Download Connective Tissue

CONNECTIVE TISSUE
BY
ADEKEYE ADESHINA
2015
CONNECTIVE TISSUE
Outline:
• Definition
• Formation/components of CT
• Function of CT
• Extracellular matrix
• Cells of CT
• Classification of CT
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Connective tissue is formed primarily of
Extracellular matrix (ground substance and protein fibers)
Connective tissue cells
ORIGIN
The CT originate from the mesenchyme, an embryonic tissue
formed by elongated undifferentiated cells, the mesenchymal
cells
Functions
Connective tissue supports organs and cells
Acts as a medium for exchange of nutrients and wastes
between the blood and tissues
Protects against microorganisms
Repairs damaged tissues
Stores fat.
EXTRACELLULAR MATRIX (ECM)
It is the major constituent of Connective tissue
It consist of different combinations of protein fibers
(collagen, reticular, and elastic) and ground substance.
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Ground substance is a colorless, highly hydrophilic,
transparent, gel-like material in which the cells and
fibers of connective tissue are embedded.
It is a complex mixture of glycosaminoglycans,
proteoglycans, and glycoproteins
Ground substance serves as
lubricant
Prevent invasion of tissues by foreign agents, and resists
forces of compression.
FIBERS:
• are long, slender protein polymers present in
different proportions in different types of
connective tissue.
• predominantly composed of collagen,
constitute tendons, aponeuroses, capsules of
organs and membranes that envelop the
central nervous system (meninges)
• Collagen and reticular fibers are both formed
by the protein collagen
• Elastic fibers are composed mainly of the
protein elastin.
• These fibers are distributed unequally among
the types of connective tissue.
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• 1. Collagen fibers : there are at least 25
different types of collagen, the most common
collagen types in connective tissue proper are
type I and type III collagen, both consisting
of many closely packed tropocollagen fibrils.
• Chief examples among its various types are present in
the skin, bone, cartilage, smooth muscle, and basal
lamina.
• Collagen is the most abundant protein in the
human body, representing 30% of its dry
weight.
• Collagens that Form Long Fibrils
I-Skin, tendon, bone, dentin
Function:Resistance to tension
II-Cartilage, vitreous body
Function:Resistance to pressure
III-Skin, muscle, blood vessels
Function:Structural maintenance in expansible organs
Others include V and XI (Cartilage)
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Fibril-associated collagens
IX, XII and XIV
Examples include Cartilage, vitreous body, Embryonic tendon,
skin, Fetal skin and tendon
Collagen that forms anchoring fibrils
VII
Example include Epithelia
Collagen that forms networks
Example include all basement membranes
Collagen fibers have great tensile strength,
which imparts both flexibility and strength
to tissues containing them.
Bone, skin, cartilage, tendon, and many
other structures of the body contain
collagen fibers.
The levels of organization in collagen
fibers
NOTE: Collagen is the most abundant structural protein of the ECM
• 2. Reticular fibers are extremely thin (0.5–2.0 m) in
diameter and are composed primarily of type III
collagen.
• they have higher carbohydrate content than other
collagen fibers.
• 3. Elastic fibers are coiled branching fibers 0.2 to 1.0
m in diameter that sometimes form loose networks.
These fibers may be stretched up to 150% of their
resting length.
They are composed of elastin and microfibrils of
fibrillin
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.Cells of Connective Tissue
Some originate locally and remain in the connective tissue
(fixed cells)
Fixed connective tissue cells include
fibroblasts
Pericytes
adipose cells
mast cells
fixed macrophages.
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whereas others originate elsewhere (HSC in Bone marrow)
and remain only temporarily in connective tissue (transient
cells)
Transient connective tissue cells include
Certain macrophages,
Lymphocytes
Plasma cells
Neutrophils
Eosinophils
Basophils
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4 Major cell components of the connective tissues
Fibroblast : originate locally from undifferentiated
mesenchymal cells
Macrophage
Mast cell
Plasma cell
• Note: MMP originate from hematopoietic stem
cells in bone marrow, circulate in the blood
and then move into connective tissue where
they remain and execute their functions
Origin of connective tissue cells. Cells arising from undifferentiated mesenchymal cells are
formed in connective tissue and remain there
Lineages of connective tissue cells
A. Fixed Cells of Connective Tissue
• 1. FIBROBLASTS arise from mesenchymal cells
and are the predominant cells in connective tissue
proper.
• It originate locally from undifferentiated
mesenchymal cells and spend all their life in this
tissue
• They often possess an oval nucleus with two or
more nucleoli.
• They may differentiate into other cell types under
certain conditions.
• Fibroblasts synthesize collagen, elastin,
glycosaminoglycans, proteoglycans and
multiadhesive glycoproteins.
• Fibroblasts are the most common cells in
connective tissue and are responsible for the
synthesis of extracellular matrix components.
• Two stages of activity—active and quiescent
• Active fibroblasts are spindle shaped (fusiform) and
contain well-developed rough endoplasmic reticulum
(RER) and many Golgi complexes.
• Myosin is located throughout the cytoplasm, and
actin and -actinin are located at the cell periphery.
• Clinical consideration: Fibroblasts undergo mitosis
only during wound healing.
•The active fibroblast has an
abundant and irregularly branched
cytoplasm.
•The active fibroblast has an
abundant
and irregularly branched
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cytoplasm.
•Its nucleus is ovoid, large, and pale
staining, with fine chromatin and a
prominent nucleolus.
• The cytoplasm is rich in rough
endoplasmic reticulum, and the
Golgi complex is well developed
A connective tissue layer (dermis) shows
several fibroblasts H&E stain
•Quiescent fibroblasts are
elongated cells with thin
cytoplasmic extensions
and condensed chromatin.
•Pararosaniline–toluidine
blue (PT) stain
•Active (left) and quiescent (right)
fibroblasts.
•External morphological
characteristics and ultrastructure
of each cell are shown.
•Fibroblasts that are actively
engaged in synthesis are richer in
mitochondria, lipid droplets, Golgi
complex, and rough endoplasmic
reticulum than are quiescent
fibroblasts (fibrocytes)
• 2. PERICYTES are derived from embryonic mesenchymal
cells and may retain a pluripotential role.
• . They possess characteristics of endothelial cells as well as
smooth muscle cells because they contain actin, myosin, and
tropomyosin, suggesting that they may function in
contraction.
• . They are located mostly along capillaries and may function
as contractile cells that modify capillary blood flow.
• . During blood vessel formation and repair, they may
differentiate into smooth muscle cells as well as endothelial
cells.
• In response to injury, pericytes may give rise to
endothelial cells, fibroblasts and smooth muscle cells of
blood vessel walls.
3. ADIPOSE CELLS (adipocytes)
• Arise from mesenchymal cells and perhaps from
fibroblasts
• They do not normally undergo cell division because
they are fully differentiated cells.
• However, they do increase in number in early
neonatal life.
• They are surrounded by a basal lamina and are
responsible for the synthesis, storage and release of
fat.
TYPES OF ADIPOSE CELLS
• a. Unilocular adipose cells (white adipose tissue)
contain a single large fat droplet.
• (1) These cells have plasmalemma receptors for insulin,
growth hormone, norepinephrine and glucocorticoids to
control the uptake and release of free fatty acids and
triglycerides.
• (2) They are surrounded by a basal lamina and are
responsible for the synthesis, storage and release of
fat.
• b. Multilocular adipose cells (brown adipose tissue)
are smaller than unilocular adipose cells and the fat is
stored as many small fat droplets, and thus the spherical
nucleus is centrally located.
4. MAST CELLs
arise from myeloid stem cells in bone marrow and
usually reside near small blood vessels.
• They possess a central spherical nucleus; their
cytoplasm is filled with coarse, deeply stained
metachromatic granules
• Their surfaces are folded, and in electron
micrographs they have a well-developed Golgi
complex, scant RER, and many dense lamellated
granules. Two populations of mast cells exist.
• Mast cells function in the localized release of
many bioactive substances with roles in the
inflammatory response, innate immunity, and
tissue repair
• Connective tissue mast cells possess secretory
granules containing heparin.
• The other population, the smaller mucosal mast cells
whose secretory granules contain chondroitin
sulfate, is located in the mucosa of the alimentary
canal and of the respiratory tract.
Simplified representation of the connective tissue cell lineage derived from
the multipotential embryonic mesenchyme cell
• B. Transient Cells of Connective Tissue
• 1. Macrophages are the principal phagocytosing cells of
connective tissue.
• They are responsible for removing large particulate matter and
assisting in the immune response.
• They also secrete substances that function in wound
healing..
• MACROPHAGES originate in the bone marrow as
monocytes, circulate in the bloodstream, then migrate into the
connective tissue, where they mature into functional
macrophages.
Macrophages have specific name in certain organs
for example, they are called Kupffer cells in the
liver, Osteoclast in bone and microglia cell in the
CNS.
Macrophages in the connective tissue have the
following features:
• They contain abundant lysosomes required for the
breakdown of phagocytic materials.
• Active macrophages have numerous phagocytic
vesicles (or phagosomes) for the transient storage
of ingested materials.
• The nucleus has an irregular outline.
• 2. Lymphoid cells
• Arise from lymphoid stem cells during hemopoiesis
• They are located throughout the body in the subepithelial
connective tissue and accumulate in the respiratory system,
gastrointestinal tract and elsewhere in areas of chronic
inflammation.
• a. T lymphocytes (T cells) initiate the cell-mediated
immune response.
• b. B lymphocytes (B cells), following activation by an
antigen, differentiate into plasma cells, which function in the
humoral immune response.
• c. Natural killer cells (NK cells) lack the surface
determinants characteristic of T and B lymphocytes but may
display cytotoxic activity against tumor cells
• 3. Plasma cells
• are antibody-manufacturing cells that arise from activated B
lymphocytes and are responsible for humoral immunity.
• a. These ovoid cells contain an eccentric nucleus possessing
clumps of heterochromatin, which appear to be arranged in a
wheel-spoke fashion.
• b. Their cytoplasm is deeply basophilic because of an
abundance of RER.
• c. A prominent area adjacent to the nucleus appears pale and
contains the Golgi complex (negative Golgi image).
• d. They are most abundant at wound entry sites or in areas of
chronic inflammation..
• 4. Granulocytes
• are white blood cells that possess cytoplasmic
granules and arise from myeloid stem cells during
hemopoiesis.
• At sites of inflammation, they leave the bloodstream
and enter the loose connective tissue, where they
perform their specific functions .
• a. Neutrophils phagocytose, kill, and digest
bacteria at sites of acute inflammation.
• b. Eosinophils bind to antigen–antibody
complexes on the surface of parasites
(e.g.,helminths) and then release cytotoxins that
damage the parasites.
• They are most prevalent at sites of chronic or
allergic inflammation.
• c. Basophils are similar to mast cells
CLASSIFICATION OF CONNECTIVE TISSUE
• Based on the proportion of cells to fibers &
on the arrangement and type of fibers
• Embryonic connective tissue
• Connective tissue proper
• Specialized connective tissue.
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A. Embryonic connective tissue
It is a loose tissue formed during early embryonic
development
1. Mucous tissue (Wharton jelly) is a loose connective
tissue that is the main constituent of the umbilical cord
and fetal tissues.
has an abundance of ground substance composed chiefly of
hyaluronic acid
It consists of a jellylike matrix with very few collagen fibers
in which LARGE STELLATE FIBROBLASTS are scatterly
embedded.
2. Mesenchymal tissue is found only in embryos.
It consists of a gel-like amorphous matrix containing
only a few scattered reticular fibers, in which star-shaped,
pale-staining mesenchymal cells are embedded
Mucous tissue.
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B. Connective tissue proper (Adult Connective
Tissue)
It has a considerable structural diversity because the
proportion of cells to fibers and of ground substances
varies from tissue to tissue.
This variable cell to ECM ratio is the basis for the
subclassification of adult connective tissue into two
type of connective tissue proper.
1. Loose (or areolar) connective
2. Dense connective tissue
• Loose connective tissue
• contains more cells than collagen fibers
• generally found in the mucosa and
submucosa of various organs and
surrounding blood vessels, nerves and
muscles, papillary layer of the dermis,
hypodermis, linings of the peritoneal, pleural
cavities, glands, mucous membranes
supporting the epithelial cells.
• Well vascularized, flexible, and not very
resistant to stress.
• It usually supports epithelial tissue
• It is more abundant than dense connective
tissue
• The most numerous cells are fibroblasts and
macrophages, but other types of connective
tissue cells are also present.
• Collagen, elastic, and reticular fibers also
appear in this tissue.
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Dense connective tissues
contains more of collagen fibers than cells.
is adapted to offer resistance and protection.
When the collagen fibers are preferentially
oriented as in tendons, ligaments and the
cornea, the tissue is called Dense regular
connective tissue.
• When the collagen fibers are randomly
oriented- as in the dermis of the skin, the tissue
is called dense irregular
longitudinal section of dense regular
connective tissue of a tendon
Loose and dense irregular connective
tissue within the esophagus
Section of loose connective tissue.
Many fibroblast nuclei are interspersed
with irregularly distributed collagen fiber
Section of immature dense irregular
collagen tissue.
Dense irregular connective tissue
from human dermis contains thick
bundles of collagen fibers, fibroblast
nuclei
• NOTE:
• Reticular and elastic fibers predominate in irregular connective
tissue.
• Reticular connective tissue
• contains reticular fibers, which form the stroma of organs of
the lymphoid-immune system (e.g lymph nodes and spleen), the
hematopoietic bone marrow and the liver.
Function
• Provides a delicate meshwork to allow passage of cells and
fluid.
• Elastic connective tissue
• contains irregularly arranged elastic fibers in ligaments of the
vertebral column.
Function
• Provides elasticity.
Light micrograph of reticular
tissue (silver stain)
• C. The Special connective tissue
• comprises types of connective tissue with
special properties not observed in the
embryonic or adult connective tissue proper.
There are four types of special connective
tissue
1. Adipose tissue
2. Cartilage
3. Bone
4. Hematopoietic tissue (bone marrow)
• Adipose tissue has more cells (adipose cell or
adipocytes) than collagen fibers and ground
substance.
• This type of connective is the most significant
energy storage site of the body.
• The hematopoietic tissue is found in the
marrow of selected bones
• Esssentially, cartilage and bone are dense
connective tissues with specialized cells and
ground substance.
• An important difference is that cartilage has a
noncalcified ECM whereas the ECM of bone
are calcified
• Assignment
• List the cell of mononuclear phagocyte system
and their function