Tissues, Part 4 - Types of Connective Tissues: Crash Course Anatomy & Physiology #5

Summary

This educational video script delves into the fascinating world of connective tissues, highlighting their diversity and crucial role in the human body. It explores various types, including loose and dense connective tissues with subclasses like areolar, adipose, and reticular, as well as tendons and ligaments. The script also covers cartilage, bone tissue, and blood, emphasizing their unique properties and functions. The discussion on how cooking denatures proteins in connective tissues, making them edible, adds a culinary perspective to the biological narrative.

Takeaways

• 🥩 The physical composition of humans is similar to raw meat, with connective tissues requiring cooking to be edible.
• 🍗 Early humans cooked meat primarily to break down inedible connective tissues and make the meat more palatable.
• 🧬 Connective tissues are diverse and include tendons, bones, and fat, all originating from the same embryonic cells.
• 🔬 Connective tissues are characterized by an extracellular matrix rich in fibers, which can be difficult to chew raw.
• 🍗 Cooking meat denatures protein fibers, making them soft and edible, as seen when roasting a chicken and its skin becomes easily separable.
• 🌟 There are four main types of connective tissues: loose and dense connective tissue, cartilage, and bone tissue, each with specific functions and locations in the body.
• 💧 Loose connective tissues, such as areolar and adipose, have fewer fibers and more ground substance, providing flexibility and storage.
• 🏋️‍♂️ Dense connective tissues, including tendons and ligaments, are composed of tightly packed collagen fibers, providing strength and resistance to tension.
• 🦴 Cartilage comes in three types: hyaline, elastic, and fibrocartilage, each offering different levels of support and flexibility depending on the body part.
• 🩸 Blood is a type of connective tissue that connects body parts, transports nutrients, and provides rigidity through its protein-rich plasma.

Q & A

What is the primary reason humans began to cook meat?

Humans began to cook meat primarily to break down connective tissues that are difficult to chew, making the meat more edible.

How does cooking affect the connective tissues in meat?

Cooking denatures the protein fibers in connective tissues, making them soft and pliable, which is easier to consume.

What are the two main subclasses of connective tissue proper and how do they differ?

Connective tissue proper comes in loose and dense subclasses. Loose connective tissue has fewer fibers and more ground substance, while dense connective tissue has more fibers and less ground substance.

What is areolar tissue and where is it commonly found in the human body?

Areolar tissue is a loose connective tissue found all over the body, just under the epithelial tissue and wrapped around organs. It has a loose arrangement of fibers and is good at holding watery ground substance.

What is adipose tissue and what is its primary function?

Adipose tissue is a type of loose connective tissue that is mostly composed of fat-storing cells called adipocytes. Its primary functions include energy storage, insulation against heat loss, and contributing to body shape.

How does reticular tissue differ from areolar tissue?

Reticular tissue differs from areolar tissue in that it has a woven mess of reticular fibers instead of collagen and elastin fibers. It provides a soft internal framework for organs like the spleen, lymph nodes, and bone marrow.

What is the function of dense regular connective tissue in the human body?

Dense regular connective tissue, found in tendons and ligaments, provides great resistance to tension when that tension is exerted in one direction, connecting muscles to bones or binding bones together at joints.

What is dense irregular connective tissue and where is it typically found?

Dense irregular connective tissue has thicker and erratically arranged fibers. It is found in areas where tension might be exerted in many different directions, such as the dermis underlying the skin.

How does dense elastic connective tissue differ from dense regular connective tissue?

Dense elastic connective tissue provides both support and flexibility, containing more elastic fibers. It is found in areas requiring elasticity, such as around joints and in the walls of large arteries.

What are the three types of cartilage and where are they typically found?

The three types of cartilage are hyaline cartilage, elastic cartilage, and fibrocartilage. Hyaline cartilage is found in areas like the rib-cage and the tip of the nose. Elastic cartilage is found in the ear, providing strength and flexibility. Fibrocartilage is found in intervertebral discs and knee joints, withstanding pressure and preventing bone-to-bone contact.

How is bone considered a type of connective tissue?

Bone, or osseous tissue, is considered a type of connective tissue because it is calcified connective tissue that supports and protects the body's structures, similar to other connective tissues which provide support and connection.

What is the role of blood as a connective tissue in the body?

Blood is a connective tissue that connects distant parts of the body and provides rigidity to other parts. It transports cells, nutrients, hormones, and wastes, ensuring all body parts remain connected and functional.

Outlines

00:00

🍗 The Role of Connective Tissue in Our Bodies and Food

This paragraph delves into the physical similarities between humans and raw meat, emphasizing the role of connective tissue in both our bodies and the meat we consume. It explains that while muscle tissues are tender and can be eaten raw, connective tissues require cooking to break down the tough fibers. The paragraph highlights the diversity of connective tissues, which are not just leftovers but essential components with unique structures dominated by an extracellular matrix rich in fibers. The discussion includes how cooking denatures protein fibers in connective tissues, making them more edible, and the various types of connective tissues found in the human body and butcher shops, such as loose and dense connective tissue, areolar tissue, adipose tissue, and reticular tissue.

05:00

🦴 Exploring the Diversity of Connective Tissues and Their Functions

The second paragraph continues the exploration of connective tissues, focusing on dense elastic tissue, cartilage, bone, and blood. It describes how dense elastic tissue provides both support and flexibility, as seen in the spine and large arteries. The paragraph then discusses the three types of cartilage—hyaline, elastic, and fibrocartilage—and their specific functions in the body, such as providing support and shock absorption. The discussion moves on to bone tissue, explaining that it is calcified connective tissue that supports and protects the body, with spongy and compact bone tissues serving different roles. Lastly, blood is introduced as a type of connective tissue, emphasizing its role in connecting the body's parts and transporting essential substances. The paragraph concludes by reflecting on the importance of tissues in forming the body's organs and maintaining overall health.

Keywords

💡Connective Tissue

Connective tissue is a diverse group of tissues that provide support and structure throughout the body. In the video, connective tissue is highlighted as a crucial element that connects various parts of the body and plays a significant role in the body's structure. It is composed of an extracellular matrix rich in fibers, which are essential for its function. The video discusses different types of connective tissues, including loose and dense connective tissues, and their various roles and locations in the body.

💡Loose Connective Tissue

Loose connective tissue is characterized by its more open structure, containing fewer fibers and more ground substance. This type of tissue is exemplified in the video by areolar tissue, which is found all over the body and provides a supportive but flexible framework. The script mentions pulling on the back of the hand to illustrate the presence of loose connective tissue, which allows for movement and flexibility.

💡Dense Connective Tissue

Dense connective tissue, as discussed in the video, has a higher concentration of fibers, specifically collagen, which gives it strength and resistance to tension. Tendons, which connect muscles to bones, are examples of dense connective tissue. The video uses the example of an Achilles' tendon to illustrate the lack of give in this type of tissue, highlighting its role in providing structural integrity.

💡Areolar Tissue

Areolar tissue is a subtype of loose connective tissue that is found just under the skin and around organs. The video describes areolar tissue as having a loose arrangement of fibers and a lot of open space, which allows it to hold the watery ground substance that surrounding tissues need. This tissue's function is crucial for maintaining the health and hydration of the body's tissues.

💡Adipose Tissue

Adipose tissue, or fat tissue, is a type of loose connective tissue that is primarily composed of adipocytes, cells that store lipids. The video explains that adipose tissue serves as an energy reserve, insulates the body against heat loss, and contributes to body shape. It is an essential component of the body's energy storage system and is highlighted as making up about 18 percent of an average person's weight.

💡Reticular Tissue

Reticular tissue is another form of loose connective tissue, but it is characterized by a network of reticular fibers. The video mentions that this tissue provides a soft internal framework for organs such as the spleen, lymph nodes, and bone marrow. It plays a role in supporting developing blood cells and in holding blood in place within many organs.

💡Tendons

Tendons are a type of dense connective tissue that connect muscles to bones. The video describes tendons as having a high collagen content, which makes them strong and resistant to stretching. The script uses the example of chewing on a tendon, explaining that it would be very difficult due to its dense and tough nature.

💡Ligaments

Ligaments are similar to tendons but are responsible for connecting bones to other bones, particularly around joints. The video discusses how ligaments, like tendons, are made of dense regular connective tissue, providing stability and resistance to tension in a specific direction, which is crucial for joint integrity and movement.

💡Dense Irregular Tissue

Dense irregular connective tissue is characterized by thicker, more randomly arranged collagen fibers. The video explains that this type of tissue is found in areas where tension might be exerted in multiple directions, such as the dermis layer of the skin. This irregular arrangement allows the tissue to withstand stress from various angles.

💡Dense Elastic Tissue

Dense elastic tissue is a subtype of connective tissue that is rich in elastic fibers, providing both support and flexibility. The video mentions that this tissue is found in areas that require elasticity, such as around joints and in the walls of large arteries. It enables the body to move and bend without compromising the structural integrity of these areas.

💡Cartilage

Cartilage is a type of connective tissue that is坚韧 and flexible, providing support while withstanding both tension and compression. The video discusses three types of cartilage: hyaline, elastic, and fibrocartilage, each with different compositions and functions. Cartilage is found in various parts of the body, such as the nose, ears, and joints, and it plays a critical role in providing structural support and cushioning.

Highlights

Humans are physically similar to meat in terms of muscle tissue, which can be eaten raw.

Cooking meat is essential to break down connective tissues that are inedible when raw.

Connective tissues are diverse and include materials like tendons, bone, and fat.

Connective tissues originate from the same embryonic cells and are dominated by an extracellular matrix.

Cooking denatures protein fibers in connective tissues, making them soft and edible.

Loose connective tissue has fewer fibers and more ground substance, exemplified by areolar tissue.

Areolar tissue is found throughout the body, providing support and holding watery ground substance.

Adipose tissue is a type of loose connective tissue that stores lipids and insulates the body.

Reticular tissue provides a soft internal framework in organs like the spleen and bone marrow.

Dense connective tissue, like tendons and ligaments, is rich in collagen and resists tension.

Dense irregular connective tissue is found in areas where tension is exerted in multiple directions, like the skin's dermis.

Dense elastic tissue, found in arteries and around joints, provides support and flexibility.

Cartilage is a type of connective tissue that resists both tension and compression, found in structures like ribs and the nose.

Hyaline cartilage is the most common, providing pliable support and found in the ribcage and nose.

Elastic cartilage contains more elastic fibers, allowing for stretchability, found in the ear.

Fibrocartilage is a shock-absorbing tissue found in intervertebral discs and knee joints.

Bone is a calcified connective tissue that supports and protects the body's structures.

Blood is a connective tissue that connects body parts and provides rigidity, composed of cells and plasma.

Erythrocytes, leukocytes, and platelets are the main cell types in blood, each with specific functions.

Tissues form a hierarchy of organization essential for the body's structure and function.

Transcripts

Technically, we’re all just meat.

Yeah, you could say that what makes us human is our emotions, or thoughts, or memories,

but physically, we’re not all that different from this.

We’re used to thinking of meat as the muscle tissue that people cook and eat -- but the

fact is, you could eat that stuff raw. A chicken breast or a steak or a pork chop is tender

enough that it doesn’t need cooking.

What does need cooking is all of the connective tissue that’s in and around the muscle,

and gets in the way of our meal.

So one of the main reasons humans began to roast, and boil, and bake meat in the first

place, was to break down those connective tissues that we can’t chew, so we could get the meat.

Now, you might’ve noticed that connective tissues kind of seem like a grab bag of materials

that don’t really fit in other groups.

Our muscle, nervous, and epithelial tissue types are more uniform, more obviously grouped

together. Sometimes, our connective tissues just seem like the leftovers you throw in the stew pot.

But appearances are deceiving, and our inability as a species to tolerate these tissues in

our food is just one reminder that no matter how different tendon, bone, or a hunk of fat

may appear, they are indeed very closely related.

They all spring from the same embryonic cells, and their structures are dominated, not by

cells, but by an extracellular matrix full of fibers.

And it’s those fibers that have given humans the most trouble in our meat-eating history.

It wasn’t until we figured out how to cook the stuff the that we were able to denature, or

change the natural structure of, those protein fibers so that they became soft and pliable.

Take a chicken for example. You couldn’t just pull the skin off a living bird -- like

ethically you couldn’t do that but also you probably couldn’t.

Its living skin is anchored by connective tissue that’s full of collagen fibers. But

if you roast that chicken, and break apart that collagen, suddenly the skin just peels

right off with no effort at all.

So connective tissues, as evidenced by this mess here, are good reminders of how sometimes

things are more similar than they appear.

They’re also delicious . . . if you’re into that.

So we know what our connective tissues have in common, and we know that we’ve got four

different types -- but what do they look like, what do they do, and where are they found

-- both in your butcher shop, and on your body?

Perhaps your most diverse type is your classic connective tissue proper. It comes in both

loose and dense subclasses, based on how many fibers it has in its ground substance.

Pull on the back of your hand. See that fleshy tent there? That’s one example of loose

connective tissue. There’s a lot of ground substance in here, and the elastin fibers

help it snap back into place, while the collagen helps anchor it so you can’t, like, snag

your skin on a zipper and watch it just fly off.

But try pulling on your Achilles’ tendon, or these wing tendons here, and there isn’t

a lot of give. That’s because a tendon is an example of dense connective tissue, with

a lot more collagen. You could chew and chew and chew on a collagen-dense tendon and never

get anywhere. That’s why butchers trim off most dense connective tissue before selling cuts of meat.

So loose connective tissues have fewer fibers, and more cells and more ground substance.

Areolar tissue is the most common loose connective tissue you have, found ALL over your body,

just under your epithelial tissue, and wrapped around your organs.

It’s got a loose and random arrangement of fibers, with just a few fibroblast cells

that make those fibers. If you look at it under a microscope you’ll see that its most

obvious feature is that it looks like it has a lot of open space in it.

This makes areolar tissue makes it great at holding the watery, salty ground substance

that surrounding tissues draw from.

Your adipose tissue, meanwhile, is your fat tissue, the loose connective tissue that’s in here.

Rather than being mostly ground substance, this one is mostly cells -- adipocytes -- which

store lipids for later use, insulate the body against heat loss, and grow pot bellies and love handles.

The average person’s weight is about 18 percent adipose tissue, and it’s those fat

stores that keep us alive when food is scarce. With no fat stores, you’d die within a few

days of your last sandwich.

Reticular tissue is like areolar tissue, but with a woven mess of reticular fibers -- rather

than collagen and elastin fibers -- hence the name.

This tissue provides the soft internal framework, or stroma, of the spleen, lymph nodes, and

bone marrow, and it supports lots of developing blood cells. Just as your areolar tissue is

a kind of sponge for watery ground substance, your reticular tissue is what holds your blood

in place in many of your organs.

Really, all of these loose connective tissue proper types share an airy dispersal of fibers

... which is why they’re easier to eat after cooking -- and why you can pull cooked chicken skin apart.

On the other hand, you can’t easily rip a tendon or ligament in two, or even chew

it, because it’s made of that dense regular tissue, full of tight bundles of collagen

fibers all running parallel.

You can see how neat and smooth a slide sample looks under a scope, the fibers being those

white, flexible structures. They provide great resistance to tension when that tension is

exerted in one direction.

That’s why you find this tissue in your tendons, which connect muscle to bone or other

muscle, and your ligaments, which bind bones together anywhere you’ve got a joint.

But what if those collagen fibers aren’t all stacked regularly in rows?

Then it forms dense irregular tissue, whose fibers are thicker and arranged erratically

-- it’s found wherever tension might be exerted in lots of different directions, like

the leathery dermis underlying your skin.

And finally, your body has places that require more elasticity than rigidity, like say, around

your joints. That’s where you’ll find dense elastic tissue -- for example, connecting

your vertebrae so that your spine can curve and twist.

Some of our largest artery walls are made of this stretchy elastic tissue, too, which

provides both support and flexibility.

From fat to tendons, connective tissue proper is the most diverse group in this tissue family.

But for the last few minutes you’ve also been watching a different type of connective

tissue bob up and down as I talk -- cartilage

Cartilage doesn’t have any blood or nerves, and it stands up against both tension and

compression pretty well -- it’s that whitish gristle you see at the end of pork ribs or

chicken wings in your grocer’s freezer -- and it’s another thing that you’re not going

to have much luck chewing.

Hyaline cartilage is your most common type -- it’s kind of glassy looking and provides

pliable support. It connects your ribs to your sternum and keeps the tip of your nose all perky.

Its ground substance is rich with those sticky, starchy proteoglycans, and although it has

collagen fibers, when you look at it under a scope, you can’t really see them -- instead

the tissue looks glassy, hence the name “hyal” meaning glassy, or transparent.

Elastic cartilage is very similar to hyaline, but with more elastic fibers that are easier

to see, and it’s found in places where strength and stretchability are needed. Like, it’s

why I can pull on my ear without it ripping off.

And just as your body needs firm parts and stretchy parts, it also needs shock absorbers.

That’s where your fibrocartilage comes in. It’s dominated by thick fibers of collagen

and is good at withstanding lots of pressure, so it makes up the discs between your vertebrae,

and your knee joints where it keeps your bones from grinding together.

And speaking of bones!

Although you might not think of something so hard and durable as living tissue, bones

definitely are.

The word “bone” can refer to an entire organ -- like your femur or scapula -- or

just bone tissue. And that bone, or osseous tissue, is just calcified connective tissue,

perfect for supporting and protecting your body’s various structures.

Spongy bone tissue is typically found in the heads of long bones and in the inner layer

of flat bones like the sternum. This spongy tissue is strong, but porous, even to the

naked eye, and it uses this extra room to make and store bone marrow.

Compact bone tissue on the other hand is quite dense, with no visible spaces. It forms the

external layer of your bones and stores calcium for bone cells to use to make more tissue.

Now, if bone doesn’t conjure up your traditional image of a tissue, blood probably doesn’t

either -- I mean, it doesn’t seem to connect things, or lend support, and yet, blood is

our fourth type of connective tissue.

And when you think about it, it clearly does connect distant parts of your body and provides

some rigidity to other parts.

Just like other connective tissues, blood develops from mesenchyme and is made up of

cells surrounded by an extracellular nonliving matrix: In this case, the ground substance

is your blood plasma, which has protein fibers floating around in it.

Your blood’s main job, of course, is delivering goods -- it transports cells, and nutrients,

and hormones, and wastes, and all kinds of other stuff, keeping all the parts of your

body connected in the process.

Most of your blood cells are erythrocytes, or your famous red blood cells that zoom around,

carrying oxygen and carbon dioxide through your body. You’ve also got larger, infection-fighting

white blood cells, or leukocytes in the mix, and your platelets, the small cell fragments

needed for blood clotting so that a paper cut doesn’t bleed you dry.

Unlike other connective tissues, it doesn’t really have what you would call fibers, but

instead has a bunch of protein dissolved in the plasma, and those protein molecules will

form fiber-like structures when your blood needs to clot.

So. You take your four primary types of tissues, and all of the subtypes of each that’s taken

us weeks to explore, and you can probably see how they can come together in many, many

combinations to form all of your body’s organs.

And just like that chaotic cafeteria packed with middle-schoolers -- we’d be hopeless

messes without our hierarchy of organization, our inner and outer boundaries, and the ability

of our systems to communicate with each other.

THAT is what our tissues do for us, and we wouldn’t exist without them.

Today we wrapped up our four-episode series on tissues, with a survey of the sub-groups

of loose and dense connective tissue, including areolar, adipose, reticular, tendons, ligaments,

dense irregular, and dense elastic tissue. We also talked about the three cartilage types,

spongy and compact bone connective tissue, and how and why our blood is also a connective tissue type.

Thanks to all of you for watching, especially to our Subbable subscribers, who make Crash Course

possible to themselves and also to the rest of the world. To find out how you can become a supporter, you

can go to Subbable.com. And don’t forget to go to Youtube.com/CrashCourse and subscribe.

This episode was written by Kathleen Yale, the script was edited by Blake de Pastino,

and our consultant is Dr. Brandon Jackson. It was directed by Nicholas Jenkins & Michael

Aranda and our graphics team is Thought Cafe.