Ouch! Nerves let you feel pain. T is is a good thing. Ever cut your finger? Ouch! You feel pain. You jerk your finger away. T is pain is an alert. It tells you the injury needs attention. T e cut breaks blood vessels in the dermis. You start to bleed.


Blood to the Rescue Germs can enter your body when a cut starts bleeding. Your body needs to fight off the germs. First, the skin around the injury


swells. It gets red. T at’s a sign your body is fighting the germs. Next, blood moves through your


body to the place where you were cut. T e blood moves quickly through blood vessels to reach the injury. T en, special cells in your blood


attack the germs. Some of the cells gobble up the germs. Other cells punch holes in the germs. Blood vessels work with your skin


in other ways, too. If you get too hot, blood vessels get wider. T is lets more blood fl ow and gives off heat. T en you feel sweat on your skin. Blood vessels shrink if you get too


cold. T e fl ow of blood slows down. More heat stays in your body.


22 NATIONAL GEOGRAPHIC EXPLORER


Extra Padding T e last layer of skin is under the dermis. It’s your hypodermis. T e hypodermis is like a fatty cushion. It protects the organs inside your body. It also protects you from all the little bumps and bruises your body takes every day. Some animals, like seals, have a


thick hypodermis. It’s called blubber. Blubber keeps seals warm.


A thick layer of blubber helps keep this seal warm.


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