Inside the Living Body Page #3

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

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