Inside the Living Body Page #2

When vibrations pass through, the hairs vibrate

at the top - low-frequency hairs ,

at the base - fragile hairs to high frequency sounds

Each one 200 times thinner than a hair on our head

Over time, loud noises will damage these hairs

but at this age, they are perfect

our hearing will never be this good again

for eye sight, the story is different

The world is blurred and without color

Our eyes're around the develop

we can't pointerize where we ???

and a imature lenses can not focus

The lens flips the image it receives,

our brains corret the image later

Babies can't yet see in color

because the retina, the screen in the back of the eye,

is also immature

the retina has two types of special cells: rods and cones

They turn light into electrical signals

the ones to detect color, the cones are still developing.

so we see almostly in black and white

From the retina, the signals travel along 2 thick nerves

to the back of brain where we process visual information.

When the image arrives, the real challenge begins

Our immature brain has not yet learned to interpret the data

that's changing fast

by 2 months, we can distinguish colors and shades

At 4 months we can identify facial patterns

and by 8 months , we have 20/20 vision

baby's eyes undergo another amazing change

When we're born, our eyes are blue

but gradually cells of the iris begin making pigments

the iris changes into striking pattern of color

a pattern that is unique to each of us.

We're changing in other ways too

over the first 3 months,

we grow by 25% of our orginal body weight every month

fortunately, that growth rate slows

If it did't ,we would all wiegh a frightening 134 tons by 4th birthday!

around the same as a blue whale

At 8 months, all our sense is working properly

we're begining to explore the world

and the sense we use most - is touch

When we touch something, receptors in our fingertips send

the electrical impulses through sensory nerves in our skin,

upon arms , along the spinal cord and in to the brain

The impulses travel fast, 320 km / hour

Sometimes even this is too slow

the body reacts to painful sensation, like a exteme heat,

by a taking a shortcut

The spinal cord intercepts pain messages

and immediately sends back a reflex response

and we move out away

We have sensory receptors all over our skin

but some areas are more sensitive than others

The hands, face and mouth

there are 9,000 sensory receptors on the tongue alone

this is why, babies use their mouths to explore the world

There is another reason for all our gnawing

our baby teeth are coming through

milk teeth formed deep in the gums while we're still in the womb

Now one by one, they are bursting through

It's painful, but it is progress

at last we can eat solid food

Digestions start in the mouth

The teeth grind up the food

next, special glands, under the tongue , pump out saliva

it Helps break down food

Saliva also lubricates the food

on its 12 hours , 4 meters journey through the gut

it'll Pass from the stomach into the small intestine

and finally the large intestine

waves of contracting muscle keep up food move through out journey

in a process call peristalsis

The contractions are so powerful , we can even eat upside down

This is a unique view of where the food is heading

For the first time,

a new camera shows a high definition view

of the journey through our stomach

Food enters the stomach through a hole at top

The stomach is a bag of muscle

it churns, squashes and squeezes the food into liquid

At the same time, acid breaks down the food

The acid is so corrosive

the stomach continually coats its interior walls with mucus for protection

Without it, stomach ulcers would form

After about an hour, the stomach squeezes the broken down food

through a tiny hole called the pyloric sphincter

The food enters the small intestine

a 3 and half meter coil of tube

This is where we absorb most of nutrients.

First, the pancreas pumps out juice that neutralizes the stomach acid

then bile from the liver breaks down the fat into tiny droplets

Smaller droplets are easily for intestine to adsorb

The interior wall of the small intestine

is lined with million of microscopic projections called villi

These increase the surface area of the gut,

making it easy to absorb nutrients

After an hour and a half,

the small intestine has absorbed most of the nutrients

from the food

What's left, enters the large intestine through this,

the ileocecal sphincter

it's a valve that prevents our food going back

there are few nutrients left to absorb Now

the large intestine's main job is to extract water

What remains is a mixture of waste food , dead cells

and lots of bacteria

these bacteria in the large intestine aren't infection

they produce enzymes that break down complex carbohydrates in our food

carbohydrates we couldn't have ???

Finally, after about 12 hours we expel what remains of the meal

by the age of one, we start to interact with our world

We're more independent from our mothers

and now we can crawl, we begin to explore the world on our own

We can crawl because our bones have got stronger

they need to be, we're getting pretty heavy

at birth, our skeleton is mostly cartilage

the same material, our ears're made of

Cartilage is flexible, it what ables us to squeeze through the birth canal

But after birth, our soft skeleton is a problem

cartilage is too weak to support the growing body

and protect vital organs

so it gradually hardens into bone

Cells called osteoblasts

???? minerals that turn soft cartilage

into hard bone

Some bones also fused together

When we are born, we have gaps between the plates of our skull

These allowed the skull to deform during birth

gradually close until our skull is finally complete

As a skeleton develops, so these desire to get around

We're about to hit one of the major milestones in our life

learning to walk

The key to walking isn't strength

it's balance, and the secret to standing

is hidden deep inside the ears

Behind the ossicles,the bones used for hearing,

there are 3 looping structures

Each loop is about the size of small coin

and oriented in 3 planes

These semicircular canals are part of the ear

but have nothing to do with hearing

they're filled with liquid and they work like a spirit level

they Tell us what's up and what's down

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the hair send data to our brain about how we are oriented

and our direction of movement

they help us balance and stand on two feet

And once we've mastered balance,

we're one step closer to learning to walk

Now there is no limit on where we can go

and what we can do.

From a baby to a toddler

We're about to begin our formative years

A time when we'll put our growing brain

and developing a new system to the test

From infancy to childhood

we're still growing fast

and learning to stand on our own two feet

next is a uniquely huge challenge

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