The connective tissues originate from the mesenchyme, an embryonic tissue formed by elongated cells, the mesenchymal cells. The mesenchyme develops from the middle layer of the embryo, the mesoderm.
Connective tissue is formed by cells and extracellular matrix. Extracellular matrix consist of protein fibers (collagen, elastic, and reticular) and a fluid known as the ground substance.
Connective tissues are found throughout the body but are never exposed to the environment outside the body. Many connective tissues are highly vascular and contain sensory receptors.
The functions of connective tissues include:
1. support and establishing a structure for the body.
2. as a medium for exchange between the blood and tissue.
3. for storage especially in the form of lipids.
4. for the protection from invading microorganisms.
5. transporting fluid and dissolved materials from one region of the body to another.
6. repair.
Cells of the connective tissue :
They usually divided into two groups based on their ability to move within the connective tissue:
1. fixed cells include: fibroblast cells, reticular cells, mesenchymal cells and adipocytes.
2. wandering cells include: macrophages, mast cells, plasma cells, and leukocytes.
Fibroblasts:
* fibroblasts are the most common cell in connective tissue.
* two stages of activity –active (fibroblast) and quiescent (fibrocyte).
* fusiform-shaped fibroblast has an abundant and irregularly branched cytoplasm. Its nucleus is ovoid, large and pale.
* fibrocyte is smaller than fibroblast with spindle-shaped. It has elongated nucleus.
*fibroblasts synthesize proteins that form collagen, elastic, and reticular also produces the ground substance.