CHAPTER 4
Connective Tissue
65
Figure 4-7.
Collagen f brils
and
f broblasts.
EM,
3
14,000
Sometimes, the term
f brocyte
is used
to designate an
inactive f broblast
such as the cell seen in this electron
micrograph. The quiescent state of
the cell can be inferred from the scant
cytoplasm and small nucleus in which
heterochromatin
is the predominant
form of
chromatin
. The small circles
that F
ll the extracellular space are
type
I collagen f
brils
, which are uniformly
cut in cross section in this specimen of
dura mater, the tough outer layer of
the meninges.
There are many types of collagen
F bers in humans; types I, II, III, IV, V,
and VII are some of the most common
types. Collagen F
bers are the princi-
pal F
bers and are most abundant in
the connective tissue. Collagen F
bers
are fl
exible and have a high tensile
strength.
Fibroblast
Fibroblast
Type I
Type I
collagen fibrils
collagen fibrils
Heterochromatin
Heterochromatin
Cytoplasmic
Cytoplasmic
process
process
Cytoplasmic
process
Heterochromatin
Fibroblast
Type I
collagen fibrils
Type of
Collagen Fibers
Synthesizing Cells
Main Location
Main Function
Example of Collagen
Disorders
I
±ibroblasts, osteoblasts,
odontoblasts
Skin, ligaments, tendon,
bones, dentin
Resists force and
tension
Osteopsathyrosis
(fragilitas ossium or
osteogenesis imperfecta);
Ehlers-Danlos syndrome
II
Chondroblasts,
chondrocytes
Hyaline and elastic
cartilages
Resists pressure
Kniest dysplasia;
collagenopathy, type II
III
±ibroblasts, reticular
cells, hepatocytes, smooth
muscle cells
Reticular F bers in organs
(e.g., spleen, lymph node,
liver), blood vessels, skin
±orms structural
framework in
expansible organs
Ehlers-Danlos syndrome
IV
Endothelial cells,
epithelial
cells, lens epithelial cells
Basement membrane
(epithelium), lens capsule
(eye), glomerulus (kidney)
Provides support and
F ltration
Alport syndrome
V
Mesenchymal cells,
F broblasts, osteoblasts,
cementoblasts
Placenta, dermis, most
interstitial tissues, bones,
and cementum
Controls the
initiation
of collagen F bril
assembly; associated
with type I collagen
Classical Ehlers-Danlos
syndrome
VII
Keratinocytes
Basement membrane
Anchors
epidermal
basal lamina
to underlying
connective tissue
Epidermolysis bullosa
TABLE 4-1
Major Collagen Fibers
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