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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

heat.

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.

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

painful?

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

grows.

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

face?

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

motion.

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

removed.

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

eating?

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

hands.

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

clean.

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

clean.

* 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 -

Lymphocytes

Macrophages

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Lymphocytes are classified as:

T-lymphocytes

Helper T-lymphocytes

Killer T-lymphocytes

B-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

cells.

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

disc'.

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

restricted.

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

'hydroxyapatite

crystals' and collagen.

Both make bones

strong. 99% of our

body's calcium is in our

bones.

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

vertebrae.

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

skeleton'.

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

cage).

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

diaphysis.

In a newborn baby

or a small child,

the epiphysis at

each end is

separated from the

diaphysis in the

middle by growth

plates.

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