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.
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.
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.
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
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
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
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
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.
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
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.
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.
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.
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
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:
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
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.
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
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.
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.
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.
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.
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.
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
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