How does connective tissue differ from the three other tissue types in animal organisms
Muscle, nerve, and epithelial tissue are all characterized by the properties of the cells they contain. The various types of muscle tissue show contractility because of the contractile properties of skeletal, smooth, and cardiac muscle tissue cells. The lining properties afforded by the various types of epithelial tissue are likewise derived from the closely apposed and densely packed layer of epithelial cells. Nerve cells, with their long axonal processes and often branching dendrites, provide the basis for the conduction properties of the tissue.
In connective tissue, an entirely different situation obtains. The properties of the tissue are a function of the extracellular material produced by the cells rather than of the cells per se. The variation in connective tissue types far exceeds that found in each of the other tissue classes.
If we examine these variant connective tissue types, the significance of the extracellular component becomes clear. Vascular tissue is derived from and contains cells, but the bulk of it consists of extracellular fluid such as plasma and lymph. In yellow elastic tissue, the elastic fibers that are responsible for tissue elasticity lie outside the cells. Most striking are the properties of cartilage and bone. In the latter case, a network of bone cells is moored within a matrix of hard, calcareous material that is laid down by the bone cells. Even in fat cells, a large oil globule, carried within a thin rim of cytoplasm, could be viewed as nonliving material lying outside the living portion of the cell.
