Name: 免疫系統如何確實運作（How The Immune System ACTUALLY Works – IMMUNE）
Uploaded: 2021-09-06T03:49:17.000Z
Duration: 10 min 48 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

The human immune system is the most complex biological system we know, after the human brain,

and yet most of us never learn how it works.

Your immune system consists of hundreds of tiny—and two large—organs.

It has its own transport network spread throughout your body.

Every day, it makes hundreds of billions of fresh cells organized like an army.

With soldiers, captains, intelligence officers, heavy weapons, and crazy suicide bombers.

Your biology protecting you from the billions of microorganisms that want to consume you,

and from your own perverted cells that turn into cancer.

It's so manifold that it's impossible to cover in one video,

so we'll make a series looking at different aspects of it.

Today: What happens when your body is invaded

and your first lines of defenses are engaged in a fight for life and death.

when suddenly the world explodes and an asteroid rips the sky open.

ready to destroy cities and infrastructure, and eat civilians...

You look at your bleeding thumb that you just cut on a dirty twig in the park.

But inside the wound, a horrible catastrophe has happened.

There are dead cells, and blood and dirt everywhere.

Even worse, countless bacteria invade the warm caverns between your helpless cells

to explore their new home, steal your resources, and poop everywhere.

Immediately, the first stage of your defense kicks in.

The cells that survive the impact, or are hurt or dying, scream in panic

releasing an onslaught of chemical alarm signals that awaken your immune system.

The first cells to show up are macrophages.

If an average cell were the size of a human, a macrophage would be the size of a black rhino.

A stoic cell in principle but you wouldn't want to annoy it.

Within seconds, the large cells attack and begin killing them without mercy.

They stretch out parts like the arms of an octopus,

and grab the bacteria to swallow them whole and digest them alive.

A macrophage can eat 100 bacteria before it's exhausted.

But there are too many enemies, so the macrophages call for reinforcements.

In your blood, hundreds of thousands of neutrophils pick up their signals and move to the battlefield.

Neutrophils are intense suicide warriors that only live to kill.

They're so enthusiastic about killing that they kill themselves a few days after birth,

so they don't have time to accidentally destroy your body from the inside.

As soon as neutrophils arrive, they begin vomiting deadly chemicals at bacteria, or devour them.

They are so careless in their attacks that they are causing real damage to your own cells.

But collateral damage is not their concern now,

Some neutrophils go so far to push their suicide button and explode,

casting a wide and toxic net made from their own DNA filled with deadly chemicals that trap and kill bacteria.

Sometimes, they can continue fighting after that, even though they're sort of dead already.

While the battle rages, your blood vessels let fluid stream into the battlefield like a dam opening up towards a valley.

Your thumb swells up a little and gets red and warm.

The fluid brings a silent killer into the battle zone, millions of complement proteins.

A sort of automated liquid weapon that stuns and kills bacteria by ripping holes into them.

We made a whole video explaining them in detail.

If things go well, your first line of defense kills the invaders quickly.

But sometimes, the enemies are too strong and would overwhelm your defenses eventually,

which means certain death for you, the human.

This is the hour of the dendritic cell, your immune system's intelligence officer.

While your soldiers were bashing in heads,

it was collecting samples by ripping bacteria into tiny parts and covering itself in it.

Like a soldier decorating itself in the guts of a dead enemy.

The cell leaves the battlefield and enters the superhighway of your immune system

that connects all your tissues with your immune headquarters.

The dendritic cell coming from the battlefield is looking for a helper T cell,

which is a sort of all-purpose commander cell within your immune army.

One that happens to have just the right weapon for the bacteria that infected your wound.

So it goes around and rubs itself, still covered in bacteria parts, against every helper T cell it meets.

Most T cells are a bit disgusted and not interested.

A helper T cell recognizes the bacteria parts.

This cell is the weapon that's needed right now.

The dendritic cell is overjoyed and activates the helper T cell.

How come your immune system has a cell that has a weapon against the specific bacteria that infected you?

Well, your immune system has a perfect weapon against every possible disease in the universe.

Against the Black Death, the Coronavirus, or an infection that will emerge in 100 years on Mars.

We'll talk about this a bit more in the next video because it's very complex.

So, for now, just know that you have billions of unique helper T cells

that each have weapons against every possible enemy.

After the right T cell is activated, your second line of defense awakes

and rises like a teenager that needs to get up on a school day...

Your heavy weapons are incredibly effective but they're not fast.

The activated helper T cell begins to clone itself over and over again.

One becomes two, two become four, until there are thousands of them.

The first group quickly moves to help out your soldiers.

At the battlefield, things are getting out of hand.

After fighting for days, it just wants to go to sleep like many of its buddies have done already.

One of them comes to the tired macrophage and whispers something using special chemical signals.

In a heartbeat, the demoralized soldier feels fresh again.