CONNECTIVE TISSUE
Connective tissue is composed of cells
surrounded by an extensive extracellular
matrix. There are a number of different
types of connective tissues that are
classified by the organization and
composition of the cellular components
and the extracellular matrix. The following
slides demonstrate and describe these
connective tissues and their components.
Basic Connective Tissue Types
• The basic connective tissue types include
loose connective tissue, dense irregular
connective tissue and dense regular
connective tissue. These are classified
based on the relative density and
organization of the extracellular matrix
components. There are a number of cell
types that are resident to connective
tissue. These are described in
subsequent slides.
• This shows a thin,
plastic section of loose
connective tissue from
the oviduct stained
with methylene blueazure II. This type of
connective tissue is
very cellular and has
few collagen fibers.
The large elongated
cell (arrow) is a
fibroblast with an oval
nucleus and much
euchromatin.
• This shows loose
connective tissue from
the mammary gland
stained with hematoxylin
and eosin. The loosely
arranged collagen fibers
(arrows) are acidophilic
and lightly stained in this
picture. A mast cell with a
round nucleus is seen
(MC) with a considerable
amount of
heterochromatin.
Eosinophilic secretory
granules fill the cytoplasm
of this cell.
MC
• This shows loose
fibrous connective
tissue similar to that
seen in the previous
slide. Another mast
cell (MC) is located
near the center of the
field. Thin, lightstaining collagen
fibers (arrows) are
seen in this picture.
MC
• This shows a spread (not a
tissue section) of a thin piece
of mesentery illustrating a
different view of loose
connective tissue. The large,
dark-staining cells are mast
cells (MC) whose granules
obscure the nuclei. The
largest oval nuclei belong to
mesothelial cells (Me), that
form an epithelium on either
side of the connective tissue.
The smaller, oval nuclei
belong to macrophages
(Ma). These cells tend to
have associated granular
material in their cytoplasm.
Other oval-shaped nuclei
seen here are those of
fibroblasts.
Ma
Me
MC
• This shows a
transmission electron
micrograph of a mast
cell illustrating
numerous dense
secretory granules in
the cytoplasm. Note
also the elongated
nucleus (Nu) with
abundant
heterochromatin.
Nu
• This shows another
plastic section of loose
connective tissue stained
with methylene blueazure II. A number of
fibroblasts are seen (Fi)
with oval euchromatic
nuclei. A monocyte (Mo)
is also seen with a darker,
indented nucleus. A
binucleate neutrophil (N)
and a macrophage (Ma)
with a small, light-staining
nucleus are also seen.
Mo
N
Fi
• This shows two plasma
cells (PC) located in the
loose connective tissue of
the mammary gland.
These cells have round,
eccentric nuclei with
slightly basophilic
cytoplasm (indicating the
presence of RNP). The
large, pale nucleus is that
of a fibroblast while the
darker nuclei are those of
fibrocytes.
PC
• This shows adipose
tissue stained with
hematoxylin and eosin.
The lipid in these fat cells
is dissolved out during
the fixation and
embedding process.
Only a thin rim of
cytoplasm and the
flattened nuclei (arrows)
are seen.
• This shows a
developing adipose
cell (arrow) stained
with hematoxylin and
eosin. Note the ring
of cytoplasm and the
rounded nucleus
surrounding a lipid
droplet. Acidophilic
collagen fibers are
seen around the cell.
• This shows adipose
cells preserved so
that the lipid is
retained in the cell
and stained with
osmic acid, hence the
really dark
appearance of the
cells.
• This shows loose
connective tissue (CT)
within a mucosal fold in
the gall bladder.
Numerous collagen fibers
and abundant cells can
be seen in the connective
tissue. The cells cannot
be readily identified at
this magnification. (What
type of epithelium is seen
here?)
CT
• This shows a section of
the spermatic cord
illustrating dense irregular
connective tissue. In
dense connective tissues,
the abundant collagen
fibers form interwoven
bands of tissue. In
contrast to loose
connective tissue, there
are relatively few cells
(mainly fibrocytes). On
the edges of the tissue is
a simple squamous
epithelium (Ep).
Ep
• This shows dense
irregular connective
tissue at higher
magnification than in the
previous slide. The
bundles of brownish
collagen fibers can be
seen coursing in different
directions and different
planes. A few thinner,
darker staining elastic
fibers can be seen in this
section (arrows).
• This shows dense elastic
tissue of the aorta at low
magnification. The thin
elastic fibers (stained
black) in the wall of the
aorta (arrows) form layers
separated by spaces.
The collagen fibers are
stained brown in this
section.
• This shows another
example of dense
irregular connective
tissue from the urinary
bladder at low
magnification. This
particular section has
more cells than the
previous example, but still
fewer than the loose
connective tissue seen
earlier. Most of the nuclei
belong to fibrocytes.
• This shows another
picture of dense
irregular connective
tissue from the
urinary bladder. Note
that the collagen
bundles in the top of
the field are more
organized than those
at the bottom.
• This shows a section of
the penis illustrating
dense regular connective
tissue stained with
hematoxylin and eosin.
Most of the collagen
fibers (pink staining) are
oriented parallel to each
other. The nuclei of
fibrocytes are present.
• This shows dense regular
connective tissue (CT)
from a ganglion. On the
left side of the field are
elongated nuclei of
nervous tissue (NT). The
remainder of the field is
occupied by dense
collagenous fibers with
few, flattened nuclei of
fibrocytes.
NT
CT
• This shows a
transmission electron
micrograph of a
macrophage. The
nucleus (Nu) is
eccentrically located
and is relatively
heterochromatic.
Note the
lysosomes/residual
bodies (R) in the
cytoplasm as well as
mitochondria, rough
endoplasmic
reticulum. Also, note
the collagen fibrils
outside the cell (C).
Nu
R
C
• This shows a
transmission electron
micrograph of a
lymphocyte. Notice that
the nucleus (Nu)
occupies a large portion
of the cell, is indented
and has a fair amount of
heterochromatin. The
cytoplasm has only a few
organelles and the
plasma membrane tends
to be irregular due to
movement of the cell.
Nu
CARTILAGE
• Cartilage is a specialized form of
connective tissue composed of cells called
chondrocytes and their surrounding matrix.
There are three types of cartilage that are
distinguished based on their matrix
characteristics.
• This shows a light
micrograph of hyaline
cartilage located in the
trachea. The pieces of
cartilage (HC) are
bordered by dense
regular connective tissue
of the perichondrium (P).
The cartilage cells or
chondrocytes (arrows)
are located in lacunae
(these are difficult to
discern at this
magnification).
P
HC
• This shows a portion of
the previous picture at
higher magnification
illustrating the
chondrocytes in lacunae
(arrows). The matrix
surrounding the cells is
composed of collagen
fibers (too small too be
seen here) and other
components including
glycosaminoglycans such
as chondroitin sulfate.
• This shows hyaline
cartilage (HC) from the
nasal cavity illustrating
chondrocytes in their
lacunae and the “glassy”
appearance of the
surrounding matrix
(purple staining here).
Note the organization of
the dense regular
connective tissue of the
perichondrium (P) as
compared to the irregular
dense connective tissue
of the surrounding
connective tissue (*).
HC
P
*
• This shows a higher
magnification of
hyaline cartilage from
the trachea. The
chondrocytes on the
right side of the field
are not as mature and
fill their lacunae
(arrow) while those of
the left have more
space surrounding
the cell.
• This shows a section of
elastic cartilage stained
with a Verhoeff stain.
Identify the perichondrium
(P) surrounding the
cartilage. Note the
specifically stained elastic
fibers (arrows)
characteristic of this
cartilage type. Also
notice that the
chondrocytes and their
lacunae get larger as they
progress from the edge of
the cartilage towards its
center.
P
• This shows a higher
magnification view of
elastic cartilage. The
elastic fibers are more
clearly seen in this
picture as are the
chondrocytes and
their lacunae.
• This shows elastic
cartilage of the epiglottis
stained with a Trichrome
stain. Note that the
collagen of the
perichondrium (P) is
stained green; however,
the collagen type II within
the cartilage does not
stain. The elastic fibers
are stained purple
(arrows)
P
• This shows a light-stained
section of fibrocartilage.
The cartilage stains
acidophilic due to the
collagen fibers. Note that
the chondrocytes and
lacunae are small and
often have some regular
pattern to their
organization (in rows).
There is no
perichondrium associated
with this cartilage type.
• This shows a higher
magnification view of
fibrocartilage illustrating
the collagen fibers within
the matrix surrounding
the chondrocytes. This
type of cartilage is often
found between hyaline
cartilage and dense
connective tissue.
BONE
• Bone is a specialized connective tissue
with a mineralized extracellular matrix.
Bone generally consists of three cell types
including the osteoprogenitor cells,
osteoblasts (osteocytes when
differeniated) and osteoclasts. The
following slides illustrate some of the
features of bony tissue.
• This shows a low
magnification view of the
end of a long bone.
Above the epiphyseal
plate (EP) is spongy
bone. The outer portion
of the shaft is compact
bone (CB), which is laid
down by appositional
growth from the
periosteum. The
compact bone surrounds
the spongy bone and
bone marrow of the shaft.
EP
CB
• This shows a crosssection of developing
bone from a fetal finger.
The outermost layer is
the connective tissue of
the periosteum (P).
Small pieces of calcified
cartilage are seen (blue
staining) as are
hypertrophying cartilage
(arrows).
Tendon
P
Spongy Bone
Developing
Compact Bone
• This shows a higher
magnification of the
previous slide
illustrating developing
bone.
Spongy Bone
Calcified Cartilage
• This shows red blood
cells (RBC) in the
bone marrow
bordering pieces of
calcified cartilage
(arrows). The
calcified cartilage
(blue) is covered with
osseous tissue (deep
pink staining).
RBC
• This shows a
scanning electron
micrograph of bone
surface. Note the
Haversian Canals
(HC), the concentric
lamellae surrounding
these and the lacunae
of the osteocytes
(arrows).
HC
• This shows a section
of decalcified bone.
The structural
features are similar to
that in the previous
slide illustrating the
Haversian system.
Haversian Canal
Osteocytes
• This shows a
transmission electron
micrograph of an
osteocyte surrounded
by its lacuna. The
processes extending
from the cell body are
located in canaliculi
(arrows). The matrix
of the bone surrounds
the canaliculi.
• This shows a section of
decalcified bone and
associated skeletal
muscle (SM). The
skeletal muscle is
attached to the
connective tissue of the
periosteum (P). The
large space is due to
shrinkage of the
periosteum during
processing of the tissue.
Small Haversian Canals
can be seen within the
bone (arrows).
P
SM
• This shows a section of
decalcified bone
illustrating the connective
tissue of the perioosteum
(P). Osteoblasts are
located along the inner
edge of the periosteum
(arrow). These cells will
deposit and become
entrapped in bony matrix
(appositional growth).
P
Compact Bone
• This shows another
section of decalcified
bone and associated
skeletal muscle (SM).
Note that the osteogenic
layer of the periosteum is
quite cellular (arrows)
with basophilic
osteoblasts located at the
periphery of the bone.
SM
• This shows bony
tissue (upper right
corner) and the dense
irregular connective
tissue of the
periosteum (P). Note
that the indentation of
the periosteum into
the bone contains
looser connective
tissue. Lining the
periosteum are
basophilic-stained
osteoblasts (Ob)
Ob
P
• This figure shows
decalcified bone (B)
and dense
connective tissue of
an associated
tendon (T) attaching
to the periosteum.
B
T
• This shows
decalcified bone
illustrating a
resorption canal
surrounded by the
bony tissue.
Osteoclasts (arrows)
can be seen lying
next to the bony
tissue.
• This illustrates bone
marrow (BM) adjacent
to inner
circumferential
lamellae of bone.
The dark irregular
areas (arrows) are the
original calcified
cartilage indicating
that this was formed
by endochondral
ossification.
BM
• This illustrates bone
marrow (BM) and the
osteoblasts (Ob)
lining bone. The
Ob
osteoblasts extend
into the beginning of a
Volkmann’s Canal
(VC), which carries
blood vessels into the
Haversian system.
BM
VC
• This schematic
illustrates the process of
intramembranous
ossification.
Mesenchymal cells form
an elaborate network
(1). These cells then
enlarge and differentiate
into osteoblasts (2).
The cells lay down an
intercellular matrix an
form bony spicules (3)
covered by osteoblasts.
1
2
3
• This is a decalcified
section of the root of
a tooth and its
associated alveolar
bone (B). The root
of the tooth is
covered by
cementum (C) and
collagen fibers
which anchor the
tooth into the bony
tissue.
B
C
• This shows a high
voltage electron
micrograph of a
relatively thick plastic
section illustrating a
fibroblast (Fi) with
bundles of collagen
fibers attaching to the
cell surface (arrows).
Fi
• This shows another
high voltage electron
micrograph of
collagen fibrils
(arrows) attaching to
a myocyte (M). The
very thin filaments are
glycoproteins in the
extracellular matrix
while the dense
globular material is
proteoglycan (blue
arrows).
M
• This shows collagen
fibers attached to two
skeletal muscle cells
(SM) and a capillary
(C).
SM
SM
C
• This shows a
scanning electron
micrograph of a
fibroblast (Fi) within a
network of collagen
fibers.
Fi