6

The stucture of the body

Can you imagine the number of grains of sand it took to make this magnificentwork? A little like this sculpture on thebeach of Hardelot in France, our body is composed of billions of bits ofmaterial—tiny structures called cells. Unlike grains of sand, however, cells are

living things: they are born, they eat, they grow, they reproduce, and they die.The human body contains more than 50,000 billion of these little microscopicmarvels! Before we go any further, allow me to present them to you…

Dear brother,

It was delightful having you visit me at Neufch�tel. What

an extraordinary vacation we had together. I wish you the

very best of luck with your scrapbook on the human body,

which you told me so much about. As promised, I�m sending

you photos of our excursion to the sand sculptures.

Love and kisses

from your sister

CYTOPLASM is a jellylike substance

in which the organelles float.

Organelles are the tiny components of

the cell. Most cellular activity takes

place in the cytoplasm.

The CELLULAR MEMBRANE

surrounds the

cytoplasm. It ac

ts as

security guard

for the cell, co

ntrolling

whatever enters

or leaves it.

The ENDOPLASMIC

RETICULUM is

a set of membranes that

form canals. It produces

proteins and digests all

kinds of chemical substances.

The MITOCHONDRIA

produce and store the

energy needed for the cell

to function properly.

The NUCLEUS is the control

center of the cell. It directs

all activities and also contains

genetic material (we will talk

about this mysterious

material later).

The RIBOSOMES can join

with the endoplasmic reticulum to

manufacture proteins.

Certain vesicules, called VACUOLES,

transport the proteins to the cell’s

membrane where they are released.

The cells in your body are like miniature factoriesthat all contain more or less the same basic

equipment. Here they are:

The GOLGI APPARATUS

“packages” the proteins for

transportation out of the cell.

(There are thousands of proteins,

which are chemical substances.

Each protein has a specific task.

Some may work to help

muscles contract, for example,

or may carry oxygen.)

Cells are not all identical. Their shape and size varyaccording to the role theyplay inside thebody. Hereare someof them:

7

Cells do not function all by themselves. On the contrary, they are trueteam workers. Similar types of CELLS get together to createTISSUES designed for specific tasks. To perform even more complextasks, different types of tissue may be combined to create ORGANS.

Finally, several organs may be combined to form a SYSTEM.In the digestive system, for example, several organs, likethe stomach and the intestines, work together to ensurethat food is digested properly. Picture these systems likethe players on a baseball team, whose members rely onone another, each performing a function that contributes to the success of the entire team.

Hooke’s microscope

Neuron

(nerve cell)

Rod (cell in the retina of the eye)

Erythrocyte

(red blood cell)

DISCOVERY OF THE CELL

In the 17th century, English scientist Robert Hooke, using a primitive

microscope, discovered box like compartments in the stems of certain plants.

He called these compartments “cells,” in reference to the rows of small

chambers occupied by the monks in monasteries. In 1839, more than

150 years later, two German scientists, Matthias Jakob Schleiden and

Theodor Schwann confirmed that all living beings are composed of cells.

Inventors and Inventions, p. 122

MICROBIOLOGY (from the Greek words

mikrobios [small life] and logos [to study]).

The science that is concerned with microorganisms;

the study of microscopic life.

Straight from the body VOL. 3, NO. 9 September 2003

Home Editorial Columns Articles Archives Info

The birth of cellsEvery minute, about 300 million cells in the body die, but nearly all are replaced. Luckily, most cells areable to reproduce, forming a completely new cell. The complex process resulting in the creation of a newcell is called mitosis, or cell division.

In 1590, a Dutch eyeglass maker called Hans Jansen and his son Zacharias invented the first microscope. With this device they were able to look at things too small for the naked eye to see. Thanks to their genius, a new microscopic universe suddenly opened up to the scientists of that time. Englishman Robert Hooke was one of the first scientiststo explore this unknown world. Take a look at this excerpt from an encyclopedia that I’ve pasted below.

8

Whether it is pale or dark, smooth orwrinkled, soft or rough, the skin is oneof our most precious organs. Like agiant envelope covering the body, theskin is a marvelous natural barrier. It protects us from the Sun’s burningrays, heat, cold, and the shock ofimpacts. It also prevents germs fromentering the body. Did you know thatthe skin even plays a role in nutrition?It produces vitamin D, which helps thebody absorb the calcium it needs forgrowth and healthy bones. Last butnot least, the skin is the organ for oursense of touch. There is so much tosay about the sense of touch that I’ve decided to devote two entirepages to the subject a little later on in my scrapbook.

The cells of the

DERMIS produce a

combination of strong

fibers and flexible ones.

These fibers prevent the

skin from tearing and

give it suppleness.

The FAT conserves body heat and

cushions the shock of impacts.

The SWEAT GLAND

secretes sweat.

The PORE carries sweat

to the surface of the skin.

The heaviest organ

The skin is the body’s heaviest organ.

The average adult’s skin weighs

between 9 and 15 lbs (4 to 7 kg).

MY RECORDS OF THE HUMAN BODY

The EPIDERMIS

is the surface of the

skin, the part that

we touch.

The thickness of skinvaries from 0.02 in. (0.5 mm) for an eyelidto more than 0.2 in. (5 mm) for the sole ofa foot. The skin is madeup of two principallayers: the epidermis and the dermis. Here isan illustration showingyou the most important parts of the skin.

Special RECEPTORS detect changes

taking place around the body, for example, in

pressure and temperature. I will talk more

about these receptors on pages 22 and 23,

when the subject of touch comes up.

Take a good look at your fingers andthe palms of your hands. The patternsof fine lines traced on your fingertipsare your fingerprints. It is believed thatthese tiny furrows help give the handsa better grip on objects, a little like theway treads on running shoes keep youfrom slipping on a waxed floor. Eachperson’s fingerprints are unique; thereare no others exactly like them in theworld. By comparing the fingerprintsfound at a crime scene with those ofknown criminals, police can quickly identifythe guilty and eliminate the innocent.

The BASAL cell layer

is situated at the base

of the epidermis.

The skin: a living barrier

The SEBACEOUS

GLAND secretes a

natural oil called sebum,

which helps prevent the

skin from drying out.

MUSCLE

makes the hairs on

the skin stand up

when it is cold. This

phenomenon is known

as “goose bumps.”

The cells of the HAIR

FOLLICLES manufacture

hair. The color of the hair is

determined by a combination

of yellow, brown, and black

melanin pigments.

The BLOOD VESSELS carry blood to the cells of the skin and back from them.

A natural thermostat

The body must maintain a steady temperature of

98.6°F (37°C) to work effectively. At the first sign of

overheating, millions of tiny glands in the skin begin

to secrete sweat. As the sweat evaporates, or dries,

it carries off excess heat and helps the body feel

refreshed. Under conditions of intense heat or physical

effort, humans can perspire almost 3 gallons (11 liters)

of water a day.

Even odorless perspiration can acquire an unpleasant smell. This happens when bacteria, microorganisms that live on the skin’s surface, destroy some of the substances they contain. Did you know that a man can accumulate more

than 13 million bacteria per square inch (6.45 cm2) under each armpit?

Artificial skin!

International Press Agency, March 8, 1999 — With most

cuts or scratches, the skin is able to repair itself

quickly, but it is not the same for serious wounds.

In the case of deep burns, for instance, the skin is

not able to manufacture new cells quickly

enough. The good news is that doctors are now

able to use artificial skin, made in the laboratory.

This skin, which comes in transparent strips,

appears to be a promising invention!

Unbelievable but true!by Itza Mazing

Scientifically Yours, January 2004

Melanin pigment is a colored substancethat gives skin its color. The more theskin is exposed to the Sun’s rays, themore pigment is produced and theskin becomes darker. This process isknown as “suntanning.” Pigments areimportant; they shield the skin andprotect its cells from harmful ultraviolet(UV) rays. Melanin comes in a range ofcolors that runs from yellow to brownto black. The type and

amount of melanin in the skin varies from person to person, which

explains why your skin is not exactly thesame shade as your brother’s or sister’sskin. Variations in melanin are also to befound among the different peoples of theworld. Melanin is like a paintbrush thatcolors every face its own unique shade.

9

Do you know that the dust that accumulates around thehouse is mainly composed of bits of dead skin? Everyyear your body loses from 6 to 8.5 lbs (3 to 4 kg) of oldskin. How is this possible? Simple! The skin’s basal cellsare constantly multiplying. Newly created cells “push” onthe older generation of cells, making them travel towardthe surface of the skin. The older skin cells rise graduallyin the epidermis until they reach the surface, where theydetach and fall off. In this way, we get to have acompletely new epidermis every 35 to 45 days!

Pounds and pounds of dead cells

SPONGY BONE resembles

a sponge.

SCIENCE

Bone is three times stronger than:

a) a cast iron bar of equal weight b) a wooden plank of equal weightc) a plastic tube of equal weight

THE DISCOVERY OF X RAYSA German physicist named Wilhelm Röntgen discovered X rays in1895. Although X rays are invisible, they are able to penetrate the humanbody and form an image of what lies inside on a photographic plate.While X rays can easily pass through soft organs like skin and muscles,it is more difficult for them to pass through denser material like bone.This results in white outlines on the photograph in place of bones.Within a few months of Röntgen’s discovery, many doctors were usingthe mysterious X rays to diagnose bone fractures. In 1901, Röntgen wasawarded the Nobel prize for his discovery.

Inventors and Inventions, p. 177

a) a steel bar

COMPACT BONE is the

smooth, dense substance that

covers the outside of the bone.

The MARROW in certain bones produces millions of

blood cells each day. These blood cells leave the

marrow through the blood vessels. (We will talk

about this again on page 32.) 10

Our bones are made up of cells, minerals, and proteins. The outer layer of bones consists of a hard material calledcompact bone. After tooth enamel, compact bone is thehardest material in the body. If we look inside a bone likethe femur, however, we discover that the center is made ofa lighter material called spongy bone (if you want to knowwhere the femur is located, take a look at my skeleton). If all our bones were made entirely of compact bone, ourbodies would be a lot heavier than they are! Here is adiagram showing the principal parts of a bone.

The BL

OOD V

ESSELS

carry

bloo

d to th

e bo

ne cells

.

Bones: the framework of the body

A friend of mine who is an etymologist (he studies theorigins of words) told me the word “skeleton” comesfrom Greek and means “dried-up body.” This ancientdefinition may be quite appropriate for skeletonsexhibited in museums, but it doesn’t at all apply tobones that are alive! Without bones, our bodieswould be mushy and would collapse. The skeleton ismuch more than a piece of scaffolding. Its bonesalso support the organs and protect them. The bones of the skull form a kind of “hard hat”around the brain, while the rib cage shelters the heartand the lungs. With the help of the muscles, many ofour bones enable us to move about. And if that’s notenough, our bones even have the job of storing fats and minerals our bodies need, and of producing blood cells, too!

The SKULL is made

of 22 bones.

Mandible (lower jawbone)

Clavicle (collarbone)

Scapula (shoulder blade)

Sternum (breastbone)

Rib

The body of an adult contains 206 bones of many different shapes and sizes. I’m sureyou can understand that I am not able toshow every bone in the human body onthis page, so I will just identify the mostimportant ones.

Vertebra

Coccyx

The VERTEBRAL COLUMN

consists of 33 vertebrae.

The HAND,

including the

wrist, has 27 bones.

Ulna

Radius

Humerus

Ilium (pelvis)

Femur (thighbone)

Tibia (shinbone)

Fibula (leg bone)

There are three main types of bones:flat bones, short bones, and long bones.The flat bones, like the ones in theskull, are thin and flattened out and are there to protect the organs. Theshort bones, like the ones in the wristsand ankles, are there to connect other

bones and help make joints flexible.Finally, the long bones, such as thefemur and the humerus, are used tolever the body. Located in the armsand legs, these bones allow us to makelarge movements.

The types of bones

A Guide to the Human Body, p. 26

Broken bone will healitself. At the moment abone is fractured, bloodruns out from the torn

blood vessels and forms aclot. Special bone cells then move

into the area of the injury and make afibrous plug called a callous. Gradually, the

callous replaces the blood clot and connects the two brokenends of bone. Over time the callous is transformed into actual bone

tissue. For a fracture to heal, a doctor often puts on a cast to keep thebone from moving while it mends. It takes about two months for the boneto repair itself and for everything to return to normal.

Long bone

11

Here is a science riddle.

Dear Professor,I had a really nasty fall off a horse and now myarm is broken. What is going to happen to me?

Emma

Short boneFlat bone

The FOOT is

made up of 26 bones.

The RIB CAGE is made up of the

sternum (breastbone) and 12 pairs of

ribs along with their vetebrae.

In an average person, the ligaments limit the movements of thebones. Contortionists, on the other hand, have ligaments that areparticularly flexible, allowing them to perform highly unusualmovements! This extraordinary elasticity in the ligamentscan be found mainly in young girls and seems to getpassed on from one generation to the next.

A flexible body

As we learned on the previous page, our skeleton is a real masterpiece ofconstruction! Apart from supporting our body and protecting our organs,our bones also make it possible for us to move about. In fact, it isbecause of the joints that connect bones, along with some powerfulmuscles, that we are able to perform many kinds of complex movements.As you read this, try scratching your nose with your hand without

bending your elbow. It is the joints connecting the different bones thatmake the skeleton flexible. The joints of the vertebrae, for example, allowlimited movement, while those in the shoulders provide greater flexibility

and allow movement in many directions.

Although our joints are very mobile, the bones in them do notmove about freely. They are held firmly in place by ligaments,

which are bands of tissue that are both solid and elastic.The ligaments allow movement in certain directions whilekeeping the bones firmly attached to each other. On theleft, I’ve illustrated the different parts of the knee joint.

Muscle

Femur (thighbone)

LIGAMENTS

hold the bones together.

CARTILAGE is very smooth.

Besides cushioning against impacts, it

allows the bones to move without

rubbing against each other.

Tibia (shinbone)

The PATELLA (kneecap)

is a rounded bone

that works like a lever.

12

Even though our joints haveremarkable flexibility, theirrange of movement is notunlimited. Have you everinjured your ligaments byspraining an ankle, forexample? Sprains as well as torn ligamentsare quite commonamong athletes.

The SYNOVIAL FLUID

lubricates the joint, reducing

friction on bones. It prevents

the joints from wearing out.

TENDONS

attach the muscles to the

bones at the joints.

CIRCUSStars

of

The jugglers, clowns, and acrobats are back in town

Be sure not tomiss the newest act by internationally renowned contortionist Ella Stick

See over for details

13

There are several different kinds of joints. They are groupedaccording to their structure and the kind of movement they perform.Did you know that joints have even been the inspiration for many ofthe mechanisms designed to move the objects that surround us? Here are a few examples:

The largest jointThe knee joint is the largest joint in thebody. It can absorb a force equivalent to seven times the weight of the body. It is very vulnerable to blows from theside, however, and is the joint that is most often injured.

MY RECORDS OF THE HUMAN BODY

Pivot jointThe pivot joint allows us to turn ourhead or twist our forearms.

Ball-and-socket joint

The ball-and-socket joint is only found

in the shoulders and the hips. It is the

joint that allows the greatest freedom

of movement.

Hinge-type jointThe hinge-type joint, like that found in

the elbow or knee, allows us to perform

limited back-and-forth movements.

Plane-type jointThe plane-type joint allows two bonesto slide against each other, either backand forth or from side to side. It can befound at the base of the thumb.

Subject: Registration confirmation

Date: August 19, 2003

To: Professor Genius

Dear Professor Genius,

We would like to confirm your enrollment in our sign

language course scheduled for the Fall 2004 session.

In the meantime, we are sending you the first 10 let

ters

of the American alphabet. You will be required to me

morize

them in time for the first class, which will be held

on

September 15. Please do not hesitate to contact us for

more information.

M. Largehand

Staff Professor, World Languages School

The hand alone has 19 joints! This marvel of engineering allows us

to perform very precise tasks likewriting, embroidering… even communicating!

I am really enthusiastic about starting thissign language course. You will probablyhear more about it from me later.

A

B

C

DE

FG

H

I

J

C

I

J