Category Human Body

Why do I have nails?

                      You need nails to provide a firm support for the sensitive skin on the fingertips. If you cut your fingernails too short you will notice how difficult it is to pick up small objects. Nails grow continuously from an area called the nail bed, or quick. Because your nails are transparent, you can see right into the tissue below the nail, which is always pink because it contains blood. Nails grow at a rate of about 0.1 mm per day. They are made of keratin, the same material as hair. Because nails are  not living material, they do not hurt when you cut them.

What are freckles?

                    Freckles are patches of melanin that are concentrated together instead of being spread evenly throughout the skin. Some people with very fair skin and lots of freckles do not tan evenly. They are particularly likely to develop sunburn unless they protect themselves from the Sun.

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Why do I have hair?

                           Hair originally helped prevent heat loss from the body. It no longer has that function although it does help to protect your head. Each hair grows from a pit in the skin called a follicle. The hair itself is made of a tough material called keratin, and it grows continuously from the follicle. The hair shaft contains pigment that gives the hair its colour. In older people, air may enter the hollow hair shaft, making it look grey.

Why is some hair curly?

                   Hair is straight or curly depending on the shape of the follicle from which it grows. Straight hair grows from completely round follicles, while wavy hair comes from oval follicles. Very curly hair grows from flattened follicles.

Why do some people go bald?

                       A substance called testosterone affects hair growth in men. It is responsible for the tough facial beard grown by men. Changes in testosterone levels affect the amount of hair growing on a man’s head.

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 How does skin tan?

                       Skin develops extra melanin when it is exposed to strong sunlight. Tiny grains of melanin are produced in the skin cells and spread to produce an even suntan, which helps to protect against Sun damage. This even happens in people with naturally dark skin. You can get sunburn if you are exposed to the Sun’s rays for too long, because the damage will be done before the protective melanin can develop. You should always use protective sun cream and limit the amount of time you spend in the sunshine.

How do cuts and grazes heal?

When you cut or graze yourself, the blood clots to prevent bleeding. Clotting is caused by substances in the blood. Together with small particles called platelets, these substances produce masses of fine fibres when they are exposed to air. They block the wound and prevent more blood loss. New cells grow rapidly into the wound, replacing the damaged tissue. Soon the clotted material, called a scab, falls off and clean, new skin is revealed underneath.

Why does the body have skin?

                Skin is a flexible, waterproof covering that protects us from the outside world. It prevents harmful germs from entering the body. Skin is your largest organ, and it is sensitive to touch, temperature and pain. Your skin tells you what is happening around your body, so you can avoid injuring yourself. Also it helps to prevent damage from the Sun’s harmful ultraviolet rays. Skin also helps to regulate body temperature by sweating and flushing to lose heat when you get too hot.

Is skin alive?

              All the skin cells that you can see are dead! Your body is constantly producing new skin cells from beneath the surface skin layer that you can see. As new cells push upwards towards the surface, the older cells on top become flattened and eventually die. The dead cells form a protective layer that constantly flakes away like dust.

Why do people have different skin colours?

                    Skin colour is caused by a dark pigment called melanin in cells below the skin’s surface. Melanin filters out harmful ultraviolet light from the Sun, preventing damage to the tissues beneath the skin. People originating from hot countries have developed extra melanin in their skins for Sun protection, so their skin is darker.

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Why do people sweat?

                    Sweating removes excess salt and wastes through the skin. It also helps to keep you cool, because sweat takes heat away from the body as it evaporates on the skin. If you have been exercising and are very sweaty, and then stand in a draught, you will notice this cooling effect very quickly. Sweat is a watery liquid, but other skin glands release an oily substance called sebum that helps to lubricate the skin and keep it supple.

Why do I need to sleep?

            You spend about one-third of your life asleep, but no one is sure why this is necessary. During deep sleep, the body produces large amounts of growth hormone that help to repair or replace damaged cells and tissue. Sleep also speeds healing. While you are sleeping, the brain remains very active. The body goes through stages of being very limp and relaxed and other stages when the eyes move about beneath closed eyelids. Dreaming takes place during this rapid eye movement period, called REM sleep. Dreaming is very important. If you prevent someone from dreaming by waking them every time they enter REM sleep, that person can become very disturbed and ill after several dreamless nights.

How does the body repair damaged tissues and cells?

Cells are able to divide very quickly to replace those that are old or have died. Nerve cells are the only ones that cannot be replaced. However, even nerve cells can sometimes grow new connections if the long fibres along which messages are passed become damaged. Dead and dying cells are removed by white blood cells in the blood stream, which actually eat them. The liver is also able to break down red blood cells, which are only able to survive for a short time.

What job do the kidneys do?

                  Kidneys are very effective at removing most of the waste from our blood.

                   Blood is pumped through groups of tiny tubes inside the kidneys, and harmful waste material passes out through the walls of these vessels and down a long tube called the ureter, into the bladder. Here it is stored until ready to be discharged from the body as urine. The kidneys have a very important function in controlling the amount of water in the body. Water balance needs to be kept at exactly the right level if the body cells are to remain healthy.

 What is a kidney machine?

If the kidneys become diseased and stop working, it is necessary to use a kidney machine to remove waste from the blood. This machine process is called dialysis. It involves pumping blood from a tube in the person’s arm into thin tubing that runs through a tank of sterile liquid. Waste passes from the blood through the walls of the tubing, and the cleaned blood is returned to the body. This has to be done throughout the person’s life, unless a new kidney can be provided in a transplant operation. Dialysis needs to be carried out frequently — several times a week — to stop wastes from building up to dangerous levels.

How does the body keep at the proper temperature?

The body has several systems to keep itself at the right temperature. Heat is produced by the breakdown of food substances stored in the body. The chemical reactions in the body will only take place properly if the body is kept at the ideal temperature, so any extra heat has to be removed. Heat leaves the body through the lungs, as you breathe out warmed air, and also through the skin. If you are very hot, the blood vessels near the skin’s surface open wider to increase the blood flow, so you look a bit pink. The extra blood means more heat leaves the skin surface, so cooling your body.

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