Answer
Connective tissue is composed of cell and matrix--the matrix includes ground substance and fibers of three kinds.
A. The cells of mature connective tissues are many and varied: they include fibroblasts, macrophages, mast cells, plasma cells, adipocytes and blood cells. Chondrocyes, and osteocytes are really specialized types of fibroblasts/fibrocytes.
1. Fibroblasts are usually large flat cells which may have branches. They are common to all connective tissues . Their major function is to secrete fibers and ground substance but the may be modified for other functions such as storing fat( adipocytes).
Chondroblasts are a type of fibroblast which are found in spaces in cartilage called lacunae
2.Macrophages-these are phagocytic cells that derive from monocytes of the blood. Macrophages reside in fixed tissue locations -- as in the alveoli of lungs-- or they may wander rough tissues to the sites of infection to fight bacteria. Macrophages are phagocytes that ingest bacteria, debris, and dead cells.
3. Plasma cells derive from B lymphocytes; they are found all over the body; they occur in many types of connective tissues in different locations as in GI tract, the respiratory tract, and in red bone marrow. Their function is to produce antibodies that neutralize antigens.
4. Mast cells, which are found in connective tissues near blood vessels,
have two main functions: first, they secrete heparin, which inhibits coagulation ; second, they produce antibodies to neutralize antigens;mast cells are also bacteriocidal.
5. Adipocytes are fibroblasts modified to store fat ( triglycerides) . They serve to cushion and protect some organs , but they also supply insulation and serve as reserves of energy(heat) that are important in maintaining the temperature homeostasis of the body .
6. Leucocytes . These are white blood cells. They migrate from the blood and accumulate at
sites of infection in connective tissues: neutrophils are phagocytic at sites of infection, and eosinophils are attracted to areas of parasitic invasion and allergic reactions.
Work Step by Step
Matrix:
1. Ground substance:
Fibers and cells exist or are surrounded by ground substance , the consistency of which varies among the different types of connective tissues. Ground substance may be watery (fluid) as in blood or lymph, viscous, gelatinous or solid --as in bone. In addition to water ground substances has several important complex organic molecules , ions and salts. The complex molecules also called glycosaminoglycans(GAGS) are compounds of proteins and certain polysaccharides , the latter conferring specific capabilities on the ground substance. Thus hyaluronic acid protects and lubricates, chondroitin sulfate is supportive and adhesive ( as in walls of blood vessels, bone, skin and cartilage), Cells, fibers and ground substance are also linked together by other ground substance substances like the adhesive protein, fibronectin
FIBRES;
Three types of fibers are embedded in connective tissue ground substance. They vary in size regularity , branching and composition.
Collagen fibers predominate; They may be of large diameter , unbranching and laid down in almost parallel lines with rows of fibroblasts in between. In irregular connective tissue the rows are less regular and the cells are not disposed in regular rows.These large collagen fibers are found in dense regular and dense irregular connective tissues. These large collagen fibers resist pulling stresses and give great tensile strength to tendons, ligaments , cartilage and bone.
The second type of connective tissue fiber is elastic fibers.They are made up of a complex of a protein called elastin and fibrillin, which is a glycoprotein.These fibers are smaller in diameter than regular collagen fibers, and in addition they branch to for a network . Elastin fibers are plentiful in skin, walls of blood vessels, and in the connective tissue of the lungs. In these tissues, the capacity to expand and return to original dimensions is integral to their functions. Elastic fibers confers this ability because this tissue has the quality of elasticity which permits extension and recovery in length without damage or rupture
