Connective and supporting tissue
This tissue group includes many different cell complexes, which, apart from their histologic origin, still have a few similarities of form that relate to the main mechanical function of that tissue. For instance, it is noticeable in connective tissue cells that the intercellular substance (ie, connecting substance between the cells) is highly developed.
In connective tissue, a distinction can be made between the actual connective tissue cells (fixed cells), which make up intercellular substance, and the free cells, which as accompanying cells move around freely in the gaps in the connective tissue (not in supporting tissue) (Fig 2-8).This distinction suggests that the free connective tissue cells and blood should be viewed in conjunction because the main purpose of these free connective tissue cells is to supply the other cells of the body and to defend against toxins, foreign matter, and bacteria. Lymphocytes, for example, are typical free connective tissue cells. Granulocytes, also free connective tissue cells, have their own ameoba-like mobility and phagocytize, which means they can engulf bacteria and ingest them so that the bacteria can be dissolved with the aid of special enzymes.
Connective and supporting tissue can be classified according to the amount and structure of the intercellular substance (Fig 2-9):
Cell-rich connective tissue
- Embryonic connective tissue (mesenchyme)
- Reticular (netlike) connective tissue
- Fatty tissue
Fibrous connective and supporting tissue
- Loose connective tissue -Tight connective tissue
- Elastic connective tissue
Intercellular substance-rich supporting tissue
- Cartilage tissue
- Bone tissue
- Hard dental substances
Cell-rich connective tissue
Embryonic connective tissue is a loose, filling, and elementary tissue in the embryo. The starshaped cells form a loose mesh in which tissue fluid is still deposited instead of intercellular substance.
Reticular connective tissue is also structured as a three-dimensional lattice that holds a fluid ground substance (the lymph) in which numerous lymphocytes are suspended. The reticular connective tissue forms the basic framework of the lymphatic organs (spleen, tonsils, lymph nodes, and bone marrow). Reticulum cells can kill foreign bodies and absorb toxins. The free connective tissue cells are produced in the reticular tissue.
Fatty tissue is a type of reticular connective tissue with a high level of paraplasmic substance, namely fat, which is stored there instead of the fluid ground substance. It is important as an elastic pad, a reserve for calorie-rich fat, a store to maintain the water balance (fat:water = 1:7), and heat protection against sudden cooling.
Fibrous connective and supporting tissue
Loose connective tissue acts as filling tissue because it is found between organs, vessels, and nerves and thus provides cohesion. It is also described as interstitial connective tissue because it fills up the spaces in between. Bundles of tensile, inelastic (collagenous) fibers permeate the loose connective tissue in all directions and provide resistance and stability. However, elastic fibers (elastin) are also found there, so that the tissue has a high level of mobility and returns to its original position after pressure has been placed upon it. Loose connective tissue is a filling and displacement tissue that serves as a water store (eg, in subcutaneous connective tissue).
Tight connective tissue is mainly interspersed with many tensile, inelastic, collagenous fibers to give a highly tensile, not very elastic tissue. It is found as shiny white tissue in the form of a muscular coat (fascia) and as tendinous tissue.
Elastic connective tissue largely comprises elastic fibers (elastin), which make it a highly stretchy tissue that is nevertheless very dimensionally stable. It is found in the walls of blood vessels, as vocal cords in the larynx, and as connecting ligaments attached to the spine.