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101 Facts About the Human Body

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"101 Facts About the Human Body" by Radhika Venkata

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important subject. The author obtained the information from sources

believed to be reliable and from her own personal experience, but she neither

implies nor intends any guarantee of accuracy.

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reported in this book is only the author's personal opinion . You must do you

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The author, publisher and distributors never give legal, accounting, medical

or any other type of professional advice. The reader must always seek those

services from competent professionals that can review their own particular

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The author, publisher and distributors particularly disclaim any liability, loss,

or risk taken by individuals who directly or indirectly act on the information

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should any be assumed. The pictures are only licensed for use in this book

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Some Images © 2009 Jupiter Images

All other Images © 2009 Radhika Venkata

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"101 Facts About the Human Body" by Radhika Venkata

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Contents

Please Read This First..................................................................................2

Terms of Use ...........................................................................................................................2

Disclaimer.................................................................................................................................2

Contents............................................................................................................4

About the Author ...........................................................................................9

Our Eyes and Vision....................................................................................10

Why do we have to constantly blink our eyes? ..................................................10

Can our Eye be compared to a Camera? ................................................................11

Why do our eyes water when we cut onions?.....................................................13

Why can't we see well when we go from bright light to a dark room? ....13

Why are people with Color blindness advised not to drive vehicles?........14

Can we walk straight with our eyes closed?........................................................14

How do our eyes interpret a moving object in a movie? ................................15

Where do we get the water for our tears when we cry? ................................15

Why are tears useful? ...................................................................................................16

Is crying necessary? ......................................................................................................16

What is the advantage of having two eyes? ........................................................17

How do our eyes distinguish different colors?....................................................17

What determines your eye color? ............................................................................19

What is long-sightedness? ..........................................................................................19

What is Short sightedness? ........................................................................................20

What is Astigmatism?....................................................................................................21

Our Ears and Hearing.................................................................................23

Why do some people get pain in their ears in an aircraft? ............................23

Is there a Hammer in our body? ...............................................................................24

How do we hear?.............................................................................................................25

Taste.................................................................................................................28

Why can't we appreciate tastes if our mouth is dry?.......................................28

Which part of the tongue is sensitive to different tastes?.............................28

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Smell.................................................................................................................29

Why can't we smell the same odour after a while? ..........................................29

Blood and Circulation.................................................................................30

Why should we avoid sitting too long? ..................................................................30

Why do you sometimes feel dizzy when you get up?.......................................31

What are the Odd Artery and the Odd Vein in our bodies?............................31

How does our body stop bleeding from a cut?....................................................34

Which organs in our body get the most blood? ..................................................35

Why does your heart beat faster when you run?...............................................36

Why is Blood red in Color? ..........................................................................................36

What do I need to know about Hemoglobin? ......................................................37

Who are the universal donors and universal recipients? ...............................38

Why do we feel 'pins and needles' are in our arms and legs?......................39

Breathing and Related Topics.................................................................41

Why can't people breathe and swallow at the same time? ...........................41

Cells ..................................................................................................................42

Are all cells in our body the same?..........................................................................42

Which specialized part of a cell is called the 'Powerhouse”? .......................43

Can the cells in our body talk to each other? ......................................................44

Digestion and Nutrition.............................................................................47

Why are some of our teeth shaped differently from others?........................47

Why do the 4 types of teeth have different shapes?........................................47

Should you take water soluble vitamins every day? ........................................48

Why do we have to chew our food properly? ......................................................49

Why do sportsmen eat bananas during their strenuous activity? ..............49

Why can't some people eat dairy products? ........................................................50

Where do we get our energy if we skip our breakfast and lunch? .............51

Why do you hear growling sounds when you are hungry?............................51

What causes bad breath?.............................................................................................52

Is belching inevitable after eating?.........................................................................53

Skin and Related Topics............................................................................54

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Why do we get pimples? ..............................................................................................54

Why does our skin wrinkle in our old age? ..........................................................54

What is the largest organ of the human body? ..................................................54

Why is clipping our nails painless though it is growing tissue? ..................55

Why are boils dangerous in the central area of the face?..............................56

Why do hot things burn the skin? ............................................................................56

Why does burnt skin become white? ......................................................................56

Why do we get “goose bumps”? ...............................................................................57

Why do our lips, palms and soles get chapped in cold weather?................58

Hygiene and Related Topics ....................................................................59

Why should we wash our hands with soap before eating?............................59

How are germs killed in our body? ..........................................................................59

Skeleton and Related Topics ...................................................................62

Can people get shorter in the evenings?...............................................................62

Why are bone fractures more common in old people? ....................................62

What is a collar bone?...................................................................................................63

Why are our bones so strong? ...................................................................................63

Why is the first vertebra called the 'Atlas'? .........................................................64

What are Sesamoid bones?.........................................................................................65

What might happen if we didn't have a skeleton in our body?....................66

What does, “Muscles act as Agonists and Antagonists to carry

movements” mean? .......................................................................................................67

Why does a child have more bones in their body than an adult?................68

What is the smallest bone in the body?.................................................................69

Internal Organs and Related Topics.....................................................71

What is 'The Master gland' in the human body? ................................................71

Why is our urine sometimes yellow? ......................................................................71

How does a doctor measure your heart rate? .....................................................72

How and why does your doctor listen to our heart sounds?.........................73

Are there millions of germs in our intestines?....................................................75

How are waste products removed from the body? ...........................................76

Are stones actually formed in the body?...............................................................76

Is the absorption surface of a small Intestine as big as a Tennis court? 77

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Can the acid in our stomach dissolve razorblades? ..........................................78

What is an Appendix?....................................................................................................79

Health and Related Topics .......................................................................81

Is sun light enough for your daily dose of Vitamin D? ....................................81

Should you take water soluble vitamins every day? ........................................81

Why is cigarette smoking bad? .................................................................................82

Is sneezing a good thing?............................................................................................83

Are Hiccups dangerous?...............................................................................................84

Why do you get Vaccinations (shots) from your doctor? ...............................85

Why is Cancer compared to a Crab?........................................................................85

Men, Women and Related Topics...........................................................87

Why are men affected by baldness more than women? .................................87

Do men have a uterus (the sac that holds a developing baby)? .................87

What determines the sex of a person?...................................................................88

Why are children’s and women’s voices softer than males?.........................89

Can some diseases affect only boys and men?...................................................90

Our Brain and Related Topics .................................................................92

Why does the brain use a larger area for hands than our whole trunk?..92

Why cannot our brain feel pain?...............................................................................93

So, why do we get headaches? .................................................................................93

Why can't we move our ears towards a sound like animals do?.................94

Which part of our Brain determines our personality?......................................94

Other Questions ...........................................................................................97

Is the right side of our body bigger than the left side? ..................................97

Why are our fingers not equal in size?...................................................................97

Why do some people have flat feet? .......................................................................98

Why do we stop growing at a certain age? ..........................................................98

Why do we feel sleepy after a meal? ................................................................... 100

Why do your grandparents have gray hair?...................................................... 100

Do we need our belly button? ................................................................................. 101

Does the human body generate electricity?...................................................... 101

Why do people shiver in cold weather? .............................................................. 102

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Which of our five fingers is most important? ................................................... 102

Why are some Twins not identical?...................................................................... 103

Does our body have Living tissue with NO Blood supply?........................... 104

Why is it easy to wake people in early mornings? ......................................... 105

A Few Words from the Author ..............................................................106

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About the Author

Dr. Radhika is a Pathologist by profession and likes to share her medical

knowledge with others.

She loves to spend time with family and her computer.

She used many of the questions asked by her own two children as the basis

for this, her third book published by eBookwholesaler.

She wrote '101 Facts About the Human Body - Simply Explained and

Illustrated!' for you to learn from and to share with your children, so that

they have accurate information to help them be comfortable with their own

bodies and understand why it is so important to eat the right foods, exercise

and generally look after themselves.

Dr Radhika has also studied Web design using the php/MySQL language. Dr

Radhika has also studied Web design using the php/MySQL language. Her

current project is her website, http://www.pathology-world.com/

Dr Radhika's favorite saying is, "God doesn't require us to succeed; he only

requires that you try" - Mother Teresa

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Part I: Our Senses

Our Eyes and Vision

Why do we have to constantly blink our eyes?

We blink our eyes about once every five to seven seconds. Mostly, we don't

even know that we are blinking our eyes.

If you deliberately keep your eyes wide open for a few minutes and stop

yourself blinking, your eyes will start to feel like they are dry after a while.

You will feel this dryness when you are watching your TV or computer and

forget to blink.

If you do not blink, then your eyelids cannot smear the tears from lacrimal

glands and oily secretions from your 'meibomian glands' over the eyeballs to

keep them moist.

There are some glands called 'meibomian glands' under your eyelids. The oily

secretions from these glands mix with tears and keep a moist layer on the

eyes.

This moist layer prevents the surface of your eyes becoming dry. If the eyes

are dry, the conjunctiva (white part of the eye) and the cornea (black area in

the centre of your eye) may become damaged and get infected.

Also, when we blink, the eyes are protected from dust being deposited on our

eyes.

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You can see the tiny meibomian glands in both the upper and lower

eyelids in my picture. There are more in the upper eyelid.

They keep the eyes moisturized by producing an oily secretion and releasing

it onto the eye through tiny ducts.

What happens to the eyes when they are dry? When the conjunctiva and

cornea remain dry for some time, small areas of the surface become eroded.

If not treated, they will get infected. When the eyes get dry and don’t get

any tears or secretions, it is called 'xerosis'.

If you stay in open places where there is lot of wind, you need to blink more

often than usual to stop the drying effect of the wind on your eyes.

Can our Eye be compared to a Camera?

When you go to a picnic or a party, you might take your camera with you to

get pictures of you and your friends. Right?

But, do you know you have TWO CAMERAS in your body?

They are your eyes! Each eye acts like a camera. In the same way that you

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focus your camera on the subject and click the button to get the image on

the film, you focus your eye on the subject and get the image on the retina.

Here is a picture that compares the parts of human eye with a camera:

In the picture, both your eye and your camera focus on the object

and get the picture on to the retina (eye) or screen (camera).

1. Light coming from the subject into the camera and eye.

2. Light passing through the camera opening and pupil of the eye.

3. The lens of the camera and the lens of the eye focus the image on

to the screen and retina respectively.

4. A picture is created on the film and the retina. This picture will be

small and inverted (upside down).

Comparing camera and eye:

Pupil of the eye = Opening of the camera (Light passes through)

Lens of the eye = Lens of the camera (Focuses on the subject. We adjust the

camera lens. The lens in the eye is adjusted by the process called

'accommodation')

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Retina of the eye = Film of the camera (Picture image is created)

Why do our eyes water when we cut onions?

There are sulphur compounds in the onion which irritate our eyes.

When we cut the onions, we damage the cells of the onion. The Synthase

enzyme in the onion cells comes in contact with amino acids called

sulfoxides. These sulfoxides

are converted into Sulfenic

acid.

This unstable sulfenic acid

changes to propanethiol-S-

oxide gas which forms mild

sulphuric acid when it mixes

with the moisture in our

eyes. This acid irritates the

eye and our lacrimal glands

produce tears to wash out

this irritant.

To reduce the irritation, wash

your onions under water.

Why can't we see well when we go

from bright light to a dark room?

Our eyes have two types of receptors in the retina.

1] Cones for seeing color. When we go into a lighted area, the cones provide

our vision; the colors and the objects are bright. This type of vision by the

cones is called ' Photopic vision'.

2] Rods for night vision. When we are in a dark area, the rods provide vision

called ' Scotopic vision'; we see things as grey or black and cannot

appreciate the details or colors of objects in the dark.

When we move from bright light to a dark area, we can't see very well for a

while because the rods adapt more slowly than the cones. It may take from

25 to 60 minutes for the rods to get their full functionality.

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So, it will take few minutes for us to see well in the dark. This is called ' Dark

adaptation'.

But, cones get to work more quickly. If we move from a dark area to a light

area, most people can see well almost instantly.

Why are people with Color blindness advised not to

drive vehicles?

A person with color blindness cannot recognize certain colors. The most

common color blindness is 'red-green color' blindness. Nine percent of the

male population has some sort of red-green blindness.

Red-green blindness is inherited as an 'X-linked' disorder. This means that it

only occurs in the male.

An opthalmologist uses a set of color plates, called Ishihara Charts, to detect

color blindness. With most of the pictures, people that have normal vision

see a particular number in the chart. When someone gets a different result

from looking at the plates, the specialist can work out what type of color

blindness the patient is showing.

If people have a problem with color differentiation of red and green, it will be

difficult for them to see the colors of traffic lights.

Some people think that they can compensate for that deficiency because

they are familiar with the position of the lights; red on the top, yellow in the

middle and green at the bottom. If the intensity of the light changes, then

they will know which traffic light changed.

But, it would be dangerous for them to drive when away from their original

surroundings or under stress, and they would be a risk to other drivers too.

Can we walk straight with our eyes closed?

Probably not, unless the person is trained to do so.

A person’s balance depends on three factors.

1. Vision: Vision helps us to adjust our body to the environment. We use

our eyes to see the objects, set a target and direct ourselves on a

straight path.

2. Inner ear: There is a part called 'vestibular apparatus' in the inner

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ear. It maintains the body balance by sending information of our body

position with respect to gravity.

3. Proprioceptors: There are many receptors in our joints, ligaments

and muscles. These receptors send signals to the brain continuously so

that we know the position of our body parts in relation to each other.

These three factors work together to maintain our body balance so we don't

fall or do any un-coordinated movements.

Why can't we walk straight?

If any of the above three systems are damaged or not used, the person

tends to sway from the straight line. For example, if a person closes his eyes,

they cannot walk straight unless they have had special training. Most people

tend to move towards the right side of the straight line if they close their

eyes and try to walk straight.

How do our eyes interpret

a moving object in a movie?

How can our eyes see a person moving on a TV screen or in a movie theatre

screen even when the film strip has still images of the person?

This effect is called 'critical fusion frequency'. (Ref. Ganong - Physiology).

Critical fusion frequency is the rate at which the frames of a film are

interpreted as separate images. When the images are displayed to you more

rapidly, you no longer perceive separate frames and the object seems to be

in continuous motion.

This principle is used to make movies. The normal rate is 24 frames per

second. If we see 24 frames showing a puppy in one second, we will

appreciate them separately. If we see 50 photos of a puppy in one second,

the retina cannot separate them, so it looks like the puppy is moving.

Where do we get the water for our tears when we

cry?

When a person cries or if he laughs too much, tears comes out of the eyes.

Where are they coming from?

There are small glands called 'lacrimal glands' on the outer top corner of the

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eye. These glands actually produce tears and store them there. When we cry,

the muscles around these glands squeeze the glands. The tears are secreted

through the fine duct over the eye.

Lacrimal gland that produces tears.

Why are tears useful?

With every blink, tears are spread over the eye surface of our eyes from our

lacrimal glands. This keeps the cornea moist and prevents it from drying.

Tears have anti-bacterial properties which keeps the germs away from the

eye surface.

Is crying necessary?

Scientists have been doing research on crying for many years, asking

questions like;

what are the brain pathways controlling crying?

Why and how has crying developed?

One benefit that is well known is that many people feel calm and relaxed

after they cry.

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What is the advantage of

having two eyes?

Looking with two eyes is called

'Binocular vision'. ('bi' means two,

'ocular' means eyes). Put a pencil

down on the table in front of you.

Gently close only your right eye and

look at the pencil.

Now, without moving your head or

the pencil, open your right eye and

gently close only your left eye.

When you do this properly, it will

seem like the pencil appears in a

different position when seen by each

of your eyes.

Now open your both eyes and look at

the pencil. Your brain uses the slightly

different image from each of your eyes to locate the pencil’s position as

accurately as possible.

When the brain receives two images from the two retinas (when both eyes

are open), it processes both images and interprets the depth and distance of

the object correctly. If one eye is closed, the brain receives only one image

from one retina and doesn't have a second image to compare it with. Then,

how you see the object is how it looks in that single field.

People who have poor sight in one of their eyes have difficulties with pouring

coffee into the cup, picking things up, etc. Binocular vision helps you to know

the position of the object correctly.

How do our eyes distinguish different colors?

What happens if we can't appreciate or distinguish different colors?

Everything looks grey, like a black and white movie.

There is a thin layer called the 'retina' at the back of our eyes. The retina has

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two types of cells called:

1. Rods: The rods help you to see when it is dark. There are about 120

million rods in each human eye.

2. Cones: The cones are useful for color vision. They help you to appreciate

all the colors around you. There are about 6 million cones in each human

eye.

The Rods and Cones are activated

by light. Once they are activated by

receiving the light, they send

signals to your brain. The brain

interprets what the object is and

the colors which are present.

About Cones:

There are three types of cones.

1) Short type, or S type, cones

are stimulated by the color

blue which is made of light

rays with a short

wavelength.

2) Medium type, or M type.

Cones are stimulated by the color green which is made of light rays

with a medium wavelength.

3) Long type, or L type, Cones are stimulated by the color red which is

made of light rays with a longer wavelength.

These different types of cones are stimulated at different proportions to get

color or color combinations.

A red apple would stimulate L type cones exclusively.

A green apple would stimulate M type cones exclusively.

A yellow apple would stimulate both L type and M type equally.

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What determines your eye color?

Why do some people have brown eyes, some have blue eyes and others have

green eyes?

The color of your eye depends on the level of a pigment called 'melanin' in

the iris in your eye. Brown eyes have a lot of melanin and blue eyes have

only a little melanin.

If there is no melanin at all in the iris, that person will have very pale blue

eyes. This condition is called 'Albinism'.

There are also some very complex genetic factors which we inherit from our

parents that affect our eye color.

What is long-sightedness?

Long sightedness is one of the common errors with people’s sight where the

rays of light passing through the cornea (lens of the eye) are not properly

focused onto the retina which converts the light into signals which it sends to

your brain. People with this condition (called 'hypermetropia' by doctors) can

see distant objects clearly, but they cannot see near objects as clearly.

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Long-sightedness causes the person’s eye to not focus correctly on

objects that are close. They need to move the object a little farther away to a

point where it will be properly registered on the retina. The picture shows

that the near object is focused BEHIND the retina. An ophthalmologist will

advise this person to wear a 'Convex or Converging lens' which will help them

to focus the light rays from the object properly onto the retina in their eye.

We think that long sightedness may happen when a person’s eyeballs are

shorter from front to back than normal, so that the image does not focus

properly onto the retina. Another possibility is if the lens of a person’s eye is

thinner than normal.

What is Short sightedness?

Short sightedness is, like long sightedness, a type of refractive error. It is

also called 'myopia' by doctors. People with this condition can see objects

which are near them clearly, but cannot see distant objects as clearly.

When a person is short-sighted, near objects are focused correctly on the

retina in their eye but not distant objects. So, they will move that distant

object a little closer to help it be properly focused on the retina.

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In the picture, the distant object is focused short of the retina. So, the

ophthalmologist will advise the patient to wear a 'Concave’ or ‘Diverging’

lens, which will help to properly focus the image on their retina.

We think that near sightedness might be caused when a person’s eyeballs

are longer from front to back than normal or when the lens of their eye is

more curved than usual.

What is Astigmatism?

Astigmatism is another refractive error of the eye. The surface of the cornea

(clear domed structure at the front of the eye) or the lens will have a

different curve to normal and images are not focused properly on the retina.

With this condition, rays from the vertical plane are focused properly on the

retina, but the rays from the horizontal plane are not, so the image which

their brain produces is blurry.

Specialists use specially shaped lenses to correct this error. Most people will

have mild astigmatism that can be easily corrected by a properly prepared

lens.

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Our Senses

Our Ears and Hearing

Why do some people get pain in their ears in an

aircraft?

Have you experienced pain in your ears during a flight or have you seen

somebody with that condition?

Children may cry a lot if they suffer because of this as it is very

uncomfortable.

There is always some air in the middle ear cavity. The pressure of this air is

equal to the pressure of the air in the environment around the person.

The pressure is kept that way by a connection called 'eustachian tube'

between your middle ear and the roof of your mouth.

When we swallow or yawn, our eustachian tube opens up and air goes into

the middle ear.

The eustachian tube connects the middle ear and the roof of the mouth. It

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opens up during yawning, so pressure in the middle ear is equalized with that

of your surroundings.

The pressure in an aircraft changes rapidly, especially when taking off and

landing.

The difference in pressure between the middle ear cavity and your

surroundings makes the tympanic membrane stretch. That causes the pain.

So, you might yawn or swallow several times while your plane is taking off or

landing. People also chew gum or suck on a piece of candy so the eustachian

tube keeps opening and shutting.

Is there a Hammer in our body?

You know that a hammer is a tool used to hit nails in the walls, don't you?

You might have seen a relative using something to push a nail into the wall

or some wood. That is the hammer.

Is there a hammer in our body? Yes, but it’s not much like that big hammer

your relative was using. It is a small, hammer-shaped bone in your ear.

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How do we hear?

1) Sound goes through the auditory canal.

2) That causes the tympanic membrane to vibrate.

3) The tympanic membrane vibrates the three small bones called ossicles

4) The stapes transmits the vibrations to the cochlea

5) The cochlea sends the signals to the brain through the auditory nerve.

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Here is a picture of the ear. Inside the middle ear, you can see THREE small

bones called 'ossicles'.

Malleus: (hammer shaped) bone

Incus: (anvil shaped) bone

Stapes: (stirrup shaped) bone

These three small bones unite with each other to transmit the vibrations from

the tympanic membrane to the inner ear.

The Malleus is attached to the tympanic membrane on one side and the Incus

on the other side.

The Incus is the middle bone between the Malleus and the Stapes.

The Stapes is attached to the Incus on one side and an oval window of the

inner ear.

In the inner ear, the vibrations are processed. Then, signals are sent to the

brain for further interpretation of the sound.

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If these ossicles are damaged by infection or injury, an 'ear, nose and throat

surgeon' will operate to replace the damaged bone with a new piece of bone

taken from elsewhere in the body.

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Our Senses

Taste

Why can't we appreciate tastes if our mouth is dry?

Our tongue has around 10,000 taste buds which are the sensory organs

which detect how things we consume taste. The taste buds are

'chemoreceptors' that detect four kinds of taste; sweet, bitter, salty and sour

in their response to the chemicals in our food.

The receptors need the substance to

be at least partly dissolved in our

saliva which fills the pores of our

taste buds and activates them.

When you have a dry mouth, there

is not enough saliva to bring the

food molecules into contact with the

receptors, so you cannot properly

appreciate the taste of what you are

eating.

The three major salivary glands are

called the parotid, submandibular

and sublingual glands. Most saliva comes from the submandibular and

parotid glands to help keep the mouth moist and assist digestion.

Which part of the tongue is sensitive to different

tastes?

Taste buds are distributed throughout the

surface of the tongue, so any part of the tongue

can appreciate every taste. Certain areas of the

tongue are believed by many experts to be more

sensitive to certain tastes, but this map is not

accepted by some authorities.

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Our Senses

Smell

Why can't we smell the same odour after a while?