The whole body is covered with skin.The surface of the skin is dead(like the hair and the nails),but it is made from a living layer(层)just under the surface.The outside dead layers wear off(磨损)all the time,with new ones replacing them,and the body forms a totally new skin every three weeks.
The skin protects the body from the outside world and it passes information from the outside.It helps to keep water in the body and to keep the body at the same temperature.Becteria(细菌)can’t get in through the skin unless it is damaged.
If the weather is cold,the blood vessels(血管)in the skin squeeze down,or contract(收缩),so that as little blood as possible comes near the surface.This means that less warmth is lost to the outside.This makes the skin look pale,or even “blue”.At the same time,the hairs on the skin are pulled upright by tiny muscles.
When it is hot,the blood vessels expand(扩大),or get wider again,to allow plenty of blood to run near the surface of the skin.This helps the body to lose heat,and the skin may look red.At the same time,the sweat glands(汗腺)produce more sweat,which cools the skin.
If your skin has ever been numb(麻木的),you will realize how important the feeling from the skin is.Nerves(神经)in the skin are sensitive(敏感的)to heat and cold,sharpness,hardness and softness,wetness and dryness and pain.If one is not able to feel these things,which can act as warnings,he is likely to be burned,cut or hurt in other ways.
The colour of the skin depends on special colour cells(细胞).These are just below the top layers of the skin.They are needed as protection from some harmful ray of the sun.The stronger the sun is,the more important it is to have a dark skin.People with pale skins may “tan”(晒黑)in the sun.This happens when the body produces extra colour cells in the skin for protection.In the sun,the skin produces a vitamin(vitamin D)which is needed for strong bones.
小题1:Which of the following statements is NOT true?
A．Our hair and nails are dead like the surface of the skin.
B．There is skin all over our body.
C．The skin of our bodies will be completely different in three weeks.
D．The surface of the skin is made of a living layer.小题2:The second paragraph mainly tells us about______.
A．the functions of the skin
B．the information from the outside
C．the water in the body
D．the temperature of the body小题3:Bacteria will get in through the skin______.
A．when one’s skin is numb
B．when one is ill
C．when the skin is cut
D．when the sweat glands produce more sweat小题4:When the weather is cold,the skin will contract in order to______.
A．allow more blood near
B．make the skin look blue
C．keep warmth
D．help the body lose heat小题5:The colour of the skin is determined by______.
A．the rays of the strong sun
B．colour cells
C．top layers of the skin
D．vitamin D
