Inside the Living Body Page #4

girls become women, boys become man

male brains also release kisspeptin during puberty

the flood of new hormones stimulate the testicles to stop producing sperm

The testicles also generated 10 fold increase in testosterone

the hormone that turns boy into a man

The larynx opens upon to its forward

the vocal cords stretch wider

the longer cords vibrate at a lower pitch

The voice deepens

Testosterone also stimulates the growth of body hair

and doubles muscle mass

These are changes we can see and hear

but we're changing inside too

In the brain ,nerve cells undergo extensive ????

The result is a transformation of our mood and character

Both sexes suffer of torrent of new emotions

and one new emotion ,bigest them all

For the first time, both sex is finding other sex,

attractive

From the inside out , our bodies are overwhelmed with new sensations

our pulse raises, our blood pressures rises

Our lips gorge, our cheeks flash with blood

These're all signals that we desire someone

And sometimes that desire turns out to be mutual

In adolescence, another major life milestone

our first kiss

In the first 2 decades of life

the human body accomplishes something close to miraculous

We're nearly 4 times our orginal height

We're 21 times heavier

we've digested nearly 9 tons of food

our heart has beaten over billion times

and our lungs have drawn 200 million breath

Finally, we're ready, in mind and body ,to become an adult

From "teens" to "twenties

the rapid growth of childhood and puberty

gives way to a new phase of life

adulthood

The 20's are our peak years, both outside and inside

Our body stops growing taller

but it'll never stop changing

trillions of cells make up Our organs and tissues

over time ,these wear out or get damaged

New cells grow and divide to replace old ones

Over time, whole organs are renewed

we get vaguely a brand new body, every 2 years

Some tissues regenerate even faster

That's why we need to come here,for our hair and nails

hairs are made from modified dead skin cells

Each hair grows from a hair follicle embedded in the skin

the Modified cells grow here

then die as new cells push them up????

we grow an incredible 11 km of hair over our whole body every year

Our hair grows, whether we want it to or not

However, other parts of our body

are partially under our control.

choices we make now, like taking exercise

affect us for the rest of our lives

exercise strengthens the heart,

it's the body's hardest working muscle

Exercise also makes our heart muscle more efficient

each contraction pumps more blood

so the heart can beat slower

it's a similar story in the lungs

Exercise stimulates extra capillaries to grow

so we absorb more oxygen with each breath

we Also inhale bigger breath

so every tiny air sack in the lungs gets filled

The surface area of all these sacks is huge

if u lay them all flat, they would cover a tennis court

working out also strengthens our skeleton

exertion puts pressure on the bones

that encourages the bone cells to renew bone fibers

Specialized cells called osteoclasts

eat out way all the damaged bone

other cells - osteoblasts

rebuild it with newer,stronger material

The result, dense, strong bone

At the same time

Our muscles also build

This is a new imaging technique that combines the highest resolution ct-scans

with cutting edge computer power

it's called Volumedic

And it shows how

over 650 skeletal muscle

make up to a thirth of our adult body weight

muscles are made up from bundles of fibers

a good work out rips these fibers apart

When our cells repair the damage afterwards

they add extra material

The muscles grow back bigger and stronger

through choices we made

unfortunately, some choices are less beneficial

Some choices expose us to damage

that even our youthful cells cann't repair

parties are part of life in your twenties

we all know smoke can damage the lungs

But the smoke is not the only hazard here

From the day we were born, our ears have been gradually damaged by loud noise

The problem is deep inside the ear ,past the ossicle bones, inside the cochlea

These fine hairs, the stereocilia, turn sound into nerve impulses

they are very fragile

Loud noise destroys these irreplaceable cells

the hairs that respond to high frequencies, almost affected

possibly because loud, high pitch sounds,

shape their foundations more violently

The effect's still too small to notice

but the frequencies range of our hearing is already shrinking

Another source of damage is - alcohol

though social drinking is very much part of growing up

alcohol is a poison

As we absorb it into our bloodstream

it affects both our organs and our state of mind

afew drinks raise the heart rate and blood pressure

it makes us feel relaxed

we lose our inhibitions and our fine coordination

These sensations are the result of chemical reactions

inside the brain

especially in this region - the cerebellum

the region responsible for the coordination and balance

Alcohol causes a chemical imbalance in the neurons

While some synapses except signals more often, others become blocked

and the more we drink, the more the synapses are affected

Alcohol also fools the brain to thinking we've drunk too much water

it senses the kidneys into overdraft

expelling valuable liquid into the bladder

we may not feel dehydrated now

but the next morning is a different story

After a party, it's the liver that clears up the mess

The liver is the body's biochemical control center

it Performs over 500 functions

One of them's to convert poisons into harmless chemicals

one of the poisons is alcohol

The process demands water

and the liver doesn't care where it takes it from

the brain is 75% water

When the liver demands water, it's the brain that suffers

Water and essential minerals are sucked out and the brain shrinks away from the skull

We experience a very particular kind of headache - a hangover

The best cure - drink some water

Time passes and we get to know our limits

now new challenge is around horizon

It is time to find love and have children of our own

Many of us meet our future partner at work

We may think the attraction is social or physical

but alot of it is biological too

We use our eyes to size up our date

but looks aren't every thing

attraction is also about smell

Inside our nose, the olfactory nerves do more than detect smells

They also detect chemicals we can't smell

pheromones

odorless hormonal messengers we release in our sweat

Pheromones are much more than the body's natural perfume

they carry detailed information about our genetic health

and our ability to resist disease

Our brains detect these signals

and help us choose a partner with the best possible genes

But love - is not just an emotion

It's a bond chemistry!

When we see a partner, we release adrenaline into the blood

our heart pounds, we can't sleep

And then as we get closer and more involved

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