Connective Tissue

Connective Tissue
Structure
Connective tissue is formed primarily of extracellular matrix,
consisting of ground substance, extracellular fluid, and fibers, in
which various connective tissue cells are embedded.
Function
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, and stores
fat.
Extracellular Matrix.
The extracellular matrix provides a medium for the transfer of
nutrients and waste materials between connective tissue cells and the
bloodstream.
Ground substance
Ground substance is a colorless, 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 (see Chapter 4 for details on these components).
• Ground substance is a lubricant, helps prevent invasion of tissues
by foreign agents, and resists forces of compression.
Fibers
(collagen, reticular, and elastic) are long, slender protein polymers
present in different proportions in different types of connective
tissue.
Collagen fibers.
• There are at least 19 molecular 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. The average diameter of type I collagen fibrils is 75
nanometers (nm)
o Collagen fibers are produced in a two-stage process involving
intracellular events (within fibroblasts) and extracellular events.
o Collagen fibers have great tensile strength, which imparts both
flexibility and strength to tissues containing them.
o c. Bone, skin, cartilage, tendon, and many other structures of the
body contain collagen fibers.
Reticular fibers
• These are extremely thin [0.5-2.0 micrometers (um) in diameter] and
are composed primarily of type III collagen; they have a higher
carbohydrate content than other collagen fibers.
o Type III collagen fibers constitute the architectural framework of
certain organs and glands.
o Because of their high carbohydrate content, they stain black with
silver salts.
Elastic fibers
• These are coiled, branching fibers 0.2-1.0 um in diameter that
sometimes form loose networks.
o These fibers may be stretched up to 150% of their resting length.
o They are composed of microfibrils of elastin and fibrillin embedded
in amorphous elastin (see Chapter 4 III B).
o Elastic fibers require special staining in order to be observed by
light microscopy.