My Science School

 

 

What happens after fertilization?

                    The fertilized egg begins to divide as it travels down the fallopian tube towards the womb. By the time it enters the womb it has divided into a ball of about 100 cells. It settles on the wall of the womb and sinks into the surface, becoming firmly fixed. At this point, the female is pregnant.

 

 

 

 

What is an embryo?

                     For the first eight weeks of a pregnancy, the developing egg is called an embryo. A liquid-filled bag develops around the embryo to protect it. By the fourth week of pregnancy the embryo is the size of a grain of rice. It has a head and a tail, and the beginning of limbs, and its tiny heart begins to beat. The placenta is the embryo’s life-support system. It is a red, flattened organ that becomes deeply embedded in the wall of the womb. The placenta extracts food substances from the mother’s blood and passes waste material from the embryo back to the mother for disposal. The placenta is connected to the developing baby by a thick umbilical cord, which contains large blood vessels.

 

 

 

What is a period?

                          Each month, an egg cell is released from a female’s ovaries. When this happens, the lining of the womb changes so that it is ready to receive the egg if it is fertilized.

                           If the egg is not fertilized, the womb lining breaks down, and blood and tissue pass out through the vagina. This process is called a period, and it happens about every 28 days. The time from one period to the next is known as the menstrual cycle. Hormones from the pituitary gland and the ovaries control the menstrual cycle, which may he irregular. However, it usually settles into a regular cycle.

 

 

 

How does fertilization take place?

                         It takes two days for an egg cell to travel along the Fallopian tube. During this time it may be fertilized. The male’s penis places sperms in the vagina, and about 300 million sperms are released. Some sperms pass through the neck of the womb and swim up into the uterus. They enter the Fallopian tube where some will meet the egg. Only one sperm may wriggle inside and fuse its own nucleus with the nucleus of the egg.

 

 

 

 

What is contraception?

                       Contraception prevents fertilization from taking place. There are several different contraceptive methods. One method involves a contraceptive device called a condom. It is a rubber covering, or sheath, that is worn over the penis to stop the escape of sperms. The contraceptive ‘pill’ is a drug taken regularly by a female. It prevents the ovaries from producing ripe eggs, or stops the eggs from developing.

 

How are sperms made?

                        Sperms, the male sex cells, develop in the testes. They are stored for several days until needed. The testes contain long tubes called the seminiferous tubules, which are tightly coiled. Sperms are produced continuously in these tubes, then passed to the epididymis and stored in a large duct called the vas deferens. Here liquid is added to the sperm to make a milky fluid called semen. It is stored in pouches called seminal vesicles. During sexual intercourse the seminal vesicles contract and force out the sperm. It passes out of the penis and into the female sexual organs.

How many sperms are there?

                     Up to 100 million sperms are produced every day by the male. If they are not released, they are soon destroyed and replaced. Sperms look like tiny tadpoles, with rounded heads and long lashing tails. They use their tails to swim at a speed of about one cm per minute. The head of the sperm contains the nucleus, which will join with the egg cell during fertilization.

 

 

What is a human egg cell?

                         The ovaries of a newborn baby girl contain about 250,000 egg cells. By the time she reaches maturity, there will be about 10,000 remaining. However, only a few of these eggs will be used — one each month throughout the years when she can have a baby. Every 28 days, a swelling appears on an ovary. This releases the egg cell in a process called ovulation. The egg cell then enters the fallopian tube. The swelling it emerged from produces hormones to prepare the womb to receive the egg.

 

 

What are the female sex organs?

                        The female sex organs are inside a woman’s lower abdomen. The womb, or uterus, is a pear-shaped muscular organ from which two ‘horns’ run out sideways, ending with the Fallopian tubes. The neck of these tubes is funnel-shaped, and the funnels are cupped around the ovaries where the egg cells are produced. The neck of the womb leads to a short tube called the vagina, leading outside the body. Urine passes out through a short tube, the urethra, near the mouth of the vagina.

 

 

 

What are the male sex organs?

                         The male sex organs are the testes and the penis. The two testes are contained in a skin sac called the scrotum, hanging beneath the groin. A tube called the urethra, which is connected to both the bladder and the testes, runs through the middle of the penis. The urethra is used to pass urine and also, at a different time, to pass sperms out of the man’s body. During intercourse the penis becomes stiff as blood is pumped into a cavity called the corpus cavernosum.

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Which gland helps with digestion?

                         The pancreas is an important gland that helps with digestion. It also controls sugar levels within the body. The pancreas produces digestive enzymes that flow into the intestine during the process of digestion. The pancreas also functions as an endocrine gland, releasing the hormone insulin into the blood. Insulin helps the body’s cells to use glucose, which is essential in the production of the energy that powers cells.

 

 

 

Which hormone affects growth?

                        Growth hormone, one of the most powerful hormones in the body, is produced in the pituitary gland. Growth hormone causes growth throughout childhood and adolescence, and it also affects the way that food substances are used to build new tissues. It stimulates cells throughout the entire body, and also causes the liver to produce special substances that activate bone and muscle growth.

                        Growth hormone is produced in differing amounts during adolescence, which is why children have a series of ‘growth spurts’ when they grow very rapidly. In adults, growth hormone acts mainly to maintain and repair the tissues.

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What is diabetes?

                     Diabetes is an illness that is caused when the body does not produce enough insulin. The result is that large amounts of glucose build up in the blood and the person has to urinate frequently to get rid of it. At the same time the loss of fluid makes the person very thirsty. A diabetic person may lose weight, because the body breaks down body fat when it cannot get energy from glucose, Sometimes the insulin shortage can be corrected by drugs or, in the case of severe diabetes, by having regular insulin injections of insulin.

 

 

What happens when I am frightened?

                        When you are frightened, hormones help to prepare you to fight or to run away. This is a primitive reaction that all human beings still have, and it can affect our day-to-day behaviour. A hormone called adrenalin is released from the adrenal glands, which are small glands attached to the kidneys. Adrenalin readies the body for instant action. It makes your heart beat faster and you breathe more deeply. The increased blood flow releases energy from the stored food materials, ready to provide power for the muscles to work.

                        Adrenalin causes the pupils of the eye to open wider, improving vision. Also, it makes digestive processes stop, allowing energy and blood to be channelled to other important areas. Blood is channelled away from the skin, so you become pale, and tiny muscles in the skin contract making your hairs stand on end, causing ‘gooseflesh’.

 

 

 

Which is the ‘master gland’?

                   The pituitary gland, in the base of the brain, is the most important endocrine gland. Although it is only tiny, it produces hormones that regulate the effects of the other glands. The pituitary gland is connected directly to a region of the brain called the hypothalamus, and so provides the link between the brain and the endocrine system. The pituitary gland produces many important hormones, including growth hormone as well as hormones that cause the sex glands to start secreting their own hormones.

 

 

 

Which gland controls the way the body uses energy?

                           The thyroid gland produces hormones that control the rate at which chemical reactions take place in the body. The gland is in the base of the neck. Thyroxin is one of the hormones produced by the thyroid gland. It speeds up the production of energy from the food you eat. An underactive thyroid can mean that a person becomes slow and sluggish. Other hormones from the thyroid control the amount of calcium in the bones.

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What job do hormones do?

                       Hormones are chemical messengers that are produced in one part of the body and have an effect on another part.

                       Hormones switch body processes on and off, and they regulate most of the body’s activity. The nervous system also helps in these processes, giving rapid instructions along the nerves. The body’s endocrine system uses hormones which work much more slowly. The majority of hormones are carried around the body in the bloodstream, reaching all the major organs and tissues.

 

 

 

 

 

How many hormones does the body have?

                        The body has more than 30 different hormones. They are mostly produced in organs called endocrine glands.

                       These glands discharge the hormones directly into the bloodstream. Other types of glands pass their secretions through ducts to the point where they are needed. Endocrine glands are found in the head, neck and torso. The amount of hormones in the body is regulated by a feedback system. This means that once hormones are produced, the body measures them and once they have reached the required level, their production is switched off again. Sometimes this mechanism does not work properly, and over or underactive glands such as the thyroid can produce illness.

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How are invading germs destroyed?

                        Special T-lymphocytes attach themselves to any invading organisms and destroy them. The T-lymphocytes release special substances that attract another type of white blood cell which consumes the invaders. B-lymphocytes are also stored in the lymph system. They release a flow of substances called antibodies. These lock on to invading organisms. Each antibody attacks a particular type of invader, clumping them together so they are destroyed by the white blood cells. When a new infection is found, the B-lymphocytes make an antibody to attack it.

 

 

 Can our bodies attack themselves?

                         Sometimes the immune system mistakes some harmless material for an invader and this can cause illness.

                         Grass pollen and dust are harmless materials that are often inhaled. In some people the body mounts a fierce attack on them. The immune system releases the substances normally designed to fight infection, and their effects can cause illnesses such as hay fever and asthma. Sometimes the immune system attacks normal tissue or organs, causing a condition called auto-immune disease. This can produce serious illness, but fortunately it is quite rare.

 

 

 

 

 

Why can the body reject a transplant organ?

All your body cells carry a ‘label’, or marker substance, on the outside of the cell. This marker is recognized by the immune system, which will not attack it. In some very serious illnesses, when a person’s organ has failed completely, an organ from another individual may be transplanted. The donated organs carry different marker substances, so the immune system treats them as invaders and will mount an attack on them called rejection. These attacks from the immune system can be reduced or prevented by the use of powerful drugs.

 

 

Why do hot foods taste better?

                    Hot foods taste better because the heat causes more of the pleasant smells to rise into the nose. These abundant smells contribute to the total taste of the food.

 

 

 

 

How does the sense of smell work?

                     The sense of smell is probably the oldest of our five senses. As you breathe in, air passes through a cavity behind the nose. It contains patches of millions of smell receptors called olfactory cells. Sensory hairs stick out from the surface of these receptor cells. The hairs detect smells and pass information along nerve fibres to the brain. Substances that you recognize as having an odour dissolve in the layer of mucus covering the sensory cells, stimulating them to produce a signal.

                   Most people are able to detect about 4,000 different smells. However, people whose work is based on their ability to smell, such as chefs, perfume makers and wine tasters, can distinguish as many as 10,000 different smells.

 

Is smell and taste the same?

                   The taste of food is a mixture of both taste and smell. As you eat, tiny food particles drift up into the nasal passages from the back of the mouth. The smell of the food contributes to the simple tastes detected by the tongue. This explains why food tastes odd when the nasal organs are inflamed or covered by thick mucus when you have a heavy cold — the sense of smell is temporarily smothered. When you eat very spicy foods, such as curry or chilli, mild pain also forms a part of the characteristic taste. If these foods did not burn the mouth, they would not taste like curry or chilli at all. If we were to lose our sense of smell, almost all taste sensation would be lost as well. This means that we would not enjoy the taste of our food nearly so much.

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How do pain-killing drugs work?

                 Pain-killing drugs, or analgesics, work in two different ways. Some drugs, such as aspirin, work by preventing the sensation of pain from reaching the brain. More powerful pain-killing drugs prevent the brain from reacting to the nerve impulses that it receives from pain receptors.

 

 

 

 

 

What is a phantom limb?

                     When a damaged limb has to be removed surgically, a person may feel as though the limb is still attached to the body. This happens because the nerves that once led from the limb are still in place. They keep producing nerve impulses that trick the brain into thinking that the limb is still part of the body.

 

 

 

 

How do we taste things?

                      Most of the sense of taste takes place on the tongue. The tongue is covered with small bumps, called taste buds that are grouped together in areas with different functions. These taste buds react to some simple tastes and pass messages to the brain. Taste buds on the tip of the tongue detect sweet tastes, and those at the back of the tongue detect bitter taste (the ‘aftertaste’ you get after swallowing something bitter). Groups of taste buds at the side of the tongue measure sour and salty tastes. The taste of any food is a combination of these four basic tastes. You have about 10,000 taste buds on your tongue. You will gradually lose them as you grow older, which is one reason why elderly people may no longer enjoy their food so much.

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How does the sense of touch protect the body from injury?

                    Your skin continuously passes huge amounts of information to the brain. It monitors touch, pain, temperature and other factors that tell the brain exactly how the body is being affected by its environment. Without this constant flow of information, you would keep injuring yourself accidentally, which is what happens in some rare diseases where the skin senses are lost.

                    Sensations in the skin are measured by tiny receptors at the ends of nerve fibres. There are several different types of receptor. Each type can detect only one kind of sensation, such as pain, temperature, pressure, touch and so on.

 

 

Why are some parts of the body more sensitive than others?

Receptors are grouped together according to the importance of their function. There are large numbers of receptors in the hands and the lips, for example, where the sensation of touch is very important. Receptors are present in much smaller numbers over other parts of the body, which are less sensitive to touch, for example, on the back.

 

 

What happens if the immune system doesn’t work?

                       Very rarely, a baby is born without a proper immune system. It will have no resistance to infection. When this happens, the baby has to live in a plastic bubble from which all germs are kept out. Sometimes the immune system recovers as the child grows, so they can be released from the bubble.

 

 

How are babies protected from infections?

                        A newborn baby is protected from infection by antibodies that were present in its mother’s blood. The mother’s blood contains antibodies to the infections to which she has become immune during her life. These antibodies are transferred to the baby’s blood via the placenta that nourished the baby in the womb.

                       The antibodies continue to protect the baby for several weeks, while its own immune system develops and begins to work property. This period of protection is increased if the mother breast feeds her baby, as her milk will also contain these antibodies. Bottle fed babies do not have this natural immunity.

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Why is AIDS such a serious illness?

                          AIDS is a unique disease because it attacks the immune system that is intended to defend the body against infection. The HIV virus that causes AIDS destroys lymphocytes so the body cannot fight off infection. The HIV virus does not cause the symptoms of the disease, but the body is now defenseless and can be attacked by other disease organisms. Some powerful drugs can now delay the destructive effects of infection by the HIV virus.

 

 

 

 

 

 

 

 

 

 

What are bacteria and viruses?

Bacteria and viruses are the most important causes of disease. Bacteria are simple plant-like organisms that can divide very quickly. They cause many common infections such as boils and acne. Viruses are very much smaller, and technically they are not alive at all. They can take over the functioning of an infected cell and turn it into a factory producing millions more viruses. Viruses are responsible for many common diseases such as colds and influenza.

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What is the immune system?

Unlike most of the other body systems, the immune system is scattered throughout the body. The main defence against invaders such as bacteria and viruses are white blood cells called lymphocytes. These blood cells are made and stored in the body’s lymphatic system, which is a network of thin tubes running throughout the body. It contains watery liquid called lymph, which it drains from the tissues and returns to the blood. At intervals along the length of the lymph vessels are small lumps called lymph nodes. Lymphocytes are stored in these lymph nodes. Waves of lymphocytes are released when the body is injured, or when invaders are detected, and the lymphocytes swarm to the damaged area.

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