Transcript Connective Tissues Fibers and Ground Substance

Connective Tissues
Fibers and Ground
Substance
By
Dr. Muhammad Rafique
Assistant Professor
Anatomy Department
4-02-2008
Objectives
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Enumerate the different type of C. T. cells
Enumerate the different type of C. T. Fibers
Discuss the Collagen fibers
Describe the Reticular fibers
Describe the Elastic Fibers
Discuss the Ground Substance
Describe the different Component of Basement membrane
Discuss the Basement Membrane
Describe the different parts of Basement membrane
Connective Tissues
The connective tissues are the
gluing material that bound
the different Structures
together. A connective
tissue consists of the
different types of cells,
fibers and ground
substance. The fibers are
embedded in the ground
substance, now ground
substance along fibers is
called as Matrix
Connective Cells
I – Fixed Connective tissues
Cells
Fibrocytes (or fibroblasts)
Fat cells (Adipocytes)
II - wandering cells.
Histocytes (Macrophages)
Monocytes
Lymphocytes
Plasma cells
Eosinophils
Mast cells
Types of Connective Tissue Fibers
• Collagen Fibers: most
widely distributed in the
body formed by the
Fibroblasts
• Reticular Fibers mostly
present in Basement
membrane and capsules of
different organs
• Elastic Fibers are mainly
found where the Elasticity
is required
Collagen Fibers
• Collagen fibers are also
called as white fibers. They
are arranged in the bundles
with average length of 10 to
100 mm, the individual fiber
has average diameter of 1 to
2 mm. when each collagen
fiber examine under high
magnification, it consists of
thin collagen fibrils with of
diameter 0.2 to 0.5 mm. The
collagenous fibrils are
arranged parallel, giving
appearance of striation.
Structure of Collagen Fibers
On Electron Microscopic
examination revealed that each
collagenous fibril consists still
thinner microfilament with
average length on 300 nm and
diameter of 3 to 15 nm. Each
microfilament is formed the
macromolecule which is called
as the Tropocollagen. Each
tropocollagen consists of three
polypeptide chains interwined
together in form of a triple
helix. The polypeptide chain is
called is called an alpha chain.
Striations
• The microfilaments arranged
together to form collagenous
fibrils. The tropocollagen
arranged in such way that
they are parallel to each
other and they lying side by
side, they are arranged in
staggered fashion. One
molecule is overlapped by
the molecule by its one
quarter length. The space
between two adjacent is 40
nm
64 nm Banding
This arrangement gives a
typical appearance that
after each 64 nm, there is
light band, followed by
dark band. This will give
typical cross striations in
some of collagen fibers.
This is called as 64 nm
periodicity or 64 nm
banding under EM
Microscope.
Types of Collagen Fibers
There are many different
tropocollagen types around
(currently named type I to
XXI). These types differ in their
content of the amino acids
hydroxyproline and
hydroxylysine. They also differ
in the amount of carbohydrates
attached to the collagen
molecules. The different types
of tropocollagen give the fibers
the structural and functional
features which are appropriate
for the organ in which the fibers
are found.
Types of collagen
• Collagen occurs in many places throughout the body. There
are 28 types of collagen described in literature. Over 90% of
the collagen in the body, however, are Collagens I, II, III,
and IV. A simple way to remember their general functions
is:
• Collagen One - Bones (main component of bone)
• Collagen Two - Cartilages (main component of cartilage)
• Collagen Three - Reticular (main component of reticular
fibers)
• Collagen Four - forms the basement membrane
Types of collagen Fibers and Distribution
Type
Structural Details
Localization
300 nm, 67nm banded fibrils
skin, tendon, bone, etc.
II
300 nm, small 67nm fibrils
no band
cartilage, vitreous humor
III
300 nm, small 67nm fibrils
banded
skin, muscle, frequently with
type I
IV
390 nm no band
all basal lamina
I
Types of collagen Fibers and Distribution
V
390 nm no band
most interstitial tissue,
assoc. with type I
VI
150 nm,
most interstitial tissue,
assoc. with type I
VII
450 nm
epithelia
VIII
?, ?
some endothelial cells
Types of collagen Fibers and Distribution
IX
200nm
cartilage, assoc. with type
II
X
150nm
hypertrophic and
mineralizing cartilage
XI
300nm, small
fibers
cartilage
XII
?, ?
interacts with types I and
III
Reticular fibers or reticulin
Reticular fibers or reticulin is
a histological term used to
describe a type of structural
fiber composed of type III
collagen. Reticular fibers
crosslink to form a fine
meshwork (reticulum).
This network acts as a
supporting mesh in soft
tissues such as liver, bone
marrow, and the tissues and
organs of the lymphatic
system
Structure
Reticular fiber one or more types
of very thin and delicately
woven strands of type III
collagen, these strands build a
highly ordered cellular network
and provide a supporting
network. Many of these types of
collagen have been combined
with carbohydrate. Thus, they
react with silver stains and with
periodic acid-Schiff reagent but
are not demonstrated with
ordinary histological stains such
as those using hematoxylin.
Formation & Distributions
• Secreted by the fibroblast
and Reticular Cells
• Dermis of Skin, connective
sheath surrounding the
muscle, blood vessels,
intestine, uterus, urinary
bladder The reticular fibers
are also found spleen,
thymus, lymph node and
Tonsils
Elastic fibers (or yellow fibers)
are bundles of proteins
(elastin) found in
connective tissue and
produced by fibroblasts
and smooth muscle
cells in arteries. These
fibers can stretch up to
1.5 times their length
Formation of Elastic Fibers
Elastic fibers, as the name
suggests, are highly elastic
and stretch in response to
tension. In particular they
are formed from the protein
elastin. The amino acid
composition of elastin,
similar to collagen, is rich in
glycine and proline, but in
addition has two unusual
amino acids, desmosine and
isodesmosine. Elastic fibers
also have a high content of
valine.
Elastic Fibers
• Elastic fibers, as the name
suggests, are highly elastic
and stretch in response to
tension. In particular they
are formed from the protein
elastin. The amino acid
composition of elastin,
similar to collagen, is rich
in glycine and proline, but
in addition has two unusual
amino acids, desmosine
and isodesmosine. Elastic
fibers also have a high
content of valine.
Structure of Elastic Fibers
The Elastic fibers are highly
elastic and can easily be
stretched by weak traction
force and retrun to its original
length when these forces are
removed.
Elastic fibers are seen in
unstained preparation of loose
connective tissues as very thin
highly retractile strands with
0.2 to 1.0 mm, which branched
and rejoined to form a loose
network. In locations where
elastic fibers are abundant they
will produce yellow color to
tissues.
Staining Technique
In ordinary H & E stained
tissue section the elastic
fibers can not be
identified easily because
they are very faintly
eosinophilic. But they are
certain stain (for e.g.
Resorcin-fuchsin
technique for Elastic
Tissue) can demonstrate
the elastic fibers.
Development
Electron Microscopic studies
reveal that, during their
formation the elastic fibers pass
through three successive stages
which can be both in embryonic
and adult tissues. In initial stage
the fibers consists of thin
microfibrils, which are
composed of a glycoprotein
called fibrillin. In the next stage,
an amorphous substance of low
electron density appears in the
center of developing fibers. This
is called elastin. In the third
stage of elastic fibers
development, the amorphous
elastin component constitutes
more than 90% of fibers.
Distributions
The elastic fibers are
found in the ground
substance of
connective tissues
throughout the body.
For e.g. the lung,
large size arteries,
and certain ligaments
Ground substance
• Ground substance is a term for the non-collagenous
components of extracellular matrix. Cells are
surrounded by extracellular matrix in tissues, which acts
as a support for the cells. Ground substance
traditionally does not include collagen but does include
all the other proteinaceous components, including
proteoglycans, matrix proteins and, most prevalent,
water.
• Glycosaminoglycans
• sulfated variety includes chondroitin, dermatan, keratan, and
heparan
• non-sulfated
• hyaluronic acid
Proteoglycan
Molecules of these
sulfated
glycosaminoglycans
become covalently
attached as side chains to
an axial core protein.
The resulting structure,
termed a proteoglycan,
chondroitin-4-sulfate,
chondroitin-6-sulfate,
dermatan sulfate, heparan
sulfate, heparin
Adhesive glycoproteins
Help hold tissue structures together
much like mortar binds bricks.
One of these compounds,
fibronectin, links the
cytoskeleton of cells to collagen
fibers and other elements of the
extracellular matrix. Laminin
helps hold epithelial cells to the
basement membrane. Adhesive
glycoproteins contribute to the
ability of individual muscle
fibers to work as a unit by
holding them together when they
contract. Other members of the
adhesive glycoprotein family
play an important role in the
differentiation and growth of
cells, development of blood
vessels, and cell movement.
Basement membranes
Basement membrane is a
structure that supports an
overlying epithelium or
endothelium. Keratinocytes,
glandular cells, and endothelial
cells reside on basement
membranes. Basement
membrane consists of an
electron dense membrane
called basal lamina, about
300-700 angstrom in thickness,
and an underlying network of
reticular collagen fibrils which
average 300 angstrom in
diameter. This network is 0.1-2
micron in thickness.
The three parts of basement membranes
The lamina lucida
Above the lamina densa, next
to the cell membrane, is the
lamina lucida. This
electron-lucent layer is
traversed by delicate cords
that extend from the lamina
densa to the overlying cell
membrane. These cords are
thought to be composed, in
part, of the extracellular
portions of cell adhesion
molecules (integrins).
The lamina densa
• The lamina densa
• The middle part, called the
lamina densa, was
formerly called the basal
lamina. This layer
consists of laminin-5, type
IV collagen, which lacks
the axial periodicity seen
in other types of collagen,
and proteoglycans. The
lamina densa appears to be
a product of the cells to
which the basement
membrane is attached
(e.g., epithelial cells).
lamina fibroreticularis
Below the lamina densa,
next to the connective
tissue, is the lamina
fibroreticularis. This
electron-lucent layer
consists largely of
reticular fibers (type III
collagen) produced by
fibroblasts in the
underlying connective
tissue. There is also
some type VII collagen
here.
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