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your body.

Your skin regulates your body temperature as it is rich in blood supply.

Your skin can alter the blood circulation by dilating (relaxed) and

constricting (narrowed) the blood vessels. This regulates your body


If you have a fever, blood vessels in the skin dilate and heat escapes from

your body. At the same time, more sweat is produced which helps to cool the


Skin has melanin, a black pigment which absorbs harmful rays from the sun.

So, you need to take care of your skin by:

Keep it clean with regular bathing.

Use good sun protection methods like carrying umbrellas while you are

in the sun and applying moisturizers to keep it smooth.

Why is clipping our nails painless though it is

growing tissue?

Clipping nails is painless because there are no nerve endings in our nails.

Most people clip their

finger and toe nails

about every week.

Would you do it if it was


Nail structure.


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A nail has two parts; the nail plate and the nail bed.

A nail plate is the hard plate that we clip. It has no nerve endings, so it's not

painful to clip it.

The nail bed is the soft part below the nail plate. The nail plate is attached to

the nail bed. It has a germinal matrix at the back of it, from which the nail


In contrast to the nail plate, the nail bed is rich in nerve endings. So, any pin

prick or damage to the nail bed is very painful!

So, be careful not to contact the nail bed when you clip your nails.

Why are boils dangerous in the central area of the


The central area of the face around the nose is called the 'danger zone of the

face'. You shouldn't squeeze the boils or pimples there.

The danger zone of the face is a triangular area from

the bridge of the nose on both sides with the upper

lip as a base.

The veins of the face are connected to the big venous

pool of blood inside the skull called ' Cavernous

sinus'. It can be very dangerous if an infection from

the skin passes to this venous sinus unless you get proper treatment as soon

as possible. So, avoid picking or squeezing the pimples or boils on the face.

Why do hot things burn the skin?

When you touch a hot object which is hotter than your body, the heat from

that object flows into your skin. The skin has cells in it. These cells contain

many molecules. At body temperature, these molecules are in continuous


When heat flows through the cells, these cell molecules move much faster.

This fast movement damages the cells and nerve endings at that local area.

This sensation is felt like 'burning' by our brain.

Why does burnt skin become white?

If heat is applied a little longer, the cells in the area become damaged and


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dry up. This causes the white and charred appearance. Blood circulation

increases to the burnt area, so the surrounding area looks reddish.

Why do we get “goose bumps”?

Have you felt small bumps on your skin when you go out in cold weather or

feel scared while watching a scary movie? They are called 'goose bumps'

because the fine bumps resemble the skin of a goose after the feathers are


Piloerector muscle that causes goose bumps.

We get them because of a tiny muscle, called the 'erector pili', which is

attached to the follicles of the hairs on our skin.

This tiny muscle contracts in response to cold or fright response making the

hair stand up on the skin.

When we feel cold or frightened, the impulses go to the brain through

sensory nerves. Then, the brain sends signals to the appropriate muscles and

the erector pili muscle, making it contract. The process where the hair stands

up on the skin is called 'piloerection'.


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This lasts for only a few seconds. If you gently rub your goose bumps and

make them feel a little warmer, they will go away.

Why do our lips, palms and soles

get chapped in cold weather?

There are small glands called 'Sebaceous glands' in our skin. The glands are

attached to the hair follicles.

These glands produce an oily material called 'Sebum' which helps to keep our

skin smoother.

There are a lot of sebaceous glands on our scalp, neck, chest and other parts

of the body.

But, there are no sebaceous glands in the skin of our palms, soles or the

lower lip. So these are the first areas to dry out in cold weather.


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Hygiene and Related Topics

Why should we wash our hands with soap before


There are millions of germs on the surface of our skin. Our hands touch many

surfaces while we do our routine work and germs are transferred on to our


If we eat without first washing our hands properly, these germs will cause

many diseases like gastroenteritis, fevers etc.

Simply washing just with water is not enough. You have to wash your hands

properly with soap to lift the dirt and grease from our hands and make them


The soap is acting as a 'surfactant', lowering the surface tension of the water.

Did you know that our body has a surfactant too? It is called the 'pulmonary

surfactant' and is seen in the lungs. This pulmonary surfactant covers the

alveoli of the lungs where air exchange takes place. It prevents our lungs

from collapsing.

How are germs killed in our body?

Every minute we breath germs, swallow germs, hosts germs on our skin.

But, not all germs are harmful. The harmful germs can be stopped from

invading our body by many protective mechanisms like:

* Lining of the respiratory tract is covered with the mucus and the cilia to

trap germs.

* Saliva in the mouth stops growth of the bacteria and keeps the mouth


* Acid in the stomach kills many harmful germs.

If the germs get past the above barriers, there are other methods that kill

them and protect the body.

In the blood there are two types of cells called -




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Lymphocytes are classified as:


Helper T-lymphocytes

Killer T-lymphocytes


The left side of the image explains ‘humoral immunity’. Harmful antigens IN


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OUR BLOOD are dealt by this immunity.

The right side of the image explains ‘Cell mediated immunity’. Harmful

antigens INSIDE OUR CELLS are dealt by this immunity.

How do B-lymphocytes protect us? B-lymphocytes provide a type of

immunity called 'humoral immunity'. When germs (like bacteria) invade our

blood, B-lymphocytes recognize the protein molecules on the surface of the

bacteria as foreign material. We call these foreign proteins as 'antigens'. B-

lymphocytes produce 'antibodies' against the antigens. These antibodies bind

with the antigens on the bacterial surface like a coating. Macrophages engulf

the antibody-coated bacteria and kill them!

(Lysis means “destruction”).

How do T-lymphocytes protect us? T-lymphocytes provide a type of

immunity called 'cell-mediated immunity'. T-lymphocytes are very useful

against germs that are inside the cells. When our body cells are infected with

germs, 'helper T-lymphocytes' are activated by macrophages. These helper

T-lymphocytes produce some substances which activate 'Killer T-

lymphocytes'. Killer T-lymphocytes attack our body cells that are infected by

the germs and destroy the cells, so the infection doesn't spread to normal


Pretty cool ... huh? We have to be thankful to our immune system that

protects our body from many harmful germs.


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Skeleton and Related Topics

Can people get shorter in the evenings?

It may seem unbelievable, but it is true. People can become shorter by an

average of 6 to 20 mm in the evening.

Intervertebral disc: The jelly like

structure between vertebrae which

acts like a shock absorber.

Our back bone is called a spinal

column. It protects our spinal cord.

The spinal column is not a single

bone. It is made up of 'vertebrae'

(vertebra; singular). Each vertebra

is a ring-like bone. They are

arranged one above another and all

are separated by an 'intervertebral


This intervertebral disc is made up of a jelly like center with surrounding

tough fibrocartilage. The disc acts like a shock absorber and prevents the

vertebrae clashing with each other. The central jelly-like substance is made

up of water, proteinaceous components and collagen.

These intervertebral discs get compressed as we stand and walk. They go

back to normal while we lie down. This changing state of the discs causes the

height difference in a person. Each person may get up to 1% shorter.

Why are bone fractures more common in old people?

Falls and fractures are common in old people, especially hip fractures.

Bone density: As people get older, their bones lose some of their density

and strength, and tend to fracture more easily.

This is called 'osteoporosis'. The effects of osteoporosis may be reduced by

regular exercise, and eating a diet that is high in calcium and vitamin D from

an early age.

Bone collagen: Bone collagen also becomes more brittle and gets damaged


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more easily as we get older.

In many countries, accidental falls by elderly people may cause serious injury

or even death.

What is a collar bone?

The collar bone is a flat bone near the shoulder called the 'clavicle'. The word

clavicle comes from a Latin word 'Clavicula', which means 'little key' because

the clavicle rotates like a key when we move our arm away from our body.

The main function of the clavicle is to keep the arm away from the body so

that our arm

movements are not


You can feel your

clavicle by passing

your fingers from your

shoulder toward your

neck. It is just below

the skin. A child’s

clavicle can be easily

fractured as it is still

developing until we

are almost 25 years of age.

Why are our bones so strong?

Bones form our skeletal system which supports the softer parts of our body.

The compressional strength of a human bone is up to forty times greater

than concrete! Why are bones so strong?


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Bone and Osteon.

Bones contain a lot of

calcium as


crystals' and collagen.

Both make bones

strong. 99% of our

body's calcium is in our


Our bones are actually

made up from two

types of bone; compact

bone and spongy bone.

The compact bone is

made up of 'Haversian canals’, or ‘Osteons',

which are narrow channels containing blood

vessels. The collagen fibres in the osteons spiral

around the osteon axis giving more strength to

the compact bone.

The spongy bone is called that because of its

honeycomb appearance.

Bone (especially spongy bone) constantly

rearranges itself to a form which can best

support the stresses on it over a period of time. This continuous adaptation

makes it stronger for any particular stress or weight.

To keep your bones healthy, you need to drink milk every day, eat food

which is rich in Vitamin D and exercise regularly through sport, running and

other activities.

Why is the first vertebra called the 'Atlas'?

Bend your neck and put your fingers on the midline across the back of your

neck. Gently press with your fingers and move them slowly down.


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You will feel bony projections. This central bony column is called your

'vertebral column'. It protects the spinal cord and is made up of many


The top vertebra (singular) is called 'Atlas' because Atlas was a deity in

Greek mythology who held all the heavens above with his shoulders and

hands. The Atlas vertebra holds the weight of your head and all the valuable

parts inside it.

The Atlas vertebra doesn't have a body like other vertebrae. This makes it

easy for us to bend and nod our head.

A fracture of the Atlas is very dangerous because that can cause paralysis of

the body from the neck down.

What are Sesamoid bones?

The sesamoid bones are sesame-shaped bones in the muscle tendons near

your joints. They protect the tendons when the muscles are working and

reduce any friction during movements. They may look a bit different but they

are real bones.


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The patella is

the biggest

sesamoid bone

in the body.

There are many

sesamoid bones

in our body. Most

of them are

small; less than

an inch long.

The biggest

sesamoid bone in

your body is

called the

'patella' which is

in front of the

knee joint. It is a

little less than 2 inches wide and about one and a third inches long in an

adult person. The patella is also called the 'kneecap'. It helps to maintain

proper movement of your knee.

What might happen if we didn't have a skeleton in

our body?

If we didn't have our skeleton supporting us, we would be a loose mass of

cells or a mass of muscles.

Our skeletal system is divided into an 'axial skeleton' and an 'appendicular


The axial skeleton is the central skeleton (skull, vertebral column and rib


The appendicular skeleton is the peripheral skeleton (upper limbs, lower

limbs as well as our shoulders and pelvic bones).

Our skeletal system protects the organs within our body. For example, the rib


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cage protects our lungs and heart while our skull protects our brain.

Our muscles are attached to the bones of our skeleton. Muscle and bone

movement lets us move around and do things.

Our skeletal system supports the body positions we can use. If we stand, it is

the bones within our skeleton help us to remain upright.

Some long bones have bone marrow in them. This is where we produce red

blood cells and white cells that fight invading germs.

What does, “Muscles act as Agonists

and Antagonists to carry movements” mean?

We do a lot of different movements with our body like running, jumping,

sitting etc. For smooth co-ordinated movements, you have different muscles

which either work together or in opposition to each other.

A group of muscles that make a specific movement possible are called

‘agonists’. A group of muscles that oppose the movement carried by the

agonists are called ‘antagonists’.

When you bend your elbow, the 'triceps' muscle behind your upper arm acts

as an agonist by contracting (pulling), while the 'biceps' muscle in front of


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your upper arm acts as an antagonist by relaxing.

Why does a child have more bones in their body than

an adult?

Children have 300 bones in the body while an adult has only 206! We

humans have long bones in our bodies. Long bones are longer than they are

wide and they grow in their length. Some of the longest bones are in your

upper arm, lower arm, upper leg, lower legs and your hands and feet.

Each long bone has three parts:

1) Upper 'epiphysis'

2) Middle 'diaphysis'

3) Lower 'epiphysis'

Long bones have

two epiphyseal

ends with a center


In a newborn baby

or a small child,

the epiphysis at

each end is

separated from the

diaphysis in the

middle by growth


This makes it look

like they have

three separate

bones on X-rays,

so people makes

the count of bones in a small child higher than in an adult. The cartilage in

the two ends will change as the child grows and all three parts will fuse to be

a single bone.


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In the picture above, which is a diagram of a long bone called the 'tibia', you

can see three separate areas in the child’s bone. These look like three bones.

By the time the child becomes an adult, all three bones fuse together to form

a strong single bone and the bone count slowly comes down to the usual

adult number.

What is the smallest bone in the body?

Your middle ear has three small bones called ossicles.

1. Stapes (stirrup)

2. Incus (Anvil)

3. Malleus (Hammer)

The Stapes is the smallest bone in the body.

Size: 3.5 mm height, 3 mm long and 1.4 mm wide

Weight: 3 - 4 mgs

Shape: Stirrup shaped.

The Malleus is the bone attached to the ear drum on one side and the Incus

on the other side.


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The Incus, in turn, articulates with the Stapes.

The other side of the Stapes is attached to the round window of the inner


When sound waves vibrate the ear drum (tympanic membrane), the malleus

vibrates first.

These vibrations are transmitted through the three ear ossicles. From there,

the vibrations are carried to the inner ear fluid and cochlea. From here the

signals go to the auditory center of the brain for further interpretation of the



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Internal Organs and Related Topics

What is 'The Master gland' in the human body?

The pituitary gland is a small endocrine (meaning that it secretes hormones

that are carried through the blood stream and act on distant organs) gland at

the base of the brain. It is about the size of a garden pea (approximately 1.5

cm) and weighs about 1 gram.

This tiny gland controls many other endocrine glands in the body, so it is

called the 'master regulator' of the endocrine system.

The pituitary gland affects the following functions in the body:

Growth of the body

Milk production in females

Sexual function in both males and females

Blood pressure regulation

Body metabolism

If the pituitary gland is not functioning or over-producing its s cret


ion, it can

have serious effects which require prompt medical treatment.

Why is our urine sometimes yellow?

The color of our urine depends on how much water we drink and the type of


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the food we eat. Yellow urine is produced when we drink little water on hot

and sunny days.

Our kidneys have a major role in removing the nitrogenous waste products

from metabolism via the urine. Kidneys have many glomeruli, which are the

basic working structures that filter blood and form urine.

If you don't drink enough water, especially in a hot climate, the water

content in your blood will be decreased. The hypothalamus (a part of the

brain) detects this low blood water level and sends signals to the pituitary


The pituitary gland releases a hormone called the 'antidiuretic hormone’

(ADH). This hormone acts on the glomerulus (a ball of capillary blood

vessels) and tells it to absorb water because there is not enough water in the


So, the kidneys absorb more water, and concentrated yellow urine is


If you drink enough water (most doctors recommend a minimum of 8 glasses

spread through your day), then the urine color will probably be colorless or

pale yellow.

Other foods and vitamins we consume can also color our urine when they are

eliminated from our bodies.

How does a doctor measure your heart rate?

Put your left hand flat on the table with

the palm facing up. Put the index and

middle finger of your right hand on the

outside of your arm just above the

wrist. Press gently ... Can you feel a

steady throbbing?

These ‘pulsations’ are from the radial

artery. When the heart pumps blood,

the artery gives you one pulsation. So,

the number of pulsations in a particular time period are equal to the number


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of heart beats. This is called the 'heart rate'.

The heart rate can vary from 60 to 120 in a healthy person based on their

activity level, emotions, body temperature etc., but the usual rate is about

70 beats per minute, which means your heart is beating at 70 times per

minute to pump blood through the body.

How and why does your doctor listen to our heart


When you go to your doctor's

office, your doctor uses a

stethoscope to listen to your

heartbeats. Ask your doctor if he

or she can put the ear-pieces in

your ears while they keep the flat

plate chest piece of the

stethoscope on your chest so

that you can hear the sounds

which your own heart makes?

You will hear the alternate

sounds which are something like

lub and dub.

Did you know that doctors figure out many heart diseases by listening to

these heart sounds? What causes these sounds?


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The black vertical bars indicate heart sounds. The first heart sound is after

the atrial systole, where the myocardium in the left and right atria

(chambers) contract. This causes more blood to flow into the respective


The second heart sound is after the ventricular systole by which blood

pumps into major arteries to our body.

You should also look at the picture in the question, 'What is an odd artery

and odd vein in the body?' That picture will show you more about the

circulatory path of your blood.

There are four valves in the heart; two between the two atria and the two

ventricles, and two between the two ventricles and the pulmonary artery and

the aorta.

1. The tricuspid valve is on the right side of the heart between the right

atrium and right ventricle

2. The bicuspid valve is between the left atrium and left ventricle

3. The pulmonary semilunar valve is between the right ventricle and

pulmonary artery

4. The aortic semilunar valve is between the left ventricle and aorta.

Lub sound: When blood is collected into the right atrium (from the body)


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and the left atrium (from your lungs), they contract to push the blood into

the respective ventricles. Now, the ventricles start contracting to push blood

into the pulmonary artery and aorta. The tricuspid and bicuspid valves both

close to stop the blood going back into the atria. This produces the ' lub'


Dub sound: After the right ventricle pumps blood into the pulmonary artery and the left ventricle pumps blood into the aorta, they start to relax and start

to widen (the first stage of diastole) so they will be ready to receive more

blood. To stop the blood from going back into the ventricles from both

arteries, the two semilunar valves close, which produces the ' dub' sound. So, these sounds are produced by alternate closing of valves between atria and

ventricles and semilunar valves.

Are there millions of germs in our intestines?

Yes. Our small and large intestines are home for millions of germs. But, don't

feel scared. About 80% of these germs are harmless to us and most are

helpful to us in many ways.

All these germs (bacteria) are called ' intestinal flora'. They help us to

digest certain types of food like complex carbohydrates.

Some also bind to the surface of our intestines to help prevent harmful

bacteria attaching themselves to and damaging the epithelium tissue which

covers and protects those surfaces.

The harmless intestinal flora can help our immune system to develop

resistance in the intestinal wall to harmful bacteria.

When a baby is born, its intestines are sterile. Later, babies slowly get their

own internal bacteria (gut flora) as they grow, especially when they are

weaned (change from their mother’s milk to other food types).

Antibiotics that we are prescribed for medical conditions such as fever may

also kill some helpful bacteria.

Your doctor will advise you about this.


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How are waste products removed from the body?

Our body removes waste products through three mechanisms:

1. Respiration: Each cell in our body uses oxygen and creates carbon

dioxide after absorbing it.

This carbon dioxide could be dangerous to our body if it remained in it,

because it could increase the acidity of our body fluids. That increased acidity

would affect other body functions.

2. Waste products from the intestines: These are excreted as feces.

One way to keep your stomach healthy is eating fresh green vegetables and

fruit. This will help you to avoid problems like constipation which can develop

into something more serious.

3. Kidneys: Protein is a part of our diet. After the body processes the

protein, the remainder is nitrogenous waste. Your body converts this waste

into 'urea' which your kidneys will remove.

Your body has other minor ways of removing waste, including our sweat

glands and our liver which also removes waste products which are produced

when old red blood cells break down.

Are stones actually formed in the body?

Yes, stones can be produced in our 'gallbladder' and our 'kidneys'.

The gallbladder is a small sac-like pouch under the liver. The gallbladder

stores bile that the liver produces. When we eat, this bile is released into the

duodenum (the first part of the small intestine) by an automatic mechanism

where it helps in the digestion of fat.

Stones in the gallbladder are more common in females, mostly those who are

overweight are fat and in their forties. Some gallstones are caused by genetic

factors and rapid weight reduction.

Gall stones contain cholesterol, bile pigments and calcium.

Kidney stones are more common in men than gallstones.

There are different types of kidney stones. They contain calcium, oxalate and



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Your doctor's advice and medical treatment is essential for both gallstones

and kidney stones.

Is the absorption surface of a small

Intestine as big as a Tennis court?

The length of our small intestine is about seventeen feet. But, the whole

absorptive surface of the average small intestine is big enough to cover the

area of a tennis court!

We need that much because food passes through the small intestine within

two to five hours, so it has to be digested and absorbed quickly.

First image: A cut section of the small intestine with deep mucosal folds,

called ‘plicae circulares’.

Second image: Mucosa thrown into villi (tiny folds that project from the

surface) to increase the surface area.

Third image: The cells on the villi show microvilli which help to further


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increase the total surface area.

What increases the surface area of the small intestine so much?

1. Folds on the mucosa: Mucosa folds on itself to form folds called 'plicae

circulares'. These folds are like incomplete circles on the wall.

2. Villi: These are finger like projections of the mucosa.

3. Microvilli: The epithelial cells on the mucosa throw it's membrane into tiny projections.

All these increase the absorptive surface of the small intestine enormously to

help the greatest amount of nutrients, water and vitamins to be absorbed

into the small intestine.

Can the acid in our stomach dissolve razorblades?

Our stomach produces an acid called hydrochloric acid ('Hcl'). This acid is

very strong and can corrode metals.

Our gastric acid pH is 1 while the pH of our blood is 7.4. This means that the

gastric juice is very acidic because of the high concentration of hydrochloric

acid in it.

Metal of any kind that is swallowed would always cause serious injury or even

death before the stomach acid could dissolve it, but a study done by

scientists indicates that razorblades would be melted down by stomach acid

by 63% in 24 hours. ( Li P. K.; Spittler C.; Taylor C. W.; Sponseller D.; Chung

R. S. ; Department of Surgery, Meridia Huron and Hillcrest Hospitals,

Cleveland, Ohio, Gastrointestinal endoscopy ISSN 0016-5107)


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So, how does our delicate

stomach protect itself from

such a dangerous acid?

The stomach lining is covered

with a mucus layer which

protects the stomach

epithelium from damage by the

hydrochloric acid. Also, the rich

blood flow in the stomach

removes any hydrochloric acid

that leaks through the mucus


Any damaged cells will be

quickly renewed as the

stomach’s whole epithelium is

replaced within one to three


What is an Appendix?

If you ever go to your doctor

with a pain in your belly and

fever, the doctor will put you on the bed and check your belly on the right

side. He checks your ‘Appendix’.

Your appendix is a worm-like sac that hangs from the side of the cecum (the

first part of the large intestine.)

The appendix (doctors also call it the vermiform appendix) is on the right

side of the belly below the navel. Doctors call that point "McBurney's Point".

They press gently on this point to see if you have pain there.

If you do, he will check your blood and belly to see if you have appendicitis.

This is an infection in your Appendix which will cause you to get fever, a pain

in your belly and to vomit.

In the picture, the appendix is the red worm-like extension on the


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large intestine.

If the doctor thinks it is

necessary to remove your

appendix, you will probably

wonder, 'What happens if I don't

have my precious appendix?'

Don't worry. Ask your family

and friends; one of them will

probably have had their

appendix removed. The

operation, called an

"appendectomy" is very


Is your friend or relative having

problems because their appendix was removed? That’s very unlikely.

Your appendix is a vestigial organ. This means that it is a rudimentary

organ that serves no purpose in humans. It is useful in some animals like

monkeys as part of their immune system. So, it is OK for humans to have

their appendix removed.


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