Connective Tissue Fibers Histology [Connective Tissue Histology Part 1 of 3]

Summary

This video from the Da Vinci Academy's histology course on YouTube delves into connective tissue, a fundamental topic in histology. It explains the composition of extracellular matrix and cells, highlighting the predominance of supportive fibers like collagen and elastin over cellular components. The lecture differentiates connective tissue from epithelial tissue, introduces the concept of parenchyma and stroma, and discusses the embryonic origin of connective tissue. It also covers the structure and function of collagen types, the synthesis process of collagen and elastin, and the importance of these proteins in providing strength and elasticity to various tissues.

Takeaways

• 📚 The Da Vinci Academy's histology video course is available on YouTube, covering fundamental principles of histology and relevant cell biology.
• 🔍 The course includes a histology playlist and additional resources such as practice questions and lab videos accessible through their website.
• 🌟 Connective tissue is one of the four main tissue types and includes various tissues like cartilage, bone, adipose tissue, and specialized connective tissues.
• 🧬 Connective tissue is characterized by a higher proportion of extracellular matrix compared to cells, with supportive fibers like collagen and elastin being predominant.
• 🏠 The main function of connective tissue is to support and protect the functional tissue of organs, distinguishing it from parenchyma, which refers to the functional tissue itself.
• 🔵 Connective tissue elements mostly originate from mesenchyme, the embryonic connective tissue, and the mesoderm germ layer.
• 🌈 Extracellular matrix is composed of extracellular fibers, ground substance, and fluids, including collagen, reticular fibers, elastic fibers, glycoproteins, proteoglycans, and glycosaminoglycans.
• 🔑 Fibroblasts are the primary cells found in connective tissue proper, with other cells like adipocytes, white blood cells, and mast cells also present.
• 💪 Collagen is the most abundant protein in the human body and provides significant tensile strength with limited flexibility, essential for the supportive role of connective tissue.
• 🔍 There are four major types of collagen (Type 1, 2, 3, and 4), each with specific locations and functions in the body, important for understanding tissue structure and wound repair.
• 🎈 Elastin is a highly elastic protein allowing tissues to stretch and return to their original shape, crucial for the function of tissues in organs like the lungs and aorta.

Q & A

What is the main focus of the first lecture in the Connective Tissue Proper series?

The first lecture in the Connective Tissue Proper series focuses on defining what connective tissue is, the fibers that comprise it, and distinguishing it from other basic tissue types.

What are the four main tissue types discussed in the video course?

The four main tissue types discussed in the video course are epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

What is the primary component of connective tissue?

The primary component of connective tissue is the extracellular matrix, which includes supportive fibers like collagen and elastin, rather than cells.

What is the main function of connective tissue in the body?

The main function of connective tissue is to support and protect the functional tissue of organs.

What is the difference between parenchyma and stroma in the context of an organ?

Parenchyma refers to the functional tissue of an organ, while stroma is the supportive connective tissue that surrounds and supports the parenchyma.

Which tissue type do most connective tissue elements originate from?

Most connective tissue elements originate from mesenchyme, which is embryonic connective tissue.

What are the main components of the extracellular matrix in connective tissue?

The main components of the extracellular matrix in connective tissue are extracellular fibers, ground substance, and fluids, including collagen, reticular fibers, elastic fibers, glycoproteins, proteoglycans, and glycosaminoglycans.

What is the most prominent structural protein found in the extracellular matrix, and what is its role?

The most prominent structural protein in the extracellular matrix is collagen, which provides significant tensile strength with limited flexibility, making it ideal for supportive roles in various tissues throughout the body.

What are the four major types of collagen fibers, and what are their primary locations and functions?

The four major types of collagen fibers are Type 1, Type 2, Type 3, and Type 4. Type 1 is found in bone, tendon, dentin, fascia, and cornea, providing strength. Type 2 is found in cartilage, the vitreous body, and intervertebral discs. Type 3, also known as reticular fibers, is found in the dermis, blood vessels, lymph nodes, and fetal tissue. Type 4 forms flexible fibrous sheets in the basal lamina and basement membrane.

What is the process of collagen synthesis, and how does it differ from elastin synthesis?

Collagen synthesis involves the formation of procollagen within the cell, which is then exported and undergoes further modification to form cross-linked collagen fibers. Elastin synthesis is similar, with tropoelastin being synthesized and secreted, then cross-linking to form elastin. The main difference lies in the specific proteins and the structure of the final fibers they form.

What is the role of elastin in the body, and where is it primarily found?

Elastin is a highly elastic protein that allows tissues to stretch and return to their original shape. It is primarily found in tissues that require elasticity, such as lung tissue, the aorta, large blood vessels, ligaments, vocal cords, and the bladder.

Outlines

00:00

🌟 Introduction to Connective Tissue in Histology

The script begins with an introduction to the da Vinci Academy's histology video course, available on YouTube, which covers the fundamental principles of histology and relevant cell biology. The course includes lectures on connective tissue, one of the four main tissue types, with a focus on connective tissue proper, its composition of extracellular matrix and cells, and its supportive role in organs. The lecture differentiates between parenchyma, the functional tissue of an organ, and stroma, the supportive connective tissue. It also touches on the origin of connective tissue from mesenchyme and its relation to the mesoderm germ layer.

05:01

🚩 The Structure and Function of Collagen in Connective Tissue

This paragraph delves into the specifics of collagen, the most abundant protein in the human body and a key component of connective tissue. It discusses the tensile strength and limited flexibility of collagen, which make it ideal for support. Four major types of collagen are identified: type 1, found in bone, tendon, and other strong tissues; type 2, in cartilage and the vitreous body of the eye; type 3, known as reticular fibers in skin and other areas, and involved in early wound repair; and type 4, forming flexible sheets in the basal lamina and basement membrane. The paragraph also explains the process of collagen synthesis, from procollagen to tropocollagen, and the role of vitamin C in hydroxylation, a necessary step for collagen's triple helix structure.

10:03

🧬 Elastin and Elastic Fibers: Properties and Synthesis

The script continues with an exploration of elastin, a highly elastic protein that allows tissues to stretch and return to their original shape, essential for the function of structures like the lungs and aorta. Elastin is found in large blood vessels, ligaments, and the bladder. The synthesis of elastin is described as similar to that of collagen, involving fibroblasts and enzymes like lysyl oxidase, which facilitates cross-linking between tropoelastin molecules to form elastin. The breakdown of elastin by elastase and its inhibition by alpha-1 antitrypsin is also mentioned, hinting at clinical implications.

15:03

🌌 The Composition and Role of Elastic Fibers in Tissue Function

This section describes the composition of elastic fibers, which include both elastin and microfibrillar scaffolding, primarily made of fibrillin. The process of creating an elastic fiber involves the aggregation of cross-linked tropoelastins onto the microfibrillar scaffold, further cross-linking to form the complete elastic fiber. The importance of these fibers in tissues that undergo dynamic stretching, such as arteries, is emphasized, showcasing their role in the elasticity and function of these structures.

20:05

📚 Conclusion and Resource Access for Histology Course

The final paragraph concludes the video with a reminder that the da Vinci Academy histology video course is available on YouTube and encourages viewers to access corresponding practice questions and histology lab videos through the provided website link in the video description. It serves as a call to action for further learning and engagement with the course materials.

Keywords

💡Connective Tissue

Connective tissue is a broad term that encompasses various types of tissues, including but not limited to cartilage, bone, adipose tissue, and specialized connective tissues. It is characterized by a high proportion of extracellular matrix compared to cells, serving supportive and protective functions for organs. In the video, connective tissue is the main focus, with an emphasis on its composition and role in the body, as well as the different types of fibers that comprise it.

💡Extracellular Matrix

The extracellular matrix is a complex network of fibers, ground substance, and fluids that provide structural and functional support to the surrounding cells within connective tissues. It is a key component of connective tissue, as mentioned in the script, where it forms the major part of the tissue, with cells being less abundant. The extracellular matrix includes collagen, elastin, and other proteins that contribute to the tissue's properties.

💡Fibers

Fibers in the context of the video refer to the supportive protein structures within the extracellular matrix of connective tissues. These fibers, such as collagen and elastin, provide strength, elasticity, and resilience to the tissues. The script discusses the different types of fibers, their locations, and functions, highlighting their importance in the structure and support of various organs.

💡Collagen

Collagen is the most abundant protein in the human body and a key structural component of the extracellular matrix. It provides significant tensile strength with limited flexibility, making it essential for supportive connective tissues throughout the body. The video script describes collagen's role in wound repair and the different types of collagen, such as type 1 found in bone and tendons, and type 2 found in cartilage.

💡Elastin

Elastin is a highly elastic protein that allows tissues to stretch and return to their original shape. It is crucial for the function of tissues that undergo frequent stretching, such as lung tissue and large blood vessels. The script explains the structure and synthesis of elastin, as well as its role in the elasticity of tissues and its contribution to the function of the aorta and other elastic arteries.

💡Epithelial Tissue

Epithelial tissue is one of the four main tissue types, distinct from connective tissue. It is composed mainly of epithelial cells with a smaller amount of extracellular matrix. In the script, epithelial tissue is mentioned in contrast to connective tissue, emphasizing the difference in the proportion of cells to extracellular matrix and their respective functions.

💡Mesenchyme

Mesenchyme is the embryonic connective tissue from which most connective tissue elements originate. It is a significant concept in the script as it relates to the developmental origins of connective tissues and their role in the formation of various structures in the body.

💡Germ Layers

The germ layers are the three primary layers of cells that form during embryonic development: the ectoderm, mesoderm, and endoderm. The script mentions the mesoderm as the germ layer that gives rise to connective tissues, among other tissue types, highlighting the developmental importance of this layer in the formation of the body's structures.

💡Fibroblasts

Fibroblasts are the primary cells found in connective tissue proper. They are responsible for the synthesis of the extracellular matrix, including collagen and elastin. The script describes fibroblasts as a key cellular component of connective tissue, essential for its structural integrity and function.

💡Wound Repair

Wound repair is a biological process that involves the healing of damaged tissues. The script provides an overview of the stages of wound repair, emphasizing the role of collagen in the formation of scar tissue. It explains the transition from collagen type 3, which forms the initial scaffolding, to collagen type 1, which provides the strength needed for a robust scar.

💡Loose Connective Tissue

Loose connective tissue is a type of connective tissue characterized by a more open arrangement of fibers and cells, allowing for greater flexibility. The script uses this term to describe a specific type of connective tissue where cells are more dispersed among the fibers, providing an example of the tissue's composition and structure.

Highlights

The Da Vinci Academy's histology video course is available on YouTube, covering fundamental principles of histology and relevant cell biology.

The course includes a histology playlist and access to practice questions and lab videos through the academy's website.

Connective tissue is one of the four main tissue types, consisting of extracellular matrix and cells, with a higher proportion of matrix.

Connective tissue's primary function is to support and protect the functional tissue of organs.

Parenchyma refers to the functional tissue of any organ, while stroma is the supportive tissue.

Most connective tissue elements originate from mesenchyme, the embryonic connective tissue.

Extracellular matrix is composed of extracellular fibers, ground substance, and fluids, including collagen, reticular fibers, elastic fibers, glycoproteins, proteoglycans, and glycosaminoglycans.

Fibroblasts are the main cells found in connective tissue proper, with other cells like adipocytes, white blood cells, and mast cells also present.

Loose connective tissue is characterized by a significant presence of fibers and ground substance with fewer cells.

Collagen is the most prominent and abundant protein in the extracellular matrix, providing significant tensile strength.

There are four major types of collagen: Type 1, Type 2, Type 3, and Type 4, each with specific locations and functions in the body.

Collagen type 1 is produced during the late phases of wound repair to form fibrous scar tissue.

Elastin is a highly elastic protein allowing tissues to stretch and resume their native shape, found in structures like the lung and aorta.

Elastic fibers contribute to the function of tissues by allowing expansion and recoil, as seen in the aorta during cardiac cycles.

Elastin synthesis involves the formation of tropoelastin, which is cross-linked to form elastic fibers with the help of enzymes like lysyl oxidase.

Fibrillin is a glycoprotein that forms the microfiber scaffold for the deposition of elastin in elastic fibers.

Transcripts

welcome to the da vinci academy

histology video course

the entire video course is available on

youtube and covers all of the

fundamental principles of histology and

relevant cell biology you can find all

the videos from the course by clicking

the histology playlist link in the

description below

and then you can access the

corresponding practice questions and

histology lab videos by going to our

website which is also linked in the

description below

so this is the first of three lectures

covering connective tissue proper which

is actually one of the four main tissue

types that we're going to go over in

this first unit and in this first

lecture here for connective tissue we're

going to talk about what is connective

tissue and then the fibers that comprise

connective tissue

and the four basic tissue types again so

dr lee talked to you about epithelial

tissue this lecture we're going to talk

about connective tissue which is a broad

term that includes a number of different

tissues so obviously connective tissue

proper

connective tissue also includes

cartilage

it includes bone

adipose tissue

and several other types of specialized

connective tissues as well so in this

lecture we're mainly going to focus on

connective tissue proper because we have

other separate lectures exclusively

dedicated to these other types of

specialized connective tissue

so what is connective tissue it consists

of extracellular matrix and cells and

what's important to remember about

connective tissue is that there's a much

higher proportion of the extracellular

matrix than there are cells certainly

they're cells floating around but the

major component of connective tissue are

these supportive fibers like collagen

elastin

fibers like that versus in the

epithelium remember that if this was

reversed the major component of

epithelium is the epithelial cells and

then you do have some extracellular

matrix components to support those cells

the main function of connective tissue

is to support and protect the functional

tissue of organs this is a great segue

into explaining the difference between

parenchyma and stroma so if we look at

the submandibular gland here this is a

zoomed out view here and if you look at

it the parenchyma is very easily defined

and so this is the glandular tissue here

and you can see it here again

and then if you zoomed in here again on

this on this portion here

you can see it's very easily defined if

you look on the outskirts here here's

this eosinophilic fibers like this kind

of surrounding it separating these

different functional units this is

what's called the stroma so again this

is the parenchyma

which is a general term that just refers

to the functional tissue of any organ

and then you have it here so this is

connective tissue here

and you can see out here here's the you

know it's again stains very eosinophilic

a lot of proteins extracellular matrix

you can see some blood vessels in here

you see some adipose tissue in here

found right here and this is what's

called the stroma

which is the supportive tissue of the

organ so it supports the parenchyma

most connective tissue elements

originate from the mesenchyme which is

essentially embryonic connective tissue

and then as far as the germ layers go

you remember you have the mesoderm

and the mesoderm gives rise to some

connective tissue but it also can give

rise to epithelial and muscle tissues as

well so the connective tissue components

again we said extracellular matrix and

cells extracellular matrix is made of

extracellular fibers ground substance

and fluids specifically it has collagen

reticular fibers elastic fibers

glycoproteins proteoglycans and

glycoaminoglycans

or gags and we'll talk about each of

these individually over the next few

slides cells main cell you're going to

find in connective tissue proper

especially as fibroblasts you can also

see adipocytes in adipose tissue you'll

see white blood cells floating around to

contributing to immune function and you

can also see mast cells as well and so

if you look at this this is a great

example of what's called loose

connective tissue and we'll explain more

in detail what that means in a over the

course of the lecture but just to give

you a sense here you can see there are

some cells in here here's a mast cell

here here's some other cells floating

around in here and but you'll notice

that it's not mainly composed of cells

there's a lot of other fibers here so

this would be an elastic fiber here

you can see these red squiggly lines

like this these are what i would call

collagen fibers because remember again

proteins often will stain eosinophilic

and so you see a lot of different fibers

then you kind of see this what's called

ground substance which is this

gelatinous like substance and it's

almost like a soup if you will it's it's

a you know you have the ground substance

you have some fluid in there some water

component to it you have a lot of these

fibers floating around and then kind of

the component of the soup if you if you

will you have you know these cells

floating around within it

so the most prominent structural protein

of the extracellular matrix is collagen

and it's also the most abundant protein

in the human body which isn't too

surprising because you have supportive

connective tissue all throughout your

body in literally almost every organ and

the reason for that is that collagen

provides significant tensile strength

with limited flexibility so it's a great

supportive fiber and there's four major

types that you need to be familiar with

there's type 1 type 2 type 3 and type 4.

and so these are just some images we'll

revisit these again throughout the

lecture but just to kind of point out

some collagen fibers kind of in black

here these would be supportive collagen

fibers within the lymph node these are

also known as reticular fibers talk

about what that means in a second here

then if you look at this slide from

skeletal muscle so this is the skeletal

muscle tissue down here and kind of this

purplish reddish color here and then

here

these bright red fibers here these are

collagen fibers and so you can see where

they stain very brightly red usually

so the different types this is just kind

of a table to help you figure out the

location and the function it's really

important to know both the location and

the function for each of these these are

very commonly test questions so you have

collagen type 1

so type 1 is is

very strong it's able to

sustain a large amount of force

therefore it's found in bone it's

actually synthesized by osteoblasts

within the bone but it can also be found

in a tendon dentin

fascia and then the cornea within the

eye and what's important to know with

collagen is that you have the collagen

protein

which then forms collagen fibrils by

cross-linking the proteins

and then those merge together to form

collagen fibers

and we'll go over this when we talk

about collagen synthesis in a few slides

here

the other thing is that what that's

important to know that's very high yield

for exams especially a board exam is

that collagen type 1 is produced during

the late phases of wound repair to form

a fibrous scar tissue so just a very

brief overview of wound repair so if you

have a wound like this kind of a break

in the skin

the first thing you're going to do is

you know you're obviously going to be

bleeding so the body's going to achieve

hemostasis by forming a clot in here

then you're going to have you're going

to have cellular debris because it's

essentially damaged so you got to have

these immune cells come in

essentially clean things up the cleanup

crew

then next what you're going to do is

you're actually going to lay this kind

of structural framework or this

scaffolding and these are actually

collagen type 3 fibers or reticular

fibers

and they kind of serve as the framework

for then later stages where you actually

form the fibrous scar tissue by laying

in

your collagen type 1 fibers and that

makes sense collagen type 1 is much

stronger it's going to give you a much

better scar much stronger scar tissue

here to help fully seal this wound so

you go from collagen type 3 to collagen

type 1. again very commonly a test

question on the boards

type 2 collagen is found in cartilage

and in the vitreous body in the eye it's

also found in intervertebral discs

specifically if you remember a disc

structure it's kind of like a jelly

filled donut

you have this kind of gel in the middle

here and then you have this outer

surface here this much tougher

kind of structural surface here and this

inner portion is called the nucleus

pulposus this is composed of type 2

fibers along with within this gelatinous

mix in here then you have the annulus

fibrosis which is this much more tensile

much stronger

covering around around the gel and this

is composed of both type 1 and type 2

fibers

type 3 as we say here with the star is

also called reticular fibers and these

again they kind of cross link like this

these fibers will come together and

they'll cross link like this to kind of

form a scaffold or a mesh structure and

they form in a lot of different areas

the skin mainly the dermis blood vessels

lymph nodes the uterus and fetal tissue

as well they're also as we said produced

during the early phase of wound repair

to produce what's called granulation

tissue so that framework that's laid

down first it's called granulation

tissue composed of type 3 and then you

form on top of that the fibrous scar

tissue which is composed of type 1.

then lastly here type 4 this forms

flexible fibrous sheets found in the

basal lamina and the basement membrane

so again if you have

your epithelial layer like this

and so you have your lumen out here

where absorption is occurring or

secretion

and then you're going to have this basal

laminar basement membrane where all

these cells are adherent to and this is

mainly composed of collagen type 4.

these are just some histological

examples so this is from the bone this

is type 1 so you can see that in here

very compact structure this is type 2

which is cartilage

type 3 again this is from a lymph node

these are those reticular fibers you can

kind of see them here in black

and then type 4 here this can be

difficult to see it's really what you're

just kind of looking for is this line

here

that's you know forming uniformly below

this epithelial layer which is where you

would see collagen type 4.

so collagen structure

is a pro alpha chain which is composed

of the following sequence glycine plus

two more amino acid residues and those

are either proline or lysine

so it would be it could be something

like this where you have proline

like this and then it repeats again like

this and it could be the reverse

like that and then so on and so on and

so as you can see

a good portion actually a third of

collagen is glycine

and then

this sequence is modified in the cell to

form a triple helix composed of three

pro alpha chains

so you have three

right here three alpha chains which then

form a triple helix and you can see this

whole structure here is a triple helix

so pro collagen triple helix which would

be this structure here is actually

exported outside of the cell

where it undergoes further modification

to enable cross linking between these

triple helices so you can see here's one

here here's another one here you can see

these cross links being formed here

and so the final collagen fiber is

actually a structure with multiple

crosslink collagen triple helices and

you can see that here so here's triple

helis is here

cross-linked here cross-linked here it's

synthesized by fibroblasts which are

cells found in connective tissue so

really the outline is you have the

pre-pro collagen

which is synthesized in within the cell

within the rough er actually

specifically then you have the pro

collagen which is formed after some

modifications to the initial sequence

that's exported out and then you have

tropo collagen which is here

and then these

undergo that cross-linking to form

collagen fibers so first there's an air

in this figure this is not the cytosol

this is the

extracellular space

this is the cytosol here

and actually a good portion of this

actually takes place

within the rough er

or the rough endoplasmic reticulum and

what that enables is actually exocytosis

of pro-collagen which would be this last

portion here to the extracellular space

here and then that's where synthesis is

completed so first prepro collagen is

translated from collagen mrna in the

rough er to produce the pro alpha chain

which is that glycine

plus xy and remember one of these is

either a proline or a lysine

and so this is here just like any how

any other protein is formed is first

it's translated from the mrna so you

have this initial sequence here and then

the proline and lysines undergo

hydroxylation in the rough er and this

is actually a process that requires

vitamin c

then after hydroxylation

they undergo glycosylation as you can

see here and here and what these

processes specifically hydroxylation do

is they enable the helical alpha chains

to spontaneously form a triple helix in

the rough er and you can see that here

and this is what's called

pro collagen and this occurs via

hydrogen and disulfide bonds to help

form this triple helis helix structure

here then this pro collagen is exported

via exocytosis to the extracellular

space where it undergoes the final steps

in collagen synthesis so outside the

cell

again

the terminal disulfide rich pro peptides

of the pro-collagen so this is

pro-collagen here

are cleaved by peptidases to form

tropical collagen so you have cleavage

here and you can see these little ends

coming off here

then you form

one of these triple helices with the c

and n termini

cleaved off and this is

tropol collagen

then you have an enzyme called lysol

oxidase which catalyzes the oxidation of

lysine side chains of tropical collagen

to yield reactive aldehydes then these

reactive aldehydes form covalent lysine

hydroxy lysine crosslinks and that's

shown here

between these tropical collagen

molecules and this allows for

spontaneous formation of the cross

linking between the tropo collagen so

here's a tropical collagen cross-linking

here and here to this one and then it's

cross-linking to this one as well and so

what ends up happening is that you have

multiple tropo collagen fibers that are

cross-linked together

to form the

collagen fiber

cross-linking between tropo collagen

chains within collagen fibers actually

continues to occur so you continue to

get more of these crosslinks

throughout life

and it leads to increased stiffness of

structures that contain collagen with

age

particularly skin joints and arteries

and this is what leads to some of the

detriments of older age so over the next

few slides we'll talk about elastin and

elastic fibers so elastin is a highly

elastic protein that allows tissues to

be stretched and resume their native

shape so you have some kind of

deformity on this

or some stretch and shape and then it

resumes back to the native shape and

this elastic nature often contributes to

the function of tissue that actually

contains elastic fibers so lung tissue

for example contains a lot of elastic

fibers because the elastic fibers allow

the lung tissue to expand on inspiration

and then the recoil of the elastic

fibers allows to push it for air out

during expiration and then the aorta

also contains

numerous elastic fibers because that's

also contributing to its

function as well so if we look at the

aorta during systolic ejection

ventricular ejection it expands in all

directions and its elastic fibers allow

it to do that so it's able to expand and

accommodate a higher volume of blood and

then when ejection ends

you have this diastolic recoil which

then gives you kind of an extra pulse of

blood or the diastolic pulse of blood

and that contributes to your diastolic

blood pressure elastic fibers are also

found in large blood vessels other than

the aorta such as the veins the vena

cava it's also found in elastic

ligaments vocal cords

ligamentum flavum which is a ligament in

the spine and then the bladder as well

so a lot of structures here that you

know have to undergo a lot of dynamic

stretching and you know expansion that

are key to their function come down in

this section here this is from loose

connective tissue you can see this

thready like structure here this is an

actual elastic fiber where the arrow is

pointing come over to this section here

this is an elastic artery and then if

you look in this section here this is

the muscular layer of the artery so if

we draw a cross section here of the

artery

you have the endothelial layer which

faces the lumen then you have the

muscular layer like this and then you

have the adventitia layer and we'll go

over in more detail in this in the

cardiovascular lectures but this

muscular layer here

is what contains the elastic tissue and

you can actually stain for elastin using

an elastin stain it's just in the name

and you can see these long dark fibers

trying to underline them here so you can

see them they're very numerous as you

can see throughout this muscular layer

and again that contributes to its

ability to expand and then resume its

native shape synthesis of elastin like

collagen is synthesized by fibroblasts

and so it's the synthesis is very

similar to collagen and a lot of the

terms are very similar so you have

within the cell here and then you have

outside the cell here

and tropoelasin

is synthesized within the cell and then

it undergoes exocytosis

to go outside the cell

and then outside the cell you have lysal

oxidase again which catalyzes

oxidation reaction of lysine residues to

generate these reactive aldehydes in the

alasine which enable tropo elastin

proteins to cross-link and form elastin

and so if you have a couple different

tropo elastin molecules like this

lysol oxidase allows them to cross-link

like that

and that's what forms elastin

so you have tropoelastones which then

cross-linked to form elastin similar to

tropo collagen fibers which cross-linked

to form collagen fibers elastin is

broken down by elastase so this is

broken down by

the enzyme known as elastase and then

alpha-1 antitrypsin

inhibits and this can be important in

the in the disease we'll talk about in

the clinical pearls section

elastin contains a high amount of

non-hydroxylated

proline glycine and lysine residues so

the elastic fiber so once you have

elastin then you need to create the

elastic fiber so these are produced by

fibroblasts and arterial smooth muscle

cells so to help contribute to that

flexibility of larger arteries so you

have fibrillin which is a glycoprotein

that's synthesized and secreted by

fibroblasts in the extracellular matrix

and so we'll draw just kind of a cartoon

here so this will be your

fibrillin here

so this will be a glycoprotein

that was secreted by the fibroblast

and then the fiberglass would have also

secreted the elastin

which then is

cross-linked like this

and so

fibrillin serves as a major component of

the microfiber scaffold for deposition

of elastin so you have the fibrillin

molecule here and then

these cross-linked elastins come down

and they deposit onto

onto the

fiberline like this and then they can

come on this side too

and so these neighboring elastic

molecules they aggregate on here onto

the microfiber scaffold and then they

further cross link with each other like

this

and what happens is this completes the

composition of the elastic fiber so the

elastic fiber

is both the elastin

and the microfiber scalp fold which is

the main component of that is this

fibrillin here so all of this

is elastic fiber

so elastin has a further component to it

so you have you create the elastin

which is these cross-linked tropo

elastins here then they aggregate on

fibulin and then further cross-link and

aggregate together and that's what forms

your elastic fiber

thank you for watching this video from

the davinci academy histology video

course

which is completely available on youtube

to access the corresponding practice

questions and histology lab videos go to

our website using the link in the

description below

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