Connective Tissue Fibers Histology [Connective Tissue Histology Part 1 of 3]
Summary
TLDRThis 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
- đ The Da Vinci Academy's histology video course is available on YouTube, covering fundamental principles of histology and relevant cell biology.
- đ The course includes a histology playlist and additional resources such as practice questions and lab videos accessible through their website.
- đ Connective tissue is one of the four main tissue types and includes various tissues like cartilage, bone, adipose tissue, and specialized connective tissues.
- 𧏠Connective tissue is characterized by a higher proportion of extracellular matrix compared to cells, with supportive fibers like collagen and elastin being predominant.
- đ 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.
- đ” Connective tissue elements mostly originate from mesenchyme, the embryonic connective tissue, and the mesoderm germ layer.
- đ Extracellular matrix is composed of extracellular fibers, ground substance, and fluids, including collagen, reticular fibers, elastic fibers, glycoproteins, proteoglycans, and glycosaminoglycans.
- đ Fibroblasts are the primary cells found in connective tissue proper, with other cells like adipocytes, white blood cells, and mast cells also present.
- đȘ 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.
- đ 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.
- đ 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
đ 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.
đ© 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.
𧏠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.
đ 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.
đ 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.
Mindmap
Keywords
đĄConnective Tissue
đĄExtracellular Matrix
đĄFibers
đĄCollagen
đĄElastin
đĄEpithelial Tissue
đĄMesenchyme
đĄGerm Layers
đĄFibroblasts
đĄWound Repair
đĄLoose Connective Tissue
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
foreign
foreign
[Music]
so
[Music]
you
Voir Plus de Vidéos Connexes
5.0 / 5 (0 votes)