under the microscope in your body

It is made up of trillions of microscopic parts called cells.. Journey around your body We are going to take a tour of the human body so you can discover the world of living things that

Sabrina Crewe

Consultant:

Professor Anne K Camper,

Montana State University

Under the Microscope

In Your

Body

Copyright © 2010 by Infobase Publishing

All rights reserved No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher For information contact:

In your body / Sabrina Crewe ; consultant, Professor Anne K Camper.

p cm (Under the microscope)

Includes index.

ISBN 978-1-60413-825-2 (hardcover)

ISBN 978-1-4381-3369-0 (e-book)

1 Microorganisms Juvenile literature 2 Bacteria Juvenile literature 3 Microscopy

Juvenile literature 4 Human body Juvenile literature 5 Microscopes Juvenile literature I Title QR57.C744 2010

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Illustrations by Stefan Chabluk

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Book printed and bound by Bang Printing, Brainerd, MN

Date printed: May 2010

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The World Inside You

Take a look in the mirror You are very familiar with what you see there—your hair, your eyes, and the shape of your body But you probably don’t spend much time thinking about the inside of your body Nor do you put your body under the microscope and look at it up close

If you did, you would find that your body is

a world of its own It is made up of trillions of

microscopic parts called cells

Microscopic life

The cells are just the beginning, however You may think you are the only thing living in your body, but you are not! An incredible number of

microscopic living things inhabit your body along with you

Organisms are living

things, and living things too small to see with the human eye are called

microorganisms These

include microanimals so

tiny that they go unnoticed

on your skin Even smaller are the microorganisms

we call microbes Microbes include

bacteria, protists, microfungi,

and viruses We’ll find out about

all these things in this book

Journey around

your body

We are going to take a tour

of the human body so you can

discover the world of living things

that make their homes inside you

Before we do that, let’s take a look at

the cells you are made of and find out

how they make you what you are

Micro-Fact

You are made of about 100 trillion cells And for every single one

of those cells, there are ten microbes in your body!

When things are magnified, you see them in a different way This is part of an iris, the colored part of a human eye The blue pool at the bottom is the pupil, which

is the black circle in the center of your eye that is actually

a hole

cell membrane

nucleus cytoplasm

Cells are the units that all living things are made of

We’ll be seeing a lot of cells as we travel around the microworld of your body That’s because all parts

of you—from your hair to your toes—

are a mass of microscopic cells

Cell structure

Whether a cell is in a strand

of your hair or part of a toe

muscle, it has the same

basic structure You can

see the basic cell parts

in this diagram

The organelles

of this human cell

include the nucleus,

which controls the cell The ribosomes produce protein, which cells are made of The mitochondria process oxygen and food to make energy for their cell

The membrane holds the

cell together and protects it

It is filled with a substance

called cytoplasm, which

contains various smaller

parts, or organelles Each

type of organelle has a

particular job to do to keep

the cell working properly

The headquarters of the

cell is called the nucleus

You’ll find out more about

the nucleus soon

Life of a cell

Things are always changing in your body Every second, some cells are dying and others are being made Where

do the new ones come from? Many cells reproduce

themselves simply by dividing First the nucleus splits

in two Then the cell stretches in the middle and splits,

with each nucleus becoming the center of a new cell

Micro-Fact

Some human cells

live for just a day,

while others last

for years

These are nerve cells, or neurons— the type of cells that make up the nervous system The nervous system carries messages around the body Messages travel through strands that connect neurons

to each other and to other parts of the body, such as muscles.

A Look at DNA

and Genes

So how does a cell in your tongue know to look and act like

a tongue cell? Why doesn’t it become a piece of knee or stomach? The answer lies inside the nucleus of every cell Let’s take a look under the microscope

Nucleus in control

We read earlier that the nucleus controls the cell What does that actually mean? It means the nucleus directs the functions

of the other organelles But the nucleus also contains instructions—a type of recipe—that the cell follows when it develops It’s how the cell “knows” what to be

Chromosomes and DNA

The packages in the nucleus that hold this vital information are

called chromosomes

These are tightly coiled

strings of molecules of

These are human

chromosomes like the

ones inside all the cell

nuclei in your body They have

been magnified about 10,000

times Your cells contain two sets of

chromosomes, half of them from

your father and half from your

mother The chromosomes

carry DNA arranged in the

patterns that form your

own special genes.

The way the

strings of DNA are

arranged is the key

to making a cell what

it is In fact, DNA makes

you who you are Stretches

of DNA molecules form patterns

called genes Each gene, or pattern,

holds the information every cell needs

to develop and function When new

cells form from existing cells, the

information is passed to the new

cell because the chromosomes

6 centimeters) long That may not sound very long But the string is packed into a chromosome only

1 micrometer wide, and

1 centimeter is 10,000 micrometers!

Genes are

passed from

parents to children

Because they have

similar gene patterns,

people in the same

family often

look alike.

Bacteria in the Body

We already read that there

are different kinds of

microorganisms that live

in and on your body:

microfungi, tiny animals,

and even tinier bacteria

and viruses Let’s learn

about bacteria, because

we’re going to find them

everywhere!

What is a

bacterium?

A bacterium is a living

thing, like an animal But

there are several important

differences Bacteria have

only one cell, and it is

simpler than the human

one we looked at earlier

Unlike plants and animals,

bacteria reproduce by

simply dividing in two!

Bacteria that live in or

on people absorb food from

whatever part of the body they

call home This could be the oil on

your skin or the food in your stomach

Escherichia coli

(E coli for short) is a

bacterium that lives in people’s intestines It is usually a good bacterium,

but some kinds of E coli cause

food poisoning You can see that the bacterium in the center is dividing, and it will soon separate into two cells These bacteria have been magnified about 26,000 times.

Good bacteria

Bacteria can be very useful as they

process their food—in fact, we

couldn’t live without them Out in

the world, they digest waste, such

as dead plants, and turn it into

nutrients Inside your body, many

bacteria help digest your food

Groups of bacteria inside your

body and on your skin also help

fight off germs

Bad bacteria

Some bacteria that live on our

bodies are harmful, however

Microbes that make us sick

are what we call germs,

but scientists call them

pathogens Several common

pathogens are bacteria that

find their way into or onto

our bodies They may enter

in the food or water we

consume, or they may

be in our environment

Pathogens release

chemicals that harm

us instead of help us

These chemicals, or

toxins, can destroy cells

or cause food poisoning

Micro-Fact

Some bacteria can divide and multiply several times injust one hour

This image shows several kinds of bacteria, most of which live on our skin Many bacteria are shaped like a straight rod, while some are twisted Others are ball-shaped

Some have flagella (little tails

that help them move around) You can see that some of the bacteria in this picture are dividing to reproduce

themselves.

A Layer of Skin

It would be impossible for our bodies to exist without the layer of skin that covers us Skin keeps our insides

in and protects them from the outside world It is a barrier against hot and cold weather, water, and the knocks and bumps of daily life

Defense and attack

Skin is also the first defense your body has against pathogens that attack you, such as bad

bacteria Sweat contains chemicals that help fight off pathogens Our skin is home to about 1,000 different

Micro-Fact

Every square inch of

skin contains 30 million

cells Between 10,000 and

1 million microbes live

on each of those

square inches

Staphylococcus epidermidis bacteria

live on human skin They cluster together in colonies like the ones you

see here Staphylococci

measure about

1 micrometer across These have been

When you see fungi growing outside, they look like plants—mushrooms are a fungi, for example But fungi are different from plants They spread

threads called hyphae across

the food source they live on Fungi with microscopic hyphae are called microfungi Some microfungi, like this one, live on human skin This fungus causes athlete’s foot You can see the hyphae (orange) spreading among the flakes of skin

types of bacteria Most

are harmless, and

some help protect our

bodies The bacterium

Staphylococcus

epidermidis, for

example, lives all

over the body It can

protect us from a

similar bacterium,

Staphylococcus aureus,

which causes skin

infections and other

diseases

Animals on

your skin

There are several

microanimals that can

live on you or feed on

your skin These include

several types of mites

The female scabies mite

actually digs into the

skin to make tunnels!

She lays her eggs as she

goes, and these eggs

soon hatch to produce

more mites Scabies

mites cause a rash and

terrible itching

Lice hold on

tight by wrapping

their claws around

your hair You can see

that this louse has

already attached an

egg to the hair.

Life on Your Head

You probably know about lice, even though you may not have seen one Lice are very small insects that like to live in our hair

Dribbling lice

People with lice infestations have very itchy

scalps The itch is caused by dribbling lice! To get food, lice puncture the skin of the scalp with their mouthparts and suck out blood As they feed, lice drool liquid, which is like

the saliva in your mouth This louse

dribble irritates most people’s

skin and makes them itch

Almost everyone has eyelash mites living in the hair follicles (tiny holes) from which their eyelashes grow The mites feed

on skin oils and the dead skin around our eyes This picture shows the tails of eyelash mites sticking out of a follicle next

to an eyelash (right) In real life, eyelash mites are 0.25 millimeters long These have been magnified 139 times

Sticky nits

Females lay eggs,

called nits, once a day

They make sure the

nits stick to a person’s

hair by covering them

with glue The eggs

look like tiny white

specks, and they are

just visible if you

look carefully After

about a week, the

nits hatch, and out

come new lice

Catching and

killing lice

It’s easy to pick up

lice from other kids

at school if you have

your heads close

together The lice

simply crawl from

one head to another

There are special

shampoos that can

kill lice You need to

use a fine-tooth

comb to dislodge

the sticky nits

Inside Your Mouth

Lots of stuff gets into your body through your mouth, and a lot goes on there It’s quite a center of microscopic activity!

Your tongue

It’s fun to take a close-up look at your tongue It looks pretty smooth until you put it under the microscope Then you see that your tongue is covered

in small lumps called papillae Some contain rounded taste buds, which you use to taste your food Other papillae are spiky and help hold onto food and move it around The papillae also let you know if your food is too hot or too cold

Germ Barriers

Your mouth has

cells that are tightly

packed together,

which makes it hard

for the pathogens

Biofilm on Your Teeth

Teeth are covered in hard material called enamel, which is made of calcium and other minerals Enamel is tough so you can bite and chew food without breaking your teeth You’ve probably heard plenty of times how important it is to keep your teeth clean If you don’t, they get covered in plaque and start to decay Under the microscope, we discover that

plaque is actually a slimy substance, called biofilm, with

bacteria in it Some of the bacteria produce this slime to help them stick to your teeth Some biofilm is a good thing—

it protects your teeth from pathogens But if you let too much plaque build up on your teeth, the bacteria will eat away

at the enamel and cause your teeth to decay

Into the Bloodstream

We’re going to take a look at the amazing system called the bloodstream It is

a transportation network running through your body, carrying blood to every part of you

What is blood made of?

The liquid part

of blood, called plasma, is mostly water, but it also contains nutrients The main job of plasma is to transport three types

of blood cells: platelets, red blood cells, and white blood cells

Platelets are useful when you bleed They thicken up, or clot, at the wound and stop the bleeding That’s how scabs form over cuts

White blood cells are the body’s defenders against infection and sickness We’ll learn more in a while about how they defend your body

You can see

red blood cells and

white blood cells

traveling through

this blood vessel

in the liver The

blood is carrying

nutrients and

oxygen.

How Small

Is Small?

A red blood cell measures

about 7 micrometers across

A drop of blood 1 cubic

millimeter in size can hold

about 5 million red

blood cells

Red blood cells

Most of your blood cells are

red blood cells, and they give

your blood its color Their job is

to deliver oxygen and remove

waste When blood travels to

the lungs, red blood cells pick

up oxygen from the air you

inhale They travel around the

bloodstream, releasing oxygen

to all the cells that need it

Red blood cells also pick up

waste from the cells in the form

of carbon dioxide They carry

the carbon dioxide back to the

lungs, where you breathe it out

and get rid of it

Protozoa

Sometimes, microbes get into our blood They may belong to a group of

organisms called protozoa,

which are animal-like protists Most protozoa catch or find food, but a few

are parasites, which means

they absorb food from a host If that host is you, the protozoa are likely to make you sick Sleeping sickness, dysentery, and malaria are all illnesses caused

by parasitic protozoa The protozoa below, in amongst red blood cells, are called trypanosomes, and they cause sleeping sickness The green threads

are their flagella