as heartbeat, breathing and digestion. The mid-brain just above has close links with the hormone system. One of its parts, the thalamus, controls the level of awareness, from wide awake and alert to drowsy or asleep. The third part is the cerebellum, a wrinkled lump at the rear. It deals with muscle control to make movements smooth and coordinated. The fourth part is the cerebrum, where thinking happens.

 

NERVE CELLS AND SIGNALS

           A nerve signal is a tiny pulse of electricity that travels very fast, almost 100 metres per second, along a nerve cell. A nerve cell has a normal-shaped cell body surrounded by thin, spidery parts called dendrites. It also has a very long, thin part like a wire, called the axon. Dendrites collect nerve signals from other nerve cells and pass them on, via the axon, to other nerve cells. Nerves contain bundles of hundreds or thousands of nerve cells.

          The brain’s thoughts, ideas and memories consist of nerve signals flashing to and fro around the unimaginably vast network of billions of nerve cells. New connections between nerve cells are constantly being made as old ones are lost. A new memory may form as a new pathway or route around certain cells. If you recall this memory often, you “refresh” the pathway and keep it active. If not, the memory fades.

 

 

 

THE NERVOUS SYSTEM

          The base of the brain merges into the spinal cord. The cord has nerve branches that reach out to everybody part, down to the fingertips and toes. The spinal cord carries nerve signals to and fro between the brain and all of these body parts. In addition, there are nerves that branch directly from the brain, into the head, face, neck and chest. These are cranial nerves.

Picture Credit : Google

          The 206 bones of the body make up its skeleton. Each bone forms a hard, rigid inner support for its part of the body, and anchorage points for muscles to pull as the body moves. The old bones of a museum skeleton are dry, brittle and crumbly. But inside the body, a bone is a very active, living part. It is not dry - it contains about one-fifth water. It is not brittle - it is slightly bendy because it contains fibres of a flexible substance, the body protein called collagen. Bone is also very tough because it contains hard crystals of minerals such as calcium phosphate. And like any other body part; a bone has a supply of blood vessels and nerves.

          Most bones are not solid. They are hollow, with a cavity inside. This contains a soft, jelly-like substance called bone marrow. The marrow makes new microscopic red and white cells for the blood at the rate of two million every second, to replace the old, dead blood cells.

 

 

 

 

TYPES OF JOINTS

          Bones are linked together at joints. In some joints the bones are fixed or cemented firmly to each other and cannot move, as with the small bones of the face. These are known as suture joints. In other joints the bones can move in relation to each other. The body has many different kinds of moveable joints, depending on the shapes of the bone ends and how they fit together. They resemble the joints used in machines to give a certain kind of movement. For example, the knee is a hinge joint and moves only backwards and forwards. The hip is a ball-and-socket joint and can move in any direction.

 

 

 

INSIDE A JOINT

             In a moveable joint the ends of the bones are covered with a smooth, shiny, slippery, slightly soft substance called cartilage. This prevents the bone ends rubbing against each other and wearing away. The cartilage surfaces slip over each other with hardly any wear. A flexible bag, the synovial capsule, wraps around the bone ends. This makes an oily fluid which fills the bag and lubricates the joint, like the oil in a machine. The two bones are linked by flexible, strap-like ligaments around the synovial capsule. These stop the bones coming apart and prevent the joint bending too much.

 

 

 

 

FRACTURES

          Bones are strong but sometimes they cannot withstand the stress put on them, especially in an accident. A bone may crack or snap. This is known as a fracture. In a compound fracture, the broken ends protrude through the skin. Part of the bone shatters into small parts in a comminuted fracture. The parts of the bone ram into each other in an impacted fracture.

Picture Credit : Google

 

 

          About two-fifths of the body’s weight is made up by its muscles—some 640 of them. Most are attached to the bones of the skeleton and pull on them to make the body move. In each part of the body the muscles are in two main layers. There are superficial muscles just under the skin and deep muscles lying below them next to the bones.

SKELETON

          The 206 bones of the skeleton form a strong inner framework for the rest of the body, which is soft and floppy. Different parts of the skeleton work in different ways. The skull is a domed protective case for the brain. The backbones, or vertebrae, are a strong yet flexible central support. The long bones of the limbs work like levers.

 

 

MUSCLES

          Every movement that the body makes is powered by muscles. A muscle is a body part designed to get shorter or contract. Most muscles are long and slim. They taper at each end into a rope-like tendon which is attached firmly to a bone of the skeleton. As the muscle contracts, it becomes thicker and pulls on the bone, moving that part of the body.

          The largest muscle is the gluteus maximus in the buttock. It pulls the thigh bone backwards at the hip when you walk and with greater speed and power when you run and jump. The smallest muscle is the stapedius, deep inside the ear. It is just a few millimetres long and thinner than cotton thread. It pulls on a tiny ear bone, the stirrup, to prevent very loud noises from damaging the delicate inner ear.

HOW MUSCLES WORK

          Each muscle is linked by nerves to the brain. The muscle itself is made up of bundles of hair-thin muscle fibres, which contain even thinner microscopic fibrils. In turn, each muscle fibril contains bundles of long, chain-like substances. These are muscle proteins, called actin and myosin.

          When you want to contract a muscle, the brain sends signals along the nerve to the muscle. The signals make the actin and myosin proteins slide past each other, rather like people pulling hand-over-hand on a rope. Each protein slides together only a fraction of a millimetre. But these tiny movements build up in the thousands of fibrils contained inside the hundreds of fibres. Most muscles can shorten to about two-thirds of their relaxed length.

 

MUSCLES IN ACTION

          Blinking your eye involves the movement of just one muscle, called the orbicularis oculi, an O-shaped muscle inside the eyelid. It is attached not to bones, but to other muscles and soft tissues. When it shortens, the two sides of the O move together and close the gap between them. The lip muscle, the orbicularis oris, works in the same way. Several other muscles in the face are not attached to bones. They pull on each other. This is how we make our huge range of facial expressions.

          Most muscles are attached to bones. They rarely work alone. They pull in pairs or teams, to make a bone move in a precise way. One bone may have 20 or 30 muscles attached to it, each in a different place and pulling in a different direction. This means different combinations of muscles can tilt and twist the bone in almost any direction, as when you turn your outstretched arm and hand from palm-up to palm-down.

          The body has different types of muscle in the walls of its inner organs, such as the intestines and bladder, and in the heart.

 

SKIN

          The largest part of the human body is its outer covering - the skin. This is like a flexible, all-over coat that protects the body from knocks and keeps out dirt and germs. It also keeps the delicate inner parts of the body moist and shields them from the harmful rays of the sun. Skin is at its thickest, five millimetres or more, on the soles of the feet. The thinnest skin, about half a millimetre, is on the eyelids.

         Skin gives the body its sense of touch. Millions of microscopic nerve endings just under the surface detect light touch, heavy pressure, heat, cold and pain. The skin grows hairs from tiny pits called follicles. There are about 120,000 large hairs on the head and four million tiny hairs over the rest of the body. Skin also sweats and increases the amount of blood flowing through it, to keep the body cool in hot conditions.

Picture Credit : Google

 

          All the muscles and tissues that make up the body must be continually supplied with food and oxygen. This job is carried out by the blood circulatory system.

          The heart lies at the centre of the circulatory system and pumps the blood around the body. About the size of your fist, it is an incredibly strong organ, made entirely of muscle. It beats more than two billion times during the average life span of a person and pumps about 340 litres of blood every hour—enough to fill a car’s petrol tank every seven minutes.

          Blood containing fresh oxygen travels from the lungs to the heart through the pulmonary veins. At the same time, blood with very little oxygen left in it returns to the heart along veins from the muscles and tissues. The heart pumps the fresh blood to the rest of the body and the exhausted blood to the lungs. It pumps the blood at high pressure so that it can travel upwards to the head—against gravity—as well as downwards. You can feel this pumping action by placing your fingers on the inside of your wrist or the side of your neck, both points where a main artery lies close to the surface of your skin.

 

 

BLOOD

          Pumped by the heart, blood collects oxygen from the lungs and dissolved food from the liver and delivers it to all parts of the body. It also clears away waste, helps cool the body when it overheats, clots when the skin is damaged and protects against invading bacteria and viruses.

          The veins and arteries in your body look like a page in a road atlas. There are motorways, the main blood-carrying tubes or vessels, which lead out from the heart to the limbs and the head. There are also lanes and tracks, tiny vessels called capillaries that reach all the cells in the body.

 

 

          Blood is made up of millions of tiny cells floating in a yellowish, watery fluid called plasma. There are red cells, used for carrying oxygen, white cells, which fight any infection by invading bacteria or viruses, and platelets, which make the blood clot when a vessel is damaged, so sealing the wound. Different kinds of white cell work together to protect you from disease: T-cells, which identify invaders; B-cells, which make deadly proteins called antibodies that surround the invaders; and macrophages, which swallow them up and destroy them.

Picture Credit : Google

 

          The body needs continual supplies of oxygen. This invisible gas makes up about one-fifth of the air around us. It is needed for chemical processes inside the body’s cells that release energy from food. Breathing draws air into the body so that oxygen can be absorbed.

RESPIRATORY SYSTEM

          The respiratory system draws fresh air into the body, absorbs the vital oxygen from it into the blood, and then passes the stale air out again. The main parts of the system where oxygen is absorbed are the lungs. Breathing muscles stretch the lungs to make them larger and suck in air. These muscles are the diaphragm below the lungs, and the intercostal muscles between the ribs. Fresh air passes in through the nose and mouth, down the pharynx (throat) and trachea (windpipe), into the lungs. The lung airways, called bronchi, divide many times and become thinner, ending in terminal bronchioles, narrower than human hairs.

          Each terminal bronchiole ends in a cluster of microscopic air bubbles, called alveoli. There are about 300 million alveoli in each lung, giving the whole lung a spongy texture. Besides fresh air, the lungs also receive low-oxygen blood from the heart along the pulmonary arteries. These divide and form networks of microscopic blood vessels (capillaries) around the alveoli. Oxygen from the air inside the alveoli passes easily through the thin walls of the alveoli and capillaries into the blood. This high-oxygen blood returns along pulmonary veins to the heart.

CLEANING THE LUNGS

          The lungs are delicate and easily damaged. Hairs in the nose filter bits of floating dust and other particles from air as it is breathed in. The airways are lined by sticky mucus which traps dirt and dust. Microscopic hairs, called cilia, line the smaller airways. They sweep mucus and trapped dirt into the throat, where it can be swallowed.

SPEECH

          Air emerging from the lungs not only carries waste carbon dioxide. It has another use—speech. At the top of the trachea is the larynx (voice box). This has a shelf-like fold of cartilage projecting from each side, known as the vocal cords. To speak, muscles pull the vocal cords together so that there is only a very narrow slit between them. Air rushing through the slit makes the cords shake or vibrate, which produces sounds. These sounds are shaped into clear words by movements of the mouth, cheeks, teeth, tongue and lips.

 

BREATHING RATE

          As oxygen passes from the air in the alveoli into the blood, the waste substance carbon dioxide passes the opposite way, from the blood into the air. This stale air is then pushed out of the lungs when the breathing muscles relax and the stretched lungs spring back to their smaller size. At rest, an adult person breathes in and out about 12 times each minute. Each breath is around half a litre of air. After running a race, a person may breathe 60 times each minute and take in more than two litres of air each time, to obtain extra oxygen for the active muscles.

Picture Credit : Google

 

 

          The entire digestive system, from the mouth to the anus, is about nine metres long. Looped and coiled into the lower abdomen, the small intestine makes up two-thirds of this length. Digestive juices from the small intestine’s lining are added to the food to complete its chemical breakdown. The resulting nutrients are so small that they can pass through the lining into the blood, to be carried away to the liver. The liver acts as a kind of food processor, making new chemicals from the nutrients it receives and storing them until they are required. Those substances the body does not need, including impurities in the blood, it sends on to the kidneys.

THE KIDNEYS

          The two kidneys receive a very large flow of blood—more than one litre per minute. It passes through about one million microscopic filtering units, called nephrons, packed into the outer layer of each kidney. The nephrons remove waste substances and excess water from the blood. These flow through the kidney’s inner layer, where some water is taken back into the blood according to the body’s needs. The resulting liquid waste is called urine. It dribbles down a tube, the ureter, to a stretchy bag in the lower abdomen, the bladder. It is stored here until it can be passed to the outside.

 

NUTRIENTS

          The body needs a wide range of nutrients to stay healthy. There are six main groups of nutrients—proteins, fats, carbohydrates, vitamins, minerals and fibre. Different kinds of foods are rich in different groups. Proteins are found in meat, poultry, fish, milk, beans and green vegetables. They help to build and maintain muscles and other body parts, so they are important for growth. Fats (lipids) are found in meat, dairy products, pies, and some oily fruits and vegetables like avocado, olive and sunflower seeds. Small amounts are needed to build the walls around the body’s microscopic cells, and also for healthy nerves. Carbohydrates such as starches and sugars are found in bread, pasta, rice and other grains, and potatoes. They are the main source of energy for movement, digestion and other life processes.

 

 

 

VITAMINS AND MINERALS

          Many vitamins and minerals are needed for good health, but usually in small amounts. Vitamins have letters such as A, B and C. Lack of a vitamin may cause illness. For example, lack of vitamin A from tomatoes, carrots, cheese, fish and liver may result in poor eyesight. Minerals include calcium and iron. Iron is found in meat, green vegetables and nuts. It is needed for healthy blood. Its lack causes a type of anaemia.

 

FIBRE

          Fibre is found only in plant foods, chiefly in breads, pastas and other products made from whole meal grains or cereals, and also in many fresh fruits and vegetables. Fibre is not actually digested and absorbed by the body, but it helps the digestive system to work effectively and stay healthy. It adds bulk to the food so that the stomach and intestines can grip and squeeze the food along.

 

Picture Credit : Google

 

 

         

 

 

                    The body needs energy to power its chemical life processes. It also needs raw materials for maintenance, growth and repair. The energy and raw materials are in our food. Digestion is the process of taking in, or eating, food and breaking it down into tiny pieces, small enough to pass into the blood and be carried all around the body. The parts that take in and break down food are known as the digestive system.

 

 

 

 

 

 

 

 

 

INSIDE THE MOUTH

                     The teeth cut off and chew pieces of food into a soft pulp. Saliva (spit) makes the food moist and slippery, for easy swallowing. The tongue tastes the food, to make sure it is not bad or rotten, and moves it around in the mouth, for thorough chewing. The lips seal at the front of the mouth to stop food and drink dribbling out during chewing.

 

 

 

 

TEETH

                     There are four main kinds of teeth. The sharp-edged, chisel-like incisors at the front of the mouth slice and cut pieces from large food items. The taller, pointed canines tear and rip tough food. The premolars and molars at the back of the mouth squeeze and crush the food. Each tooth has a long root that fixes it firmly in the jaw bone, and a crown that sticks up above the soft, pink gum. The whitish enamel covering the crown is the hardest substance in the body.

 

 

 

 

 

 

OESOPHAGUS AND STOMACH

               Swallowed food is squeezed down the oesophagus by wave-like muscular contractions of its wall, called peristalsis. The food enters the stomach, a J-shaped muscular bag. This expands like a balloon to hold about three litres of food and drink. It churns up the food, mixing in its strong digestive juices to break it into smaller and smaller particles. An average meal takes between three and six hours to be digested in the stomach. If the food is bad or unsuitable in some way, peristalsis works in reverse and pushes it up and out of the mouth, a process called vomiting.

                  Two large organs aid the process of digestion. The pancreas gland is wedge-shaped and lies behind the stomach on the left. It makes strong digestive juices that flow along a tube, the pancreatic duct, into the small intestine. These juices dissolve the food further. The other organ is the liver, in front of the stomach on the right. It makes a yellow-green liquid, bile. This is stored in the gall bladder and then added to the food in the small intestine, to help digest fatty foods.

Picture Credit : Google

          The Human Body is the most studied object in all of science. Yet every year we learn even more about its most detailed structures and its innermost workings. Even in ancient times people have known basic facts—for example, that there are 206 bones in its skeleton. Since the invention of the microscope nearly 400 years ago, people have studied the body’s billions of tiny building blocks, known as cells. In more recent years we have learned about the instructions or “blueprint” for making the body—its genes.

 

ORGANS AND SYSTEMS  

         The body’s main parts, like the brain, heart, lungs and stomach, are called organs. Different groups of organs work together as systems. Each system has a vital job to keep the whole body alive and healthy. For example, the heart, the body-wide network of tubes, called blood vessels, and the red liquid called blood, together form the circulatory system. This carries essential nutrients and oxygen to all body parts and collects waste materials for disposal. There are about a dozen major systems.

Picture Credit : Google