Lec.3 Biology
HistologyConnective tissue
Connective tissue is the most abundant and widely distributed tissue in the body . While some connective tissues are specialized ( bone , blood), all organs have some amount of connective tissue in them which hold their parenchyma together.
Connective Tissue is characterized by:
Binding and supporting the organs.It is vascular except the cartilage.
It is derived from mesoderm layer.
It consists of cell immersed in large amount of intercellular substance, which is formed by cells.
Can replicate (healing and repair)
Functions of connective tissues :
• Enclosing and separating organs• Connecting tissues to one another (ligaments and tendons)
• Supporting and moving ( Joints and cartilage)
• Storing (adipose tissue and bones)
• Cushioning and insulating (adipose tissues)
• Transport and protection (blood)
Components of Connective Tissue
Extracellular matrix: composed of ground substance and fibers.
Connective tissue cells.
The composition and structure of extracellular matrix determine function and characteristic of connective tissue.
(Basic elements in a typical connective tissue)
Ground SubstanceGround substance: is a hydrated colorless and transparent, amorphous material. It is found in all cavities and clefts between the fibers and cells of connective tissues. The ground substance may be viscous (as in blood), semisolid (as in cartilage), or solid (as in bone). Ground substance supports cells, binds them together, stores water ,and provides a medium through which substances are exchanged. It primarily consists of protein and carbohydrate molecules and variable amounts of water. The protein and carbohydrates are mainly present in form of proteoglycans and glycoproteins (Proteoglycan = Protein core + glycosaminoglycan. Glycoprotein= Protein + oligosaccharide ). Also present in the ground substance are adhesion proteins , which are responsible for linking components of the ground substance to one another and to the surfaces of cells.
Fibers:
There are three types of connective tissue fibers:Collagen fibers (white fiber):
They are the most numerous and strongest fibers in the body . Collagen fibers are made of protein called "collagen" and appear as fine clear threads in fresh preparations. Thus, they are often called “white fibers. They are formed by fibroblasts. These fibers are straight or wavy, un branched, they always run parallel to each other forming bundles, which branched and anastomose. Found in abundance in bone , cartilage, tendon & ligament. They function in (1) providing a structural framework and in (2) providing strength.
Types of Collagen fibers:
•Type 1- bones & tendons
•Type 2- cartilage (hyaline & elastic)
•Type 3- reticular fibers
•Type 4- basement membrane
•Type 5- blood vessels
Elastic fibers
Elastic fibers are made of the protein elastin and appear yellow in fresh preparations. Thus, they are often called “yellow fibers. They are generally formed by fibroblasts. Elastic fibers are smaller in diameter than collagen fibers, branch to form a network within the tissue, found in ligaments and vocal cords. They function in allowing the tissue to stretch and recoil.