Name: 紙巾，第一部分。速成班 A&P #2 (Tissues, Part 1: Crash Course A&P #2)
Uploaded: 2021-01-14T05:32:11.000Z
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Pretty nice. Kind of a rugged, no-frills life form.

虛擬句型

The thing about amoebas is that they do everything in the same place. They take in and digest

their food, and reject their waste, and get through everything else they need to do, all

They don’t need trillions of different cells working together to keep them alive. They

don’t need a bunch of structures to keep their stomachs away from their hearts away

from their lungs. They’re content to just blob around and live the simple life.

But we humans, along with the rest of the multicellular animal kingdom, are substantially

more complex. We’re all about cell specialization, and compartmentalizing our bodies.

Every cell in your body has its own specific job description related to maintaining your

homeostasis, that balance of materials and energy that keeps you alive.

And those cells are the most basic building blocks in the hierarchy of increasingly complex

We covered a lot of cell biology in Crash Course Bio, so if you haven’t taken

that course with us yet, or if you just want a refresher, you can go over there now.

But with that ground already covered, we’re going to skip ahead to when groups of similar

cells come together to perform a common function, in our tissues.

Tissues are like the fabric of your body. In fact, the term literally means “woven.”

And when two or more tissues combine, they form our organs. Your kidneys, lungs, and

your liver, and other organs are all made of different types of tissues.

But what function a certain part of your organ performs, depends on what kind of tissue it’s

made of. In other words, the type of tissue defines its function.

And we have four primary tissues, each with a different job:

our nervous tissue provides us with control and communication,

epithelial tissues line our body cavities and organs, and essentially cover and protect the body,

while connective tissues provide support.

If our cells are like words, then our tissues, or our groups of cells, are like sentences,

And your journey to becoming fluent in this language of your body -- your ability to read,

understand, and interpret it -- begins today.

Although physicians and artists have been exploring human anatomy for centuries, histology

-- the study of our tissues -- is a much younger discipline.

That’s because, in order to get all up in a body’s tissues, we needed microscopes,

and they weren’t invented until the 1590’s, when Hans and Zacharias Jansen, a father-son

pair of Dutch spectacle makers, put some lenses in a tube and changed science forever.

But as ground-breaking as those first microscopes were then, they were little better than something

you’d get in a cereal box today -- that is to say, low in magnification and pretty blurry.

So the heyday of microscopes didn’t really get crackin’ until the late 1600s, when

another Dutchman -- Anton van Leeuwenhoek -- became the first to make and use truly

While other scopes at the time were lucky to get 50-times magnification, Van Leeuwenhoek’s

had up to 270-times magnifying power, identifying things as small as one thousandth of a millimeter.

Using his new scope, Leeuwenhoek was the first to observe microorganisms, bacteria, spermatozoa,

and muscle fibers, earning himself the illustrious title of The Father of Microbiology for his troubles.

But even then, his amazing new optics weren’t quite enough to launch the study of histology

as we know it, because most individual cells in a tissue weren’t visible in your average scope.

It took another breakthrough -- the invention of stains and dyes -- to make that possible.

To actually see a specimen under a microscope, you have to first preserve, or fix it, then

slice it into super-thin, deli-meat-like sections that let the light through, and then stain

Because different stains latch on to different cellular structures, this process lets us

see what’s going on in any given tissue sample, down to the specific parts of each

Some stains let us clearly see cells’ nuclei -- and as you learn to identify different

tissues, the location, shape, size, or even absence of nuclei will be very important.

Now, Leeuwenhoek was technically the first person to use a dye -- one he made from saffron

-- to study biological structures under the scope in 1673, because, the dude was a boss.

But it really wasn’t until nearly 200 years later, in the 1850s, that the we really got the

first true histological stain. And for that we can thank German anatomist

Back in his day, a few scientists had been tinkering with staining tissues, especially

with a compound called carmine -- a red dye derived from the scales of a crushed-up insects.

Gerlach and others had some luck using carmine to highlight different kinds of cell structures,

but where Gerlach got stuck was in exploring the tissues of the brain.

For some reason, he couldn’t get the dye to stain brain cells, and the more stain he

So one day, he tried making a diluted version of the stain -- thinning out the carmine with

ammonia and gelatin -- and wetted a sample of brain tissue with it.

So he closed up his lab for the night, and, as the story goes, in his disappointment,

he forgot to remove the slice of someone’s cerebellum that he had left sitting in the

He returned the next morning to find the long, slow soak in diluted carmine had stained all

kinds of structures inside the tissue -- including the nuclei of individual brain cells and what

he described as “fibers” that seemed to link the cells together.

It would be another 30 years before we knew what a neuron really looked like, but Gerlach’s

famous neural stain was a breakthrough in our understanding of nervous tissue.

AND it showed other anatomists how the combination of the right microscope and the right stain

could open up our understanding of all of our body’s tissues and how they make life possible.

Today, we recognize the cells Gerlach studied as a type of nervous tissue, which forms,

you guessed it, the nervous system -- that is, the brain and spinal cord of the central

nervous system, and the network of nerves in your peripheral nervous system. Combined,

they regulate and control all of your body’s functions.

That basic nervous tissue has two big functions -- sensing stimuli and sending electrical

impulses throughout the body, often in response to those stimuli.

And this tissue also is made up of two different cell types -- neurons and glial cells.

Neurons are the specialized building blocks of the nervous system. Your brain alone contains

billions of them -- they’re what generate and conduct the electrochemical nerve impulses

that let you think, and dream, and eat nachos, or do anything.

But they’re also all over your body. If you’re petting a fuzzy puppy, or you touch

a cold piece of metal, or rough sandpaper, it’s the neurons in your skin’s nervous

tissue that sense that stimuli, and send the message to your brain to say, like, “cuddly!”

or “Cold!” or “why am I petting sandpaper?!”

No matter where they are, though, each neuron has the same anatomy, consisting of the cell

The cell body, or soma, is the neuron’s life support. It’s got all the necessary

goods like a nucleus, mitochondria, and DNA.

The bushy dendrites look like the trees that they’re named after, and collect signals from other