- Connective tissue provides structure and support throughout the body by binding other tissues together. It is composed of cells and an extracellular matrix of fibers and ground substance. - The main cell types are fibroblasts, which produce the extracellular matrix, and also adipocytes, macrophages, mast cells, plasma cells, and leukocytes. - The extracellular matrix contains collagen fibers, elastic fibers, reticular fibers, and ground substance. Collagen provides strength, elastic fibers allow stretch, and reticular fibers form networks to support cells. - Connective tissue is found in every organ, where it provides structure in the stroma while other tissue types perform specialized functions in the parenchyma. It develops from mesenchyme and

1. Connective tissue
Asst Prof Ender Deniz Asmaz
Dept.of Histology&Embryology
Learning Objectives
• Classification of connective
tissue defines the composition
and organization of its cellular
and extracellular components and
basic features of tissue function.
• Tells the structure of embryonic
connective tissue.
• Classifies the main connective
tissue types and defines their
functional properties.
• Counts the connective tissue
threads, defines the molecular
and microscopic properties of the
threads.
• Counts the components of the
Extracellular Matrix and explains
its basic structure.
• Counts the connective tissue
cells, defines the microscopic and
functional properties of the cells.

2.  Connective tissue is one of the four tissues found
in the human body.
 Connective tissue provides a matrix that supports
and physically connects other tissues and cells
together to form the organs of the body.
 Connective tissue is found in between other
tissues everywhere in the body, including the
nervous system.
2

3. Organ Components:
3
 Most organs can be divided into:
The parenchyma, which is composed of the
cells responsible for the organ’s specialized
functions.
The stroma, the cells of which have a
supporting role in the organ. Except in the
brain and spinal cord, the stroma is always
connective tissue.

4. Most Organs Parenchyma Stroma
4

5. 5
 Connective tissue originates from the
mesenchyme.
 Atissue developing mainly from the middle layer of
the embryo, the mesoderm.
.
 Embryonic mesenchyme producing all types of connective
tissue proper and the specialized connective tissues bone and
cartilage, they also include stem cells for other tissues such as
blood, the vascular endothelium, and muscle.

6. Origin of connective tissue cells
6

7. Origin of connective tissue cells
7

8. Components
8
Cells Matrix
Ground
Substance
Fibers

9. 9
 Connective tissue is composed of cells and an
extracellular matrix that binds the cells and
organs, integrating all parts of the body.
 Connective tissue is the most widespread tissue of
the body and can be found in every organ.
 Avariety of cell types are found in connective
tissues.

10. 10

11. 11

12. Connective tissue vs Epithelium:
 Unlike the other tissue types (epithelium,
muscle, and nerve), which consist mainly of
cells, the main component of connective tissue
is the extracellular matrix (ECM).
12

13. 13

14.  Connective tissue that connects, supports, binds, or
separates other tissues or organs, typically having
relatively few cells embedded in an amorphous
matrix, often with or other fibres, and
including cartilaginous, fatty, and elastic tissues.
 The variety of connective tissue types in the body
reflects differences in composition and amount of
the cells, fibers, and ground substance which
together are responsible for the remarkable
structural, functional, and pathologic diversity of
connective tissue.
14

15. Classes of Connective Tissue
15
 Connective tissue proper
 Dense connective tissue
 Loose connective tissue
 Cartilage
 Bone
 Blood

16. 16

17. Protect
Structural support
Bind
Trsansport
Immunity
Connective tissue binds skin to
muscles
17

18. 18

19.  Fibroblasts
 Adipocytes
 Macrophages & the Mononuclear Phagocyte System
 Mast Cells
 Plasma Cells
 Leukocytes
19
Fixed
(permanent
residents)
1. Fibroblasts
2. Adipose (fat) cells
3. Tissue Macrophages**
4. Mast cells**
5. Lymphocytes & Plasma Cells
(differentiated B-cells) **
6. “Leukocytes”**
Free
(transient
residents)
** ( derived from hematopoietic stem cells and involved in immune function and
inflammation. Specifically, neutrophils, eosinophils, & basophils)

20. 20
 Fibroblasts are the key cells in connective tissue
proper. Fibroblasts originate locally from
mesenchymal cells and are permanent residents of
connective tissue.
 Other cells found here, such as macrophages,
plasma cells, and mast cells, originate from
hematopoietic stem cells in bone marrow, circulate
in the blood, and then move into connective tissue
where they function.

21.  The most common cells in connective tissue
proper.
 Produce and maintain most of the
tissue’s extracellular components.
 Fibroblasts synthesize and secrete collagen (the
most abundant protein of the body) and elastin,
which both form large fibers, as well as the
GAGs, proteoglycans, and multiadhesive
glycoproteins that comprise the ground substance.
24

22. C: Connective tissue
arrows: Fibroblasts
22

23. 23

24. 24

25. 28

26. Active vs quiescent cells
26

27. Active vs quiescent cells
27
The inactive form of fibroblasts is called fibrocyte.

28.  Adipocytes, or fat cells, are found in the
connective tissue of many organs.
 These large, mesenchymally derived cells are
specialized for cytoplasmic storage of lipid as
neutral fats, or less commonly for the production
of heat.
 Tissue with a large population of adipocytes,
called adipose connective tissue, serves to
cushion and insulate the skin and other organs.
28

29. Adipocytes
Stored lipids
29

30. White Fat Cell
30

31. 31
 Macrophages & the Mononuclear
Phagocyte System
 Macrophages a large phagocytic cell found in
stationary form in the tissues or as a mobile white
blood cell, especially at sites of infection.
 Size and shape vary considerably, corresponding
to their state of functional activity.

32. Macrophage
ultrastructure
N: nucleus L: lysosomes Nu: nucleolus
36

33. 37
Macrophage

34.  Macrophages arise from monocytes. Monocytes
originate in the bone marrow from where they are
released into the blood stream. They are actively
mobile and leave the blood stream to enter
connective tissues, where they differentiate into
macrophages.
34

35. 35

36. Distribution and main functions of the cells of the
mononuclear phagocyte system
36

37. 37
 Mast Cells
 Mast cells are oval or irregularly shaped cells of
connective tissue, between 7 and 20 μm in
diameter.
 Mast cells filled with basophilic secretory
granules that often obscure the central nucleus.
 Mast cells are components of loose connective
tissues, often located near small blood vessels.

38. 42
BV: blood vessels
Mast cells

39. M: mitochondria
G: cytoplasmic granule
N: nucleus
C: collagen fibers
E: elastic fibers
43
Ultrastructurally mast cells

40. Mast cell
44

41. Function of Mast cells
 Localized release of many bioactive substances
important in the local inflammatory response,
innate immunity, and tissue repair.
 A partial list of molecules released from these
cells’secretory granules includes the following:
Heparin
Histamine
Cytokines
Phospholipid
45

42. Like macrophages, mast cells originate from
progenitor cells in the bone marrow, which circulate
in the blood, cross the wall of small vessels called
venules, and enter connective tissues, where they
differentiate.
42

43. 43
 Plasma Cells
 Plasma cells are lymphocyte-derived, antibody-
producing cells. These relatively large, ovoid
cells have basophilic cytoplasm rich in RER and
a large Golgi apparatus near the nucleus that
may appear pale in routine histologic
preparations.
 The nucleus of the plasma cell is generally
spherical but eccentrically placed.
 Their average life span is only 10-20 days.

44. 44

45. Connective tissue
45

46. 46
 Leukocytes
 leukocyte is a colourless cell which circulates in
the blood and body fluids and is involved in
counteracting foreign substances and disease; a
white (blood) cell.

47. Connective tissue 53

48.  The fibrous components of connective tissue
are elongated structures formed from proteins
that polymerize after secretion from fibroblasts.
 The three main types of fibers are:
 Collagen
 Reticular fibers
 Elastic fibers
48

49. • is a type of fiber found in
connective tissue that provides
strength
Collagen
fiber
49
• is a type of fiber found in
connective tissue that has a netlike
formation and provides support
• is a type of fiber found in
connective tissue that can stretch
and recoil
Reticular
fiber
Elastic
fiber

50.  Collagen and reticular fibers are both formed by
proteins of the collagen family, and elastic fibers
are composed mainly of the protein elastin.

50

51. 51

52. 52

53. 60

54. 54
 Collagen
 The collagens can form various extracellular
fibers, sheets, and networks, all of which
extremely strong and resistant to normal
shearing and tearing forces.
 Collagen is a key element of all connective
tissues, as well as epithelial basement
membranes and the external laminae of muscle
and nerve cells.

55. 55
 Collagen is the most abundant protein in the
human body, representing 30% of its dry weight.
 A family of 28 collagens exists in vertebrates,
numbered in the order they were identified.
They can be categorized according to the
structures formed by their interacting α-chains
subunits:

56. 63

57.  Type I is the most common - 90% of all
collagens are type I. This type is found in bone,
skin, tendon, ligaments, cornea etc.
 Types I, II, III, V and IX are fibrillar, which
means that the protein chains assemble into
fibrils, 10-300nm in diameter.
 Types V & VI form networks in the basal
lamina.
 Type VI helps to anchor basal lamina of skin to
underlying connective tissue. 64

58. C: type I collagen fibrils
arrows: fibroblast
Type I collagen
fibrils
58

59. Collagen synthesis:
59
 Collagen synthesis occurs in many cell types but is
a specialty of fibroblasts.
The Collagen subunit

60. This is a scanning EM
of collagen fibres
60

61. 61

62. 62

63. 63

64. 64
 Reticular fibers
 Reticular fibers found in delicate connective
tissue of many organs, notably in the immune
system.
 Reticular fibers consist mainly of collagen type
III, which forms an extensive network
(reticulum) of thin fibers (diameter 0.5-2 μm)
for the support of many different cells.

65.  Reticular fibers are rarely visible in hematoxylin
and eosin (H&E) preparations but are
characteristically stained black after impregnation
with silver salts and are thus termed argyrophilic.
72

66. 66
 Reticular fibers produced by fibroblasts.
 Reticular fibers occur in the reticular lamina of
basement membranes and typically also
surround adipocytes, smooth muscle and
nerve fibers, and small blood vessels.

67. 67

68. Reticular vs Collagen Fibers
68
Reticular fibers Collagen fibers

69. Reticular vs Collagen Fibers
69
Reticular fibers Collagen fibers

70.  Elastic fibers
Elastin An elastic fiber
 Elastic fibers (or yellow fibers) are bundles of
proteins (elastin) found in extracellular matrix of
connective tissue.
 Elastic fibers produced by fibroblasts and smooth
muscle cells in arteries.
70

71.  Elastic fibers are thinner than the type I collagen
fibers and form rare networks interspersed with
collagen bundles in many organs, particularly
those subject to regular stretching or bending.
 Elastic fibers can stretch up to 1.5 times their
length, and snap back to their original length when
relaxed (e.g. the stroma of the lungs) 78

72. 72

73. Elastic fibers
73

74. Molecular basis of elastic fiber elasticity
74

75. 75

76. Reticular vs Elastic vs Collagen
Fibers
76
Reticular fibers Collagen fibers
Elastic fibers

77. Reticular vs Elastic vs Collagen
Fibers
77
Reticular fibers
Elastic fibers
Collagen fibers

78. 85

79.  Ground substance is an amorphous gel-like
substance in the extracellular space.
 The ground substance of the ECM is a highly
hydrated (with much bound water), transparent,
complex mixture of three major kinds of
macromolecules:
 Glycosaminoglycans (GAGs)
 Proteoglycans
 Multiadhesive glycoproteins 86

80. 80
Ground substance functions:
 Ground substance filling the space between cells
and fibers in connective tissue.
 Ground substance allows diffusion of small
molecules and, because it is viscous,
 acts as both a lubricant and a barrier to the
penetration of invaders.

81. 81

82.  Glycosaminoglycans (GAGs)
 GAGs (also called mucopolysaccharides) are
long polymers of repeating disaccharide units,
89
• binds a considerable amount of water
• it has an important role in allowing molecular
diffusion through connective tissue and in
lubricating various organs and joints.

83.  Proteoglycans
Proteoglycans are GAG's that are covalently
attached to a 'core' protein.
83

84. 84

85.  Classifications used for the various types of
connective tissue typically denote either a
structural characteristic or a major component.
85

86. 94
Classification of connective or supporting tissues

87. 95
CT proper
Binds
Dense CT
Regular
Lig.+Tend.
Irregular
Epidermis
Elastic
Aorta
Loose CT
Adipose
Fat
Areolar
Protects
Reticular
lymph organs
Supporting CT
Protection/ Structure
Cartilage
Elastic
Ear
Hyaline
Ribs
Fibrocartilage
Vertibral discs
Bone
Fluid CT
Transport
Blood
Connective tissue (CT)

88. Connective tissue proper
Loose connective tissue
Dense connective tissue
Supporting connective
tissue
Cartilage
Bone
Fluid connective tissue
Blood
88

89. 89
 Connective Tissue Proper
Connective tissue proper is broadly classified as:
 Loose connective tissue
 Dense connective tissue
 Regular dense connective tissue
 Irregular dense connective tissue

90. 90
 Loose connective tissue
Also called areolar tissue, is common, a layer
beneath the epithelial lining of many organs and
filling the spaces between fibers of muscle and
nerve.
 The loose connective tissue typically contains
cells, fibers, and ground substance in
roughly equal parts.

91. 91
Charastaristics of Loose connective tissue:
 Delicate, flexible, not very resistant to stress.
 Well vascularized.
 All types of connective tissue cells present.
(Majority are fibroblasts and macropahges)
 Collagen, elastic, and reticular fibers present.
 In certain organs (intestine) and in certain disease
conditions, numerous lymphocytes may be present.

92. 100
Loose connective tissue
(areolar tissue)

93. 93

94. (areolar tissue)
94

95. 103
Loose connective tissue
(areolar tissue)

96.  Reticular tissue: a specialized loose connective
tissue with reticular cells that form a fine matrix
of reticular fibers. Provides a structural
framework for hematopoietic organs such as
bone marrow and spleen.
 .
104

97.  Reticular tissue is characterized by
abundant fibers of type III collagen
 This collagen is also known as reticulin
and is produced by modified fibroblasts
called reticular cells.
 Reticular tissues have a high cellular
content.

98. Reticular tissue
98

99. Collagen bundles and Reticular cell processes of the Lymph Node, 200x
99

100. 100
 Dense connective tissue
Dense connective tissue has similar components
as loose connective tissue, but with fewer cells,
mostly fibroblasts, and a clear predominance of
type I collagen fibers over ground substance.
 Less flexible and more resistant to stress
 When collagen bundles are present without
apparent orientation, called dense irregular
connective tissue.
 When oriented in parallel arrays, called dense
regular connective tissue.

101. 101

102. Dense regular connective tissue
102
Dense irregular connective tissue

103. 103

104. Dense regular connective tissue
104
Loose connective tissue

105. 105
 The best examples of dense regular connective
tissue are the very strong and flexible tendons,
cords connecting muscles to bones and
ligaments, bands or sheets that hold together
components of the skeletal system.
 .

106.  Elastic connective tissue: is a modified dense
connective tissue that contains numerous elastic
fibers in addition to collagen fibers, which allows
the tissue to return to its original length after
stretching.
106

107. D: Dense irregular
connective tissue
L: Loose
connective tissue
107

108.  Loose Connective Tissue: The major function of
the loose connective tissue is to serve as a
supporting matrix for the blood vessels,
lymphatic vessels, nerves, muscle fibers,
organs, and the skin.
 Dense Connective Tissue: Dense connective
tissue produces tendon and ligaments by forming
strong, rope-like structures.
108