A BREIF STUDY OF CONNECTIVE TISSUE

1. Connective Tissue
DR Mubashar Iqbal

4. • Connective & supportive tissue connect other
tissues, provide a frame work, & support the
entire body by mean of cartilage & bones.
OR
• Connective tissue binds other tissues, vascular,
having abundant intercellular substance &
relatively few cells.
• Connective tissue develops from mesenchyme,
an embryonic type of tissue. Embryonic
connective tissue is present in the umbilical
cord and in the pulp of the developing teeth

5. • Connective tissue provide the mechanical
support, the connective tissue perform other
function as well.
• The ground substance part of the connective
tissue matrix serves as a medium through
which nutrients & waste products are
exchanges b/w the cells (epithelial &
muscular) & their blood supply.

6. • Connective tissue also plays important role ion
the defense of the body against injurious
agents; this is accomplished in the three ways .
1.The intercellular substances (matrix) of
connective tissue acts as a physical barrier to
those bacteria which manage to penetrate the
epithelial membranes.
2.Connective tissue cells (MAC) have ability to
engulf bacteria & other unwanted matter.
3.Some CN-tissue (plasma) produce antibodies
which react with & inactivate antigens.

7. Structure of the CN-tissue
• Connective tissue consists of cells &
intercellular substance or matrix. The matrix
is further composed of two components.
1.Amorphous ground substance
2. Thread-like formed elements called fibers.
• Different type of connective tissue differ from
each other in cell variety, chemical
composition of ground substance, & number &
kind of fibers.

8. • The connective tissue is classified as either
loose connective tissue or dense connective
tissue, depending on the amount, type,
arrangement, and abundance of cells, fibers,
and ground substance.
• Loose connective tissue. It is characterized
by a loose, irregular arrangement of connective
tissue fibers and abundant ground substance.
Numerous connective tissue cells and fibers
are found in the matrix. Collagen fibers,
fibroblasts, adipose cells, mast cells, and
macrophages predominate in loose connective
tissue, with fibroblasts being the most common
cell types.

9. • Dense connective tissue contains thicker and more
densely packed collagen fibers, with fewer cell
types and less ground substance. The collagen
fibers in dense irregular connective tissue exhibit a
random and irregular orientation. Dense connective
tissue is present in the dermis of skin, in capsules
of different organs, and in areas that need strong
support.
• In contrast, dense regular connective tissue
contains densely packed collagen fibers that exhibit
a regular and parallel arrangement. This type of
tissue is found in the tendons and ligaments. In
both connective tissue types, fibroblasts are the
most abundant cells, which are located between the
dense collagen bundles.

11. Cells of the Connective Tissue
• Many types of cells are found in different
varieties of connective tissue. Cell found in the
connective tissue proper will discussed here .
Fibroblasts & Fibrocytes:
Most common cell types in the connective
tissue. Fibrocytes are elongated & spindle-
shaped with processes that contact adjacent
cells & fibers .Nucleus is surrounded by scant
amount pale cytoplasm. at the TEM level, the
cytoplasm has sparse RER & a small golgi
complex.

12. • Free ribosomes,mitochondria, lysosomes &
vesicles are also presents.
• Actin filaments occur as bundles in the cell
processes.
• Fibrocytes maintain the CN-tissue matrix by
forming the fibers & constantly renewing the
ground substances.
Fibroblasts:
• These cells constitute the most abundant
variety of CN-tissue cells. the fibroblast appear
as large somewhat flattened, roughly ovoid
cells with branching processes.

13. • At the EM level, abundant rER & a prominent
Golgi complex are present in the cytoplasm.
There structural characteristics indicate more
active CN-tissue matrix production in
comparision to the fibrocyte. Fibroblast may
arise directly from undifferentiated
mesenchymal cells or are transformed from
fibrocytes under the influence of
microenviromentsal factors(cytokines).
• In certain situation fibroblast may differentiate
into adipose cells, chondroblasts, or
osteoblasts.

14.  Histocytes (Macrophages):
Are phagocytic cells and are most numerous in
loose connective tissue. They are difficult to
distinguish from fibroblasts, unless they are
performing phagocytic activity and contain
ingested material in their cytoplasm.
• They occur most frequently in the richly
vasularized areas of the body.
• Histocytes are imp agents of defence b/c of
their mobility & phagocytic properties, they
are able to act as scavenger cells. They engulf
dead cells extravasated blood cells, bacteria &
foreign bodies

15. Fibroblast
Fibrocytes
Adipose cell
Macrophages

17. Mast cells:
Mast cells, usually closely associated with
blood vessels, are widely distributed in the
connective tissue of the skin and in the
digestive and respiratory organs. Mast cells are
spherical cells filled with fine, regular dark-
staining and basophilic granules with centrally
placed pale-staining nucleus.
• Mast cells secrete heparin (a powerful
anticoagulant) & histamine ( a potent
vasodilator)

18. Plasma cells:
These cells are rare in CN-tissue but are numerous
in sites subject to the penetration of bacteria &
foreign proteins (e.g., the intestinal mucosa) & in
area where chronic inflammation is present.
• Plasma cells are large, ovoid cells, having a
basophilic cytoplasm. This basophilia is due to
abundance of RER. Nucleus of plasma cell is
spherical in shape & eccentric in position. With
the nucleus, chromatin occurs as course granules
arranged in a regular manner against the nuclear
membrane due to which the nucleus is said to
exhibit a cart-wheel appearance.

19. • Plasma cells are most numerous in lymphatic
tissue , especially in the center medullary cord
of lymph nodes. they are also particularly
abundant in bone marrow, the loose CN-tissue
underlying the epithelium of the G.I.T, the
respiratory system, & the female reproductive
system.
• Plasma cells do not originate in loose CN-
tissue but develop from B lymphocytes that
immigrate into CN-tissue from the blood; they
produce circulating or humoral antibodies

20.  Adipocytes:
Adipocytes are also referred to as adipose
cells. individual adipocytes or clusters
containing multiple cells are normal
components of loose CN-Tissue, but when the
far cells out number other cells types, the
tissue is called adipose tissue.
• The fat cells are large in size 50-150um in
diameter & have an ovoid or spherical shape.
• The cytoplasm is displaced to the peripheral
region of the cell by a single large fat droplet.
• Nucleus is flattened & found pressed against
the cell membrane

21.  Wandering cells:
These cells are not normally present in the
connective tissue but they are temporary
visitors from the blood & lymp stream.e.g
lymphocytes, eosinophils and neutrophils.

22. Fibers of the Connective Tissue
• Long slender protein polymers which are
found in differing productions in various types
of CN-tissue.
• Predominant fiber type is responsible
conferring specific properties to the tissue.
• CN-tissue fibers are of three major types
collage nous fibers, reticular fibers, and elastic
fibers, the ist two types (i.e, collagenous &
reticular) are composed of protein collagens,
while the elastic fibers are formed by the
protein elastin.

23. • Collagen Fibers
The collagenous fibers are the most commonly
occurring CN-tissue fibers. These are made up of
the protein collagens type 1 . Collagen fibers are
tough, thick, fibrous proteins that do not branch.
The collagenous fibers are flexible but
inelastic(i.e, non-extensible) and, thus they
provide a unique combination of flexibility &
strength to the structure in which they are present.
In H&E preparation examined under L/M,
collagen fibers stain acidophilic, taking a pink
colour with Eosin.

24. The most frequently recognized fibers in
histologic slides are the following:
1.Type I collagen fibers. (most abundant
occur)These are found in the dermis of skin,
tendons, ligaments, and bone & organ
capsules. They are very strong and offer great
resistance to tensil stresses.
2. Type II collagen fibers. These are present in
hyaline cartilage and elastic cartilage and in
vitreous body of the eye. The fibers provide
resistance to pressure.

25. 3. Type III collagen fibers. These are the thin,
branching reticular fibers that form the delicate
supporting meshwork in such organs as the
lymph nodes, spleen, and bone marrow.
4. Type IV collagen fibers. These are present in
the basal lamina of the basement membrane, to
which the basal regions of the cells attach.
5.Type V collagen fibers. It is mainly present in
fetal membrane and placenta.

26. • Reticular Fibers: (a very thin, branched
fibers, which form extensive network in
certain organs) .Reticular fibers, consist
mainly of type III collagen, are thin and form a
delicate net like framework in the liver, lymph
nodes, spleen, hemopoietic organs, and other
locations where blood and lymph are filtered.
Reticular fibers also support capillaries,
nerves, and muscle cells.

27. • Elastic Fibers
these fibers are highly elastic. They can be
stretched easily even by weak traction forces
but return to their original length when these
forces are removed.
Elastic fibers are found in abundance in the
lungs, bladder, skin,ligamenta flava,
ligamentum nuchae,pinna of ear, vocal cords,
epiglottis, musculars arteries.

30. Ground Substance of the
Connective Tissue
• Cell & fibers of the CN-tissue are embedded in
a highly hydrated gel which is called ground
substances. The water bound by ground
substance serves as the medium through which
all nutrients & waste products must pass in
transit between the blood and the parenchymal
cells of the organs.
• Ground Substance of the CN-tissue consist
mainly of proteoglycans.in addition it contain
adhesive glycoprotein, fibronectin & laminin.

31. • Several types of proteoglycans have been
isolated from the ground substance of the
connective tissue in different location with in
the body, these include hyaluronic acid,
chondroition sulfate, keratan sulfates 1 & 11,
heparan sulfate & dermatan sulfate .
• The adhesive glycoprotein fibronectin &
laminin play very important role in adhesion of
cells to the extracellular matrix.

32. BASEMENT MEMBRANE
• The extensive interface b/w CN-tissue &
various epithelia is characterized by the
presence of thin layers of extracellular material
which is called basement membrane(or basal
lamina).
• Composed of two layers
(1)Basal lamina-directly beneath the basal
plasmalemma of the epithelial cells.
(2) Reticular lamina—the thick layer, rich in
reticular fibers, merging into underlying CN-
tissue

33. • Under the EM basal lamina is seen to consist
of three layers or laminae, there is a central
electron-dense layer(called lamina densa)
having on either side an electron-lucent layers.
• There are two locations in the body where a
single basal lamina is found b/w two adjacent
epithelial layers
(1)Alveoli of the lung,
(2)Glomeruli of the kidney

34. Functions of the Basement Membrane
• bind the cells to the underlying or surrounding
CN-tissue
• Provide the epithelial cells a flexible support
capable of stretching & recoiling
• To serve as a molecular sieve or ultrafilter,
impeding the passage of macromolecules

35. Classification of CN-tissue
• Classification into various types depending on the
following four criteria.
(1)Relative proportion of the various fibers presents
(2) Compactness & arrangement of these fibers
(3)Nature of the matrix
(4)types of cells present
Above mention criteria CN-tissue are the following
two groups
(A)Embroyonal CN-tissue
(B)Adult CN-tissue

36. EMBROYONAL CN-TISSUE
• Developmentally, the CN-tissue are derived
from mesoderm which is one of the three
primary embryonic layers.
• The immature CN-tissue of the embryo
derived from the mesoderm is known as
mesenchyme. It is composed of roughly star-
shaped cells which lie in an abundant,
relatively homogenous intercellular substance.
• As the development proceeds, the
mesenchyme gradually assumes characteristics
of Adult CN-tiisue.

37. • The first changes appears of fibers in the
intercellular substance which thus becomes
more viscous .
• The embryonic CN-tissue of this stages is
known as mucous tissue. Widely distributed in
the body of fetus. The umbilical cord also
contain a considerable amount of mucous
tissue .

38. ADULT CN-TISSUE
• Divide into mail three varities
1. CN-tisue proper
2. Cartilage
3. Bone
1. CN-tissue proper discuss earlier as loose &
dense CN-tisse

39. CARTILAGE
• Cartilage is a special form of connective tissue
that also develops from the mesenchyme.
Similar to the connective tissue, cartilage
consists of cells and extracellular matrix
composed of connective tissue fibers and
ground substance. In contrast to connective
tissue, cartilage is nonvascular(avascular) and
receives its nutrition via diffusion through the
extracellular matrix(cappilaries located in
adjacent CN-tissue) or synovial fluid present in
joint cavities. there is no lymphatic vessels or
nerves in the cartilage.

40. Perichondrium
• It is a special capsule like structure , composed
of dense irregular connective tissue that
surrounds cartilages in most places. the
perichondrium contain blood vessels which is
responsible for the supply of nutrients &
oxygen to the perichondrium is seen to be
composed of two layers.
1.Outer fibrous layer which contains
collagenous & elastic fibers, fibroblast & large
blood vessels.

41. 2. Inner cellular layers which lodges cartilages
forming cells known as chondroblasts. In
addition, this layer contains fine blood vessels
and a few collagenous fibers.

42. Cartilage Types
• Hyaline Cartilage (glass like):
its intercellular substance appears clear &
uniform & the fibers, although present, are not
visible under the LM stained sections.
this cartilage is mostly widely distributed
cartilage in the body. it is very flexible & some
what elastic and is covered by perichondrium
except for articular cartilages of the synovial;
joints, which obtain their nutrients & oxygen, by
diffusion from the synovial fluid.

43. Cells Of Hyaline Cartilage
• Cells are chondrocytes. These are large
roughly spherical cells, each containing a bid
centrally- placed nucleus one are more nuclei.
• The cytoplasm is finely granular & moderatly
basophilic.
• The chondrocytes lie with in small cavities in
the matrix. These cavities are called lacunae.
• In the lacunae are mature cartilage cells called
chondrocytes. The main function of
chondrocytes is to maintain the cartilage
matrix.

44. Arrangement of chondrocytes
• In the central region of the hyaline cartilage,
the cells are generally arranged in groups
known as isogenous groups.the cells of a group
are spherical or ovoid in shape and are
flattened on adjacent sides. All the members of
an isogenous groups occupy a single lacuna

45. Hyaline Cartilage Matrix
• It is imp to know that the apparently homogenous
matrix of hyaline cartilage contains numerous
fibrils composed of collagen types 11.these fibrils
are masked by ground substances because of the
following two reasons.
1.The fibrils are very fine being 10-25nm in
diameter .hence they are beyond the resolving
power of the LM
2.The fibrils & ground substance have nearly the
same refractive index. resulting in a lack of
contrast between these two components.

46. • The type 11collagen fibrils can easily be seen
E/M. they are not arranged into bundles but
form a fine network.
• Due to the abundance of chondroitin sulfate.
The hyaline cartilage matrix appears
basophilic in routine H&E preparation.
• The region immediately around an isogenous
cell group stain intensely basophilic b/c it
contain large amounts of chondroitin sulfate
but relatively small numbers of collagenous
fibrils .such regions are known as territorial
matrix or capsule (of the lacunae)

47. • That matrix which lies b/w the cells groups
contains relatively smaller amount of
chondroitin sulfate & thus stain lightly
basophilic .thus matrix is known as
interterrittorial matrix.
Distribution of hyaline cartilage :
• ribs (costal cartilage), nose, larynx, trachea,
and in bronchi. Here, the hyaline cartilage
persists through out life and does not calcify.

48. hyaline cartilage

52. Fibrocartilage
• Fibrocartilage is characterized by large
amounts of irregular and dense bundles of
coarse collagen fibers in its matrix. In contrast
to hyaline and elastic cartilage, fibrocartilage
consists of alternating layers of cartilage
matrix and thick dense layers of type I
collagen fibers.
• In fibrocartilage the cells are not arranged as
groups but instead they form shorts rows.
abundance of collagens fibers gives a general
acidophilic reaction to the matrix .

54. • This type of cartilage is not covered by a
perichondrium.
• The collagen fibers normally orient themselves
into the direction of functional stress.
Fibrocartilage has a limited distribution in the
body and is found in the intervertebral discs,
discs of symphysis pubis, and certain joints.

55. Elastic Cartilage
• Elastic cartilage is similar in appearance to
hyaline cartilage, except for the presence of
numerous branching elastic fibers within its
matrix which branched and interlace with each
other to form a closely woven network.
• The elastic fibers, the matrix also contains
fibrils composed of collagens type 11.
• The elastic fiber covered by perichondrium.
• Elastic cartilage is highly flexible and occurs
in the external ear, walls of the auditory tube,
epiglottis, and larynx.

56. Elastic cartilage

58. BONE
• Bone special form of connective tissue and
consists of cells, fibers, and extracellular
matrix. Because of mineral deposition in the
matrix, bones become calcified .
• As a result, bones become hard and can bear
more weight than cartilage, serve as a rigid
skeleton for the body, and provide attachment
sites for muscles and organs.

59. • Bone also protects the brain in the skull, heart
and lungs in the thorax, and urinary and
reproductive organs between the pelvic bones.
In addition, bones function in hemopoiesis
(blood cell formation), and serve as crucial
reservoirs for calcium, phosphate, and other
minerals.
• Bone function metabolically providing a
source of calcium to maintain proper calcium
levels and various growth factors.

60. Bone Cells
• Osteoblasts:
Bone forming cells which synthesize & secrete
unmineralized bone matrix, the osteoid.
They also secrete the enzyme alkaline
phosphatase which brings about mineralization
of the which brings about mineralization of the
osteoid.
The active osteoblast (e.g., in a developing
bone) are roughly cuboidal in shape each
having a large spherical nucleus, which is
usually eccentric in position.

61. • The cytoplasm appears markedly basophilic in
the routine H&E stained sections. E/M reveals
but the basophilia is due the presence of a
large quantity of rough endoplasmic reticulm.
• The inactive or resting osteoblast (also called
bone linning cells) appear as fusiform (spindle-
shaped) cells having very slightly basophilic
cytoplasm and a small darkly staining nucleus.

62. • Osteocytes:
The osteocytes are mature bone cells, derived
from osteoblasts, which have secrete bone
around them. They are flat almond shaped
cells possessing a faintly basophilic cytoplasm,
which contains a small amount of rough
endoplasmic reticulum and a small Golgi
apparatus.
The osteocytes lie with in small
cavities(lacunae) in the bone matrix. lacunae
communicate with each other by narrow
tubular channels called canaliculi.
.

63. • fine cytoplasmic processes from each oosteocyte
extend for some distance into the canalculi & make
contac with similar processes from neighbouring
cells.
• Gap junction are present where the cytoplasmic
processess contac each other .these junctions
provide for intercelluar flow of ions & small
molecules .
• The intercellular flow provides a mechanism by
which nutrients & metabolites can be exchanged
b/w the blood vessels(present in the periosteum or
haversion canals) & distant osteocytes which lie
imprisoned with in the impermeable bone matrix

64. • Osteoclasts:
large multinucleated cells found along bone
surfaces where resorption(removal of bone),
remodeling, and repair of bone take place.
The main function of osteoclasts is bone
resorption during remodeling (renewal or
restructuring) and calcium haemostasis.
Osteoclasts are often located on the resorbed
surfaces or in shallow depressions in the bone
matrix called Howship’s lacunae. Lysosomal
enzymes released by osteoclasts erode these
depressions.

65. Bone Matrix
• The bone matrix consists of living cells and
extracellular material. Because the bone matrix
is calcified or mineralized, it is harder than
cartilage.
• Bone matrix contains both organic and
inorganic components. The organic
components enable bones to resist tension,
while the mineral components resist
compression.

66. • The major organic components (35% of the
dry weight of the bone) of bone matrix are the
coarse type I collagen fibers, which are the
predominant proteins & amorphous ground
substance(proteoglycan of bone is chondroitin
sulphate ).
• The inorganic component (65% of the dry
weight of bone) of bone matrix consists of the
minerals calcium and phosphate in the form of
hydroxyapatite crystals. The association of
coarse collagen fibers with hydroxyapatite
crystals provides the bone with its hardness,
durability, and strength.

67. Bone Formation (Ossification)
• Bone formation process starts in the early
intrauterine life & continuous into adult hood
of the person. the bony tissue ,like all other
types of CN-tissue, is derived from
mesenchyme .
• Bone developed from mesenchyme by two
method.
1.Intra membranous ossification
2.Endochondral ossification

68. Intramembranous Ossification
• The process of intramembranous ossification
begins in the second month of intrauterine life.
• In this type of ossification mesenchyme is
directly converted into bone with out
intervening stage of cartilage formation.
• Some mesenchyme cells differentiate directly
into osteoblasts that produce the surrounding
osteoid matrix, which quickly calcifies.
Numerous ossification centers are formed,
anastomose, and produce a network of spongy
bone that consists of thin rods, plates, and
spines called trabeculae.

69. • The osteoblasts then become surrounded by
bone in the cavelike lacunae and become
osteocytes. As in endochondral ossification,
once osteocytes are in the lacunae, they
establish a complex cell-to-cell connection
through the canaliculi. The mandible, maxilla,
clavicles, and most of the flat bones of the
skull are formed by the intramembranous
method.

70. Endochondral Ossification
• In this type of bone formation, the
mesenchyme is the first converted into
cartilage which serves as temporary supportive
framework. this cartilage is then replace by
bone. this processes may be called indirect
method of bone formation
• Most bones in the body develop by the process
of endochondral ossification, in which a
temporary hyaline cartilage model precedes
bone formation.

71. • The chondrocytes divide, hypertrophy
(enlarge), and mature, and the hyaline cartilage
model begins to calcify.
• Calcification of the cartilage model continues,
diffusion of nutrients and gases through the
calcified matrix decreases
• Chondrocytes die and the fragmented calcified
matrix serves as structural framework for the
deposition of bony material
• layer of bony material is deposited around the
calcifying cartilage, the inner perichondrial
cells exhibit their osteogenic potential

72. • Thin periosteal collar of bone forms around the
midpoint of the shaft of the bone.
• This external surrounding connective tissue is
now called the periosteum. Mesenchyme cells
differentiate into osteoprogenitor cells from the
inner layer of periosteum, and blood vessels
from the periosteum invade the calcified and
degenerating cartilage model.
• Osteoprogenitor cells proliferate and
differentiate into osteoblasts that secrete the
osteoid matrix, a soft initially collagenous
tissue that lacks minerals but is quickly
mineralized into the bone.

73. • The osteoblasts are then surrounded by bone in
the cavelike lacunae and are now called
osteocytes;there is one osteocyte per lacuna.
Osteocytes establish a complex cell-to-cell
connection through tiny canals in the bone
called canaliculi; these eventually open into
channels that house the blood vessels.
Osteoprogenitor cells also arise from the inner
surface of bone called endosteum.
• Endosteum lines all internal cavities in the
bone and consists of a single layer of
osteoprogenitor cells.

74. • Primary ossification center forms in diaphysis
and secondary center of ossification in
epiphysis
• Epiphyseal plate between diaphysis and
epiphysis allows for growth in bone length
• All cartilage is replaced except the articular
cartilage

75. Endochondral Ossification:
Development of a Long Bone
• The plate of cartilage intervening b/w the
diaphysis & epiphysis is known as epiphyseal
cartilage or growth plate . this plate is
responsible for the longitudinal growth of the
bone during childhood & early adult age.
Starting from epiphyseal side following
successive zones can be recognized in the
epiphyseal cartilage.

76. 1. Zone of reserve cartilage:
2. Zone of proliferating chondrocytes:
3. Zone of lacunar Enlargement & cellular
Hypertrophy:
4. Zone of Cartilage Calcification:
5. Zone of Cartilage removal & bone deposition:

78. Microscopic Structure of the Bone
Tissue Osteon

80. Cancellous bone