Theo Baker - Human Bodies

Theo Baker

rourkeeducationalmedia.com

The Human Body

Tab le of C ontents

T he human body is a strange and smelly thing of beauty . Made of seventy-ve trillion microscopic cells , our bodies can eat, drink, breathe, sleep, dream, grow , and heal. Not to mention poop and pee!

Skin Deep

About 95 perc ent of all the cells in the human body are bacteria. Most of these microbes are in the digestiv e tr act. Billions of bacteria also live on human skin!

Yo u Are (Mostly) Ba cteria

Bacter ia produce chemicals that help us use energ y and nutrients from food. Scientists think intestinal bacteria helps us maintain healthy immune systems.

Tiny Helpers

S kin protects our squishy insides from the outside world. You re probably familiar with skin, but did you know that the skin that we seethe epidermisis made of dead skin cells?

Y our skin makes up about 15 percent of your body weight. And every 27 days, our bodies make a completely new layer of skin for us to show off. Where does the old layer go? It akes off and becomes household dust.

Almost all household dust is dead skin cells. Next time your e vacuuming, remember t hat your e vacuuming up yourself!

Clean Y ourself Up

Like all mammals, our skin is hairy . The bulk of our hair is on our heads. Most people have about 100,000 individual hairs, and between 50 and 100 hairs fall out every day .

All hair is dead, except the hair still in your scalp s epidermis .

Dead Weight

H air is the second-fastest growing tissue in the human body . Only bone marr ow grows faster . Hair grows about ve inches (10.16 centimeters) a year . If you dream of sporting a head of oor -length hair , you better start growing it out now!

Hair contains information about substances that hav e been in a person s bloodstre am, including medications and drugs.

The Hair Knows

F ingernails and toenails also grow out of the skin. They are made of a tough, exible protein called keratin . Like hair and skin, our nails are mostly made of dead tissue. Nails are useful tools. They protect our ngertips from injuries and make our ngertips more sensitive. And in a pinch, they can open a can of soda, pop a balloon, or scratch a really good itch.

Some people like to grow their nails REALL Y long!

From sh to humans, almost every animal gets itchy. But why? Scientists recently discover ed specialized neurons that produce a chemical called Nppb . This chemical triggers the bodys itch re sponse.

It Itches!

The scientic wor d for an itch is pruritus . Accor ding to scientists , the r eason scr atching an itch makes it feel better is because scra tching causes pain! The pain overpowe rs the itchy feeling tempora rily. Researc h also shows that the cells and cir cuits that tr ansmit pain and itch are s omewhat overlapped.

Did Y ou Know?

Blood contains white blood cells , r ed blood cells , and platelets .

C ut too far into the skin, and youll nd blood. Most of us have about four to six quarts (3.8 to 5.7 liters) of blood swirling beneath our skin. It makes up about 7 percent of a person s body weight.

Inside Out

B lood moves things such as oxygen and nutrients around our bodies. It also takes away unwanted waste products. Blood travels in a complex web of tubes called blood vessels. The body has more than 60,000 miles (96,561 kilometers) of blood vessels. That s enough to wrap around the entire planet twice!

B eneath our skinand a layer of fatare our muscles. They make the body move. We have hundreds and hundreds of connected muscles.

S ome muscles we can control, like the ones in our arms and legs and butts. (The butt muscle is called the gluteus maximus , in case you were wondering.) But other muscles move all by themselves, like the muscles in our hearts and those we use to swallow .

Y ou may hav e hear d the old saying, It takes more muscles to frown than it does to smile! Science hasnt proven th is. Some studies have shown it takes 10 to 12 muscles to smile, and six to 11 muscles to frown. But, since people tend to smile a lot, the smiling muscles ar e str onger . Frown ing takes more effort because those muscles ar e w eaker .

F eeling D own Is Har d W ork

T o preserve, grow , and energize our bodies, we need food and water . When you eat, the muscles in your esophagus tighten and relax in a wave-like manner , pushing the food down into your stomach. This is called peristalsis .

In ra re inst ances, our bodies can cra ve food that isnt actually food, such as hair , deter gent, ashes , or plastic . This condition is called pica .

Str ange Cr avings

Esophagus