CONNECTIVE TISSUE
“Tug of War” (Detail)
Frederick Morgan
CONNECTIVE TISSUES
Collagenous Connective Tissue
• Basic stained with Masson’s method
Tissues with
supportive
functions:
– Structural
– Nutritive
• Major
subdivisions:
– CT Proper ( =
Fibrous CT)
– Special CT
– Cartilage and
Bone
– Blood
COMPONENTS OF CT
• All CT’s have three components:
– Extracellular Matrix
– Extracellular Fibers
– Characteristic cell types
• Proportions vary widely
– Ratio determines properties
• All CT’s have similar components
and share cell types
THE MATRIX
• Fibrillar components and cells reside in
an amorphous matrix
– Produced by CT cells
– Usually a viscous liquid or gel
– Invariably contains glycoproteins and/or
proteoglycans
• Strongly PAS+
• Most important component is hyaluronic acid
– Fills interstices of the tissue
– Barrier to bacteria
– Shock absorber
FIBERS OF CT’S
• COLLAGEN
– “Reticular fibers”
• ELASTIC FIBERS
COLLAGEN
• Most common protein
in animals
• Present in all CT’s to
some extent
• Many different types
known
• Confers strength and
tearing resistance to
CT’s
• Most types have a
typical appearance in
EM as “banded” fibrils
COLLAGEN TYPES
Clockwise from upper left,
Type I, Type III, Type IV
• Type I: most abundant; skin, bone, tendon, Type II: unbanded; found
in cartilage
• Type III: “Reticular fibers”
• Type IV: unbanded; major component of basement membranes
A BIOLOGICAL “ROPE”
• Multi-strand
construction
with
overlapping
monomers of
tropocollagen
• Confers
conspicuous
banding
pattern in TEM
ORIGIN OF THE BANDING PATTERN
Staggering of overlap
creates pattern of light &
dark bands at 640Å
intervals
NOT ALL COLLAGEN IS
BANDED!
CHEMISTRY OF COLLAGEN
• Three different strand types
– Monomers synthesized intracellularly; exported & “cured” in
glycocalyx
• Two unique amino acids
– Hydroxyproline
– Hydroxylysine
– Proportions vary: an assay for collagen content
COLLAGEN SYNTHESIS
Same pathway as
other protein
synthesis
Soluble precursor
(tropocollagen)
made
intracellularly
Tropocollagens
exported
Fibers assembled
& spun outside
cell!
“RETICULAR
FIBERS”
• Outmoded term still
used
• Chemically a form
of collagen, Type III
• Fibrils smaller than
most other collagen
Assembled as webs
and fine networks,
not bundles
“Reticular fibers” in a lymph node,
Wilder’s stain
“RETICULAR FIBERS”
• Associated
with blood
vessels and
lymphatics,
etc.
• Anchor
vessels &
nerve fibers
Always
associated
with other
collagen
types in vivo
• NOT COLLAGEN
– Chemically ELASTIC FIBERS
different
• Two
components:
fibrils &
amorphous
ground material,
elastin
• Confer
“springiness”
Much less
common than
collagen
• Always
associated with
collagen
• Form strands or
sheets
• Fibers contain
elastin
ELASTIC FIBERS IN SITU
Note size,
proximity to
collagen
fibers,
association
with
microfibrils
ELASTIC FIBERS IN CROSS SECTION
HISTOLOGY OF CT’S:
FIBROUS CT’s
• Also “CT Proper” in some references
• Fibers are principal elements
• Matrix moderate
• All cell types present
• Classified by density and
arrangements of fibers
– “Loose” Vs. “Dense”
– “Regular” Vs. “Irregular”
TYPES OF FIBROUS CT’S
• COLLAGENOUS
– Mainly collagenous fibers
• Elastic Fibers always present
– Most common type, many forms
– High tensile strength due to collagen
• ELASTIC
– Principally elastic fibers
• Collagen Fibers always present
– Form bands and sheets
– Provides for elasticity, resilience, shape
retention
CLASSIFYING FIBROUS CT’S
• FIBER
ORIENTATION
– Regular or
irregular
• FIBER PACKING
– Loose or dense
• FIBER TYPE
– COLLAGEN
– ELASTIC
“IRREGULAR”
Both “Dense” & “Loose” forms exist
“REGULAR”
Only the “dense” form exists!
REGULAR VERSUS IRREGULAR
TENDON: COLLAGENOUS DRCCT
NUCHAL LIGAMENT: DRECT
DENSE IRREGULAR CT
LOOSE IRREGULAR CT
• Usually very
cellular
• Cores of villi
• Internal
“scaffolding”
of some
organs
• Collagen,
elastic fibers
• Not easily
seen in LM
LOOSE IRREGULAR CT
CELLS OF CTs
• CT’s have MOST cell types in
common
– Most so-called “blood cells” are
really CT cells
• Cells make & maintain all
components of all CT
• Some cells function in CT only
• Most important &
abundant cell
FIBROBLAST
• Make fibers and
matrix
– Related by lineage
to cells with similar
capabilities
• Found among
fibers
• Long lived
• Proliferate and
become active if
needed
– “Mesenchymal”
cells a quiescent
reserve
ORIGINS
• Nearly all
CT cells
have
common
stem
• Some
variant of
the
fibroblast is
always
present
FIBROBLAST MAKING COLLAGEN
OUR FRIEND, THE MACROPHAGE
• Very common
in most CT’s
– Ubiquitous
phagocyte
• Shares lineage
with some
bone cells
– NOT from
fibroblast line
– May coalesce
to form
multinucleated TOP: Active
“giant” cells macrophage in
– Extremely situ; BOTTOM:
important in A giant cell
inflammatory
reaction
• Widely
distributed
MAST CELLS
• Functions not
completely
understood
– Allergic
reactions
– Granules contain
heparin and
histamine,
leukocyte
attractants
• May contain
serotonin
• Shared lineage
with basophil of
blood
MAST CELLS
LEFT: H&E RIGHT: Toluidine Blue
PLASMA CELLS
• An “activated” B
lymphocyte
– Site of production of
antibodies
• Very numerous under
epithelial sheets
• Accumulate in large
numbers when body’s
integrity is breached
• Characteristic
appearance
• Gradations exist
“SPECIAL CTs”
• Have “traditional” components but one
will predominate and confer overall
properties
• Types of “Special CT”:
– “Reticular”
– Adipose
– Mucous
“RETICULAR” CT
• Fibrous component
is “reticular fibers,”
i.e., Type III collagen
• Form 3-D webworks
• More cellular than
most CT’s
• Relatively little
matrix
• Found in:
– Stroma of lymphatic
organs
– Anchoring BV’s
– Hemopoietic areas
MUCOUS
CT
• Not normally found in
adult mammals in any
significant amount
• Matrix material
predominant element
• Gooey and wet
• Fibers very scanty; cells
scattered
“Wharton’s Jelly” of umbilical cord >
ADIPOSE CT
• Adipose cells are scattered in other CT’s
– Singly or in clumps in any loose CT and some
dense ones
– Functions of adipose tissue are broadly protective
and supportive
• Two forms: “White” and “Brown”
• Cells occur
singly or in
WHITE ADIPOSE CT
depots in
fibrous CT
• “Chicken
wire”
appearance
• Single
droplet of
lipid
• Energy
storage and
shock
protection
functions
WHITE
FAT CELLS
• Single large fat droplet
– Not membrane-bound
• Normal organelles are
present
– Nucleus displaced
• Wide distribution
• Long lived and non-
dividing
• Principal functions as
energy reserve and
cushioning
BROWN FAT
• Despite “glandular”
appearance, NOT
secretory!
• Limited distribution
– Of most importance in
younger mammals
• Mitochondria content
high
• Uncouples
dephosphorylation of
ATP>ADP
• Only function is heat
generation
BROWN • Lipid bodies are multiple
• Mitochondria & BV’s give it
FAT “brown” color in gross
specimens
“HE WAS
THE
NOBLEST
RODENT OF
THEM ALL”
--William
Shakespeare
