Connective Tissue

Learning objectives:

• Know that cells, fibers and ground substance constitute connective tissue.
• Be able to describe the relationship of these constituents, their structures and functions.
• Learn the distribution of collagen types (Types I, II, III and IV) in the connective tissue types.

Connective tissue is comprised of cells, formed fibers and amorphous extracellular matrix (ground substance). Both the fibers and ground substance are secreted by the connective tissue cells that are interspersed and embedded in the matrix. Functions of the connective tissue are manifold. They include support and binding together of the other tissues; providing a medium for the passage of metabolites; serving as a storage site for lipids, water and electrolytes; aiding in protection against infection by an inflammatory reaction mediated by cells that have migrated into the connective tissue from the blood; and repair by the formation of scar tissue.

There are four main types or subdivisions of connective tissues:

1. Connective tissue proper
2. Cartilage
3. Bone and dentin
4. Blood and lymph

Major differences among the various types of connective tissues are due in large part to the nature of their intercellular substance; thus, blood is characterized by its fluid intercellular substance, the plasma, while bone is characterized by the impregnation of its matrix with calcium salts.

Connective tissues are derived from the embryonic connective tissue or mesenchyme. Mesenchyme is derived primarily from the mesodermal germ layer of the developing embryo, but the ectodermal neural crest is known to give rise to some mesenchymal cells (ecto-mesenchyme). See examples in subsequent lab (Cartilage, Bone and their development).

A Classification of Non-Specialized Connective Tissue

1. Loose (Areolar) Connective Tissue

1.1 Areolar connective tissue - subcutaneous tissue, lamina propria.
1.2 Reticular connective tissue - forms a supporting framework for spleen, lymph nodes, bone marrow, liver, glands, and striated muscle fibers.
1.3 Adipose connective tissue - a modification of reticular connective tissue, characterized by an extensive intracellular accumulation of lipid droplets.

2. Dense, Irregular Connective Tissue

2.1 Predominantly collagenous - dermis, capsule of spleen and other organs, such as the prostate gland.
2.2 Predominantly elastic - for example, the elastic membrane of large arteries.
3. Dense, Regular Connective Tissue

3.1 Collagenous - tendons, most ligaments, cornea
3.2 Elastic - elastic ligaments (ligamentum nuchae flavate and interspinous ligaments), true vocal cords
4. Mesenchyme (Embryonic Connective Tissue)

Primitive connective tissue that contains precursors for connective tissue as well as other tissue types.

Lab Activities

1. Loose (Areolar) Connective Tissue
2. Reticular Connective Tissue
3. Adipose Connective Tissue
4. Dense, Irregularly Arranged Connective Tissue
5. Dense, Regularly Arranged Connective Tissue
6. Electron Micrographs
7. Questions
8. Answers