Ouch! Nerves give us our sense of touch. T at means they let us feel pain, too. It may sound strange, but feeling pain helps you stay healthy. T ink about a paper cut, for example. T e
edge of a sheet of paper hits your skin at just the right angle. It slices through the epidermis and into the dermis. T e paper touches nerve endings. Ouch!
You feel the pain and jerk your fi nger away before the cut goes deeper. T is pain lets you know you have an injury that needs attention.
Invaders Beware T e cut will bleed a bit. T at’s because the paper breaks through tiny blood vessels in the dermis. T is may sound strange, too. But bleeding can help you stay healthy. Here’s why. T e cut is not just a pain. It’s now a way
for harmful germs to get into your body. Your body sees the germs as invaders. Your blood comes to the rescue. It has
special fi ghter cells in it. T ey attack and destroy the germs. T e skin around the injury swells and gets red. T e red, swollen skin is a sign that your body is fi ghting the germs.
Keeping Cool T ese blood vessels also help keep you the right temperature. If you get too hot, they expand. More blood fl ows through your skin. Heat can escape your body. If you get too cold, the blood vessels shrink. Blood fl ow slows and more heat stays in your body. T e dermis is full of other structures, too.
It has glands. Glands are tiny organs. T e glands in your dermis make sweat. T is salty liquid helps keep your body from overheating. Sweat leaves your body through small
holes, or pores, in the surface of your skin. As the sweat evaporates into the air, it cools you and your body. Other glands in your dermis make an oil. It waterproofs your skin. T at way, you don’t get too soggy. T is is just one more way your skin keeps you healthy.
22 NATIONAL GEOGRAPHIC EXPLORER
Extra Padding Beneath the dermis is the last layer. T is layer protects the organs inside your body. It’s your hypodermis. It’s mostly made of fat and acts like a cushion. T e hypodermis absorbs the shock of all the little hurts your body takes every day. T e thickness of this layer varies. You have
a good amount of fat on your belly and upper legs, for example. You have very little fat on your eyelids. Some animals have super thick layers of
fat in their hypodermis. It’s called blubber. In seals, blubber can make up half an adult’s body weight. T ey need this layer to keep warm in cold water. Blubber is also used as a source of energy when food is scarce.
A thick layer of blubber helps keep this seal warm.
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