BIOLOGY Volume 1 - A Guide to General Biology - 2004

6. HISTOLOGY

6.4. Animal Connective Tissue

Connective Tissue is the primary supporting tissue of the body. It includes the Tissues that form the Skeleton—bone and Cartilage—and also serves to bind other tissues together. Connective tissue envelops various Organs from the outside, encasing them as if in sacs and separating them from one another to prevent Interference with neighboring Functions. Additionally, it surrounds Blood Vessels and nerves where they enter and exit organs. Connective tissue is a complex Structure composed of various Cells. It contains several types of fibres produced by these cells, which are embedded in a liquid or semi-liquid ground substance, or matrix.

Connective tissue cells are typically located quite far apart from one another. In certain PARTS OF THE body, such as the dermal layer of the Skin, there are extensive networks of Blood Vessels, but their primary function is to supply oxygen and nutrients not to the connective tissue itself, but to other structures, such as the epithelium. There are several types of connective tissue, as listed in Table 6.3.

In addition to connecting and compartmentalizing various structures, this tissue performs many other functions: it protects the body against mechanical damage and bacterial invasion (Cytology/practical/43.html">Areolar connective tissue), provides thermal insulation (adipose tissue), serves a supportive role (cartilage and bone), and produces Blood Cells.

Class="center">Table 6.3. Types of Connective Tissue

6.4.1. Areolar, Fibrous Connective, and Adipose Tissues

Areolar tissue is shown in Fig. 6.21, Fibrous connective tissue in Figs. 6.22 and 6.23, and adipose tissue in Fig. 6.24.

Fig. 6.21. Loose areolar connective tissue, with widely scattered cells. In addition to the cells labeled here, this tissue contains fat droplets (see Fig. 6.24), mast cells that respond to mechanical injury, and antibody-producing cells (plasma cells). Areolar tissue surrounds all body organs; its fibres are randomly distributed throughout the matrix.

Fig. 6.22. White fibrous tissue. It consists primarily of parallel bundles of Collagen fibres. This is a strong and flexible, yet inelastic tissue. Tendons, which attach skeletal Muscles to bones, consist almost entirely of white fibres. White fibrous tissue is also found in ligaments, the sclera, the cornea, and wherever structural strength is required.

Fig. 6.23. Yellow elastic tissue is formed by a network of elastic fibres composed of the protein Elastin. These fibres are typically present in structures that require elasticity—such as the walls of Arteries and the alveoli of the Lungs, as well as in ligaments.

Fig. 6.24. Adipose tissue. This tissue is found in the dermis and also surrounds the Kidneys and Heart. It serves as the body's energy reservoir, a Shock absorber, and protection against heat loss.