Ground substance

CONNECTIVE TISSUES

The tissue derives its names from its function in connecting or binding cells and tissues. Connective tissues are very heterogeneous in structure and function, however all have:

• common origin – from mesenchyme ( mesenchymal stromal cell – Fig.1)

• common in structure – extracellular matrix plays a major role in the functioning of the tissue and is the dominant component of the tissue; t he dominance of the extracellular matrix is a special feature that distinguishes connective tissue from the other tissues of the body.

Connective tissue is composed of:

• cells

• extracellular matrix.

The extracellular matrix is composed of:

• protein fibers (collagen, reticular, elastic);

• amorphous ground substance;

• tissue fluid.

Functions of connective tissue are:

• structural support ( maintenance of anatomical form of organs and organ systems (capsules of organs, stroma, tendons, ligaments, cartilage, bone).

• metabolic functions; t he role of connective tissue in nutrition is a result of its close association with blood vessels. The connective tissue matrix serves as the medium through which nutrients and metabolic wastes are exchanged between cells and their blood supply.

• defending functions; the role of connective tissue in defending the organism is related to its content of phagocytic and immunocompetent cells as well as cells that produce pharmacologically active substances that are important in modulating inflammation (the site of inflammation and immune reactions)

Classification. There are several types of connective tissue. The names given to the different types denote either the component that predominant in the tissue or a structural characteristic of the tissue:

• I. Fibrous connective tissues (proper);

• II. Special connective tissues (adipose, reticular, pigment and mucous);

• III. Skeletal connective tissues (cartilages and bones).

CONNECTIVE TISSUE PROPER

Ground substance

The amorphous intercellular ground substance, a complex mixture of glycoproteins and proteoglycans that participate in binding cells to the fibers of connective tissues, is colorless, transparent, and homogeneous. It fills the space between cells and fibers of the connective tissue; it is viscous and acts as a lubricant and also as a barrier to the penetration of the tissues by foreign particles.

The ground substance is formed mainly by 2 classes of components:

· glycosaminoglycans (GAG);

· structural glycoproteins.

Glycosaminoglycans (GAGs) are linear polysaccharides formed by characteristic repeating disaccharide units. With the exception of hyaluronic acid, these linear chains are bound covalently to a protein core, forming a proteoglycan molecule.

This is a 3-dimensional structure that can be pictured as a test tube brush, with the wire stem representing the protein core and the bristles representing the glycosaminoglycans (Fig.2).

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