CONNECTIVE TISSUE

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CONNECTIVE TISSUE

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Title: CONNECTIVE TISSUE

1
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.

2
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 blue- azure 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
5

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, light-staining collagen
fibers (arrows) are seen in this picture.

MC
6

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
7

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
8

This shows another plastic section of loose
connective tissue stained with methylene blue-
azure 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
9

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
10

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
14

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
15

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
21

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
22

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
23
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
25

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

27

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
29

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
31

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.

33
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
35

This shows a cross-section 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
36

This shows a higher magnification of the previous
slide illustrating developing bone.

Spongy Bone
Calcified Cartilage
37

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
38

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
39

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
40

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
42

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
43

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
44

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
45

This figure shows decalcified bone (B) and dense
connective tissue of an associated tendon (T)
attaching to the periosteum.

B
T
46

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
48

This illustrates bone marrow (BM) and the
osteoblasts (Ob) lining bone. The osteoblasts
extend into the beginning of a Volkmanns Canal
(VC), which carries blood vessels into the
Haversian system.

BM
Ob
VC
49

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
50

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
51

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
52

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
53