Study Note
This lecture introduces the role of connective tissue, emphasizing its importance in maintaining the structure, function, and integrity of the body. It uses the tragic death of athlete Flo Hyman, who had undiagnosed Marfan Syndrome, to explain how genetic disorders can affect connective tissue, causing life-threatening conditions like aortic tears. Connective tissue, which includes proper connective tissue, cartilage, bone, and blood, is vital for providing support, protection, and transportation within the body. The extracellular matrix, made of ground substance and fibers, plays a significant role in giving connective tissues their properties. Connective tissues are formed from cells in different stages of development, such as blast cells, which produce the matrix, and cyte cells, which maintain it. Additionally, the immune functions of connective tissue, including macrophages and white blood cells, are discussed.
20 Main Ideas
1. Connective Tissue's Importance: Connective tissue is crucial for holding the body together and maintaining its structure.
2. Flo Hyman's Story: Hyman’s death from Marfan Syndrome illustrates how connective tissue disorders can have fatal consequences.
3. Marfan Syndrome: A genetic disorder affecting connective tissue, causing it to weaken over time, leading to problems in joints, eyes, lungs, and the heart.
4. Connective Tissue Types: The four main types of connective tissue are proper connective tissue, cartilage, bone, and blood.
5. Proper Connective Tissue: Found in ligaments, skin, and fat, this type of tissue plays various roles, including storage, insulation, and structural support.
6. Bone and Cartilage: Both are types of connective tissue that provide structural support to the body.
7. Blood as Connective Tissue: Blood is considered connective tissue because it transports nutrients, hormones, and other materials throughout the body.
8. Connective Tissue Composition: It is composed primarily of the extracellular matrix, which contains ground substance and fibers.
9. Ground Substance: A watery, flexible material in the extracellular matrix that cushions and protects cells.
10. Connective Tissue Fibers: Collagen, elastic, and reticular fibers provide strength, flexibility, and support.
11. Collagen Fibers: Strong, tough fibers that support tissues and resist stretching.
12. Elastic Fibers: Allow tissues to stretch and return to their original shape, found in skin, lungs, and blood vessels.
13. Reticular Fibers: Delicate fibers that form a supportive framework around organs.
14. Blast Cells: Immature cells that produce the matrix in connective tissue, such as chondroblasts (cartilage) and osteoblasts (bone).
15. Cyte Cells: Mature cells that maintain the extracellular matrix and can revert to blast cells if necessary.
16. Mesenchyme: The common origin of all connective tissues, composed of loose, mobile embryonic cells.
17. Immune Cells in Connective Tissue: Macrophages and white blood cells (leukocytes) protect the body from pathogens and dead cells.
18. Avascular Connective Tissue: Some connective tissues, like cartilage, lack blood vessels and rely on surrounding tissues for nutrients.
19. Marfan Syndrome's Impact: The disorder weakens elastic fibers, particularly in the aorta, leading to severe cardiovascular complications.
20. Role of Connective Tissue in Everyday Function: From storing fat to protecting organs and transporting blood, connective tissue is essential for bodily functions.
20 Key Points
1. Connective Tissue Diversity: Found throughout the body in various forms, including bone, blood, and fat.
2. Extracellular Matrix: The primary component of connective tissue, made of ground substance and fibers.
3. Ground Substance Function: Protects cells by creating a flexible, supportive environment.
4. Collagen Strength: Collagen fibers provide strength and flexibility, making them crucial for skin and tissues.
5. Elasticity in Tissues: Elastic fibers allow tissues like skin to stretch and return to their shape.
6. Marfan Syndrome's Effects: A genetic mutation weakens connective tissue, leading to life-threatening conditions.
7. Blast and Cyte Cells: Immature blast cells build the extracellular matrix, while mature cyte cells maintain it.
8. Immune Protection: Macrophages and leukocytes in connective tissue help fight infections and remove dead cells.
9. Connective Tissue's Vital Roles: Provides structural support, facilitates movement, and stores energy.
10. Bone Formation: Osteoblasts create bone by laying down a matrix that hardens with calcium.
11. Cartilage Formation: Chondroblasts form cartilage, a flexible tissue found in joints and the nose.
12. Blood as a Connective Tissue: Transports vital substances like oxygen and hormones throughout the body.
13. Fat's Role: Connective tissue that insulates, stores energy, and supports organs.
14. Elastic Fibers in the Aorta: Marfan Syndrome affects elastic fibers in the aorta, making it prone to enlargement and rupture.
15. Connective Tissue's Origin: All connective tissues develop from mesenchyme.
16. Avascular Cartilage: Cartilage lacks blood vessels and relies on nearby tissues for nutrient delivery.
17. Collagen Injections: Collagen is sometimes injected into the skin to reduce signs of aging.
18. Mesenchymal Cells: The embryonic cells that give rise to connective tissues can move and adapt.
19. Proteoglycans: Proteins in the ground substance that help retain water and provide tissue flexibility.
20. Marfan Syndrome and Heart: The weakening of connective tissue in the heart and blood vessels can lead to fatal consequences, such as aortic dissection.
20 Important Medical Terms and Explanation
1. Marfan Syndrome: A genetic disorder that affects connective tissue, causing it to weaken and leading to severe complications.
2. Connective Tissue: Tissue that supports, binds, and protects the body’s organs and other tissues.
3. Proper Connective Tissue: A type of connective tissue that includes ligaments, skin, and fat.
4. Cartilage: A flexible connective tissue that provides cushioning in joints and forms structures like the nose and ears.
5. Bone: A type of connective tissue that provides structural support and protects organs.
6. Blood: A type of connective tissue that circulates nutrients, hormones, and oxygen throughout the body.
7. Extracellular Matrix: The nonliving material between connective tissue cells, made of ground substance and fibers.
8. Ground Substance: The watery, unstructured part of the extracellular matrix that cushions cells.
9. Collagen Fibers: Strong, flexible fibers in connective tissue that provide support and structure.
10. Elastic Fibers: Flexible fibers that allow tissues to stretch and return to their original shape.
11. Reticular Fibers: Delicate fibers that form networks to support soft organs like the liver and spleen.
12. Blast Cells: Immature connective tissue cells that produce the extracellular matrix.
13. Cyte Cells: Mature cells that maintain the extracellular matrix.
14. Mesenchyme: The embryonic tissue from which all connective tissue develops.
15. Avascular: Lacking blood vessels, as seen in some types of connective tissue like cartilage.
16. Osteoblasts: Immature bone cells that produce bone matrix.
17. Chondroblasts: Immature cartilage cells that produce the cartilage matrix.
18. Macrophages: Immune cells in connective tissue that ingest foreign materials and dead cells.
19. Leukocytes (White Blood Cells): Immune cells in the blood that protect the body from infection.
20. Proteoglycans: Protein molecules in the ground substance that help trap water and provide tissue resilience.
20 Quotes
1. "Flo Hyman had always been a tall girl... by 17 she’d topped out at just over 6’5’’."
2. "Hyman’s initial cause of death was thought to be a heart attack, but an autopsy revealed that she died from a tear in her aorta."
3. "Marfan Syndrome is a genetic disorder of the connective tissue."
4. "People suffering from it have a defect in their connective tissue that substantially weakens it over time."
5. "Marfan’s tend to be especially tall and thin, like Flo Hyman, with loose, flexible joints and noticeably longer limbs and fingers."
6. "All connective tissues have three factors in common that set them apart from other tissue types."
7. "They all develop from mesenchyme, a loose and fluid type of embryonic tissue."
8. "Connective tissues have different degrees of vascularity, or blood flow."
9. "All connective tissues are mostly composed of nonliving material, called the extracellular matrix."
10. "Collagen is by far the strongest and most abundant type of fiber."
11. "Elastic fibers allow them to stretch and recoil like rubber bands."
12. "Reticular fibers form delicate, sponge-like networks that cradle and support your organs."
13. "Blast cells... are the stem cells that are still in the process of dividing to replicate themselves."
14. "Chondroblasts are the blast cells of cartilage."
15. "Osteoblasts are the blast cells of bone tissue."
16. "Macrophages patrol your connective tissues and eat bacteria, foreign materials, and even your own dead cells."
17. "White blood cells, or leukocytes... scour your circulatory system fighting off infection."
18. "In the case of your connective tissue, Marfan Syndrome affects those fibers... causing weakness in the matrix."
19. "The aorta begins to enlarge -- so much so that it can rupture."
20. "So much going on with your connective tissue... we’re going to spend one last lesson on them next week."
Transcript
Flo Hyman had always been a tall girl.
I mean... really tall.
By her 12th birthday, she was already six feet, and by 17, she’d topped out at just over 6’5”.
Initially self-conscious about her stature, she learned to use it to her advantage when she started playing volleyball.
She attended the University of Houston as the school’s first female scholarship athlete, and at the age of 21, she was competing in World Championships. Nine years later, she made it to the 1984 Olympics and helped her team win the silver medal.
After the Olympics, Hyman moved to Japan, where she gained fame playing professional volleyball.
But all of that ended in 1986 when, out of nowhere, she collapsed and died during a game.
She was 31 years old.
Hyman’s initial cause of death was thought to be a heart attack, but an autopsy revealed that she died from a tear in her aorta, caused by an undiagnosed condition known as Marfan Syndrome.
Marfan Syndrome is a genetic disorder of the connective tissue. People suffering from it have a defect in their connective tissue that substantially weakens it over time.
And you’ve got connective tissue pretty much everywhere in your body, so it can cause big problems.
Outwardly, those with Marfan’s tend to be especially tall and thin, like Flo Hyman, with loose, flexible joints and noticeably longer limbs and fingers.
Those long fingers and bendy joints have actually helped some athletes and musicians do things that the rest of us can’t. Famous blues guitarist Robert Johnson, piano virtuoso Sergei Rachmaninov, and Italian violinist Niccolò Paganini are all believed to have had Marfan Syndrome.
But these abilities come at a great cost. As people with Marfan’s get older, their weakening tissue can cause serious problems in the joints, eyes, lungs, and heart.
The fact that a single genetic mutation can affect your bones, cartilage, tendons, blood vessel walls, and more shows that all of those structures are closely related, no matter how different they may seem.
We’ve covered the basic properties of nervous, muscle, and epithelial tissue, but we haven’t gotten to the most abundant and diverse of the four tissue types — our connective tissue.
This is the stuff that keeps you looking young, makes up your skeleton, and delivers oxygen and nutrients throughout your body. It’s what holds you together, in more ways than one.
And if something goes wrong with it, you’re in for some havoc.
And that means we’re gonna be talkin’ about Jello today.
Uh... we’ll get to that in a minute.
The springiness here? That’s connective tissue. So is the structure in here, and the stuff inside here, and the tendons popping out here.
Connective tissue is pretty much everywhere in your body, although how much of it shows up where varies from organ to organ. For instance, your skin is mostly connective tissue, while your brain has very little, since it’s almost all nervous tissue.
You’ve got four main classes of connective tissue — proper, or the kind you’d find in your ligaments and supporting your skin, along with cartilage, bone, and blood.
Whaaaa?
Sounds a little weird, but your bones and your blood are just types of connective tissue!
So, despite the name, your connective tissues do way more than just connect your muscles to your bones.
Your fat — which is a type of proper connective tissue — provides insulation and fuel storage, whether you like it or not, but it also serves structural purposes, like holding your kidneys in place and keeping your eyeballs from popping out of your skull.
Your bones, tendons, and cartilage bind, support, and protect your organs, and give you a skeleton so that you can move with a purpose instead of blobbing around like an amoeba.
And your blood transports your hormones, nutrients, and other material all over your body. There’s no other substance in you that can boast this kind of diversity.
But if they’re so different, how do we know that anything is a connective tissue? Well, all connective tissues have three factors in common that set them apart from other tissue types.
First, they share a common origin: They all develop from mesenchyme, a loose and fluid type of embryonic tissue. Unlike the cells that go on to form, say, your epithelium, which are fixed and neatly arranged in sheets, mesenchymal cells can be situated any-which-way and can move from place to place.
Connective tissues also have different degrees of vascularity, or blood flow. Most cartilage is avascular, for example, meaning it has no blood vessels, while other types of connective tissue, like the dense irregular tissue in your skin, are brimming with blood vessels.
Finally — and as strange as it may sound — all connective tissues are mostly composed of nonliving material, called the extracellular matrix. While other tissue types are mainly made of living cells packed together, the inert matrix between connective-tissue cells is actually more important than what’s inside the cells.
Basically, your connective tissue, when you see it up close, looks and acts a lot like this.
Yeah. The most abundant and diverse tissue in your body, that makes all of your movements and functions possible? Turns out it’s not that different from the dessert that Aunt Frances brings to every holiday party.
The jello that gives this confection its structure is like that extracellular matrix in your connective tissue. The actual cells are just intermittent little goodies floating around inside the matrix, like the little marshmallows.
And although it may not look like it in this particular edible model, the extracellular matrix is mostly made of two components. The main part is the ground substance — a watery, rubbery, unstructured material that fills in the spaces between cells and, like the gelatin in this dessert, protects the delicate, delicious cells from their surroundings.
The ground substance is flexible because it’s mostly made of big ol’ starch and protein molecules mixed with water.
The anchors of this framework are proteins called proteoglycans. And from each one sprouts lots and lots of long, starchy strands called glycosaminoglycans, or GAGs, radiating out from those proteins like brush bristles.
These molecules then clump together to form big tangles that trap water, and if you’ve ever made glue out of flour, you know that starch, protein, and water can make a strong and gooey glue.
But running throughout the ground substance is another important component: fibers, which provide support and structure to the otherwise shapeless ground substance. And here, too, are lots of different types.
Collagen is by far the strongest and most abundant type of fiber. Tough and flexible, it’s essentially a strand of protein, and stress tests show that it’s actually stronger than a steel fiber of the same size. It’s part of what makes your skin look young and plump, which is why sometimes we inject it into our faces.
In addition, you’ve also got elastic fibers — which are longer and thinner and form a branching framework within the matrix. They’re made out of the protein elastin, which allows them to stretch and recoil like rubber bands; they’re found in places like your skin, lungs, and blood vessel walls.
Finally, there are reticular fibers — short, finer collagen fibers with an extra coating of glycoprotein. These fibers form delicate, sponge-like networks that cradle and support your organs like fuzzy nets.
So, there’s ground substance and fibers in all connective tissue, but let’s not forget about the cells themselves.
With a tissue as diverse as this, naturally, there are all kinds of connective tissue cells, each with its unique and vital task — from building bone to storing energy to keeping you from bleeding to death every time you get a paper cut.
But each of these signature cell types manifests itself in two different phases: immature and mature. You can recognize the immature cells by the suffix they all share in their names: -blast.
“Blast” sounds kinda destructive, but literally, it means “forming” — these are the stem cells that are still in the process of dividing to replicate themselves. But each kind of blast cell has a specialized function, namely, to secrete the ground substances and fibers that form its unique matrix.
So, chondroblasts, for example, are the blast cells of cartilage. When they build their matrix around them, they’re making the spongy tissue that forms your nose and ears and cushions your joints.
Likewise, osteoblasts are the blast cells of bone tissue, and the matrix they lay down is the nexus of calcium carbonate that forms your bone. Once they’re done forming their matrix, these blast cells transition into a less active, mature phase. At that point, they trade in -blast for the suffix -cyte. So, an osteoblast in your bone becomes an osteocyte — ditto for chondroblasts becoming chondrocytes.
These cyte cells maintain the health of the matrix built by the blasts, but they can sometimes revert back to their blast state if they need to repair or generate a new matrix.
So, the matrices that these cells create are pretty much what build you — they assemble your bone and your cartilage and your tendons and everything that holds the rest together.
Not bad for a bunch of marshmallows floating in jello.
BUT! There is another class of connective tissue cells that are responsible for an equally important role. And that is: protecting you from pretty much everything.
These are cells that carry out many of your body’s immune functions.
I’m talking about macrophages, the big, hungry guard cells that patrol your connective tissues and eat bacteria, foreign materials, and even your own dead cells.
And your white blood cells, or leukocytes, that scour your circulatory system fighting off infection? They’re connective tissue cells, too.
Because this matrix-based tissue system is everywhere in your body — from your skin to your fat to your blood to your bones — your connective tissue is your first line of defense, no matter where in your body trouble arises.
But when it comes to connective tissue, not all trouble can be fixed.