Components of granulation tissue

The three principal constituents of granulation tissue are endothelial cells, fibroblasts and myofibroblasts, and macrophages (Fig. 3.7.1). Other cells are also present in most cases, the type depending on the aetiology of the granulation tissue formation. For example, abundant inflammatory cells will be found in the granulation tissue at the base of a chronic peptic ulcer.

Fig. 3.7.1 Granulation tissue. (A) Components in granulation. (B) Oedematous connective tissue containing fibroblasts and inflammatory cells.

Endothelial cells grow into the exudate or dead tissue to vascularize it. This process of blood vessel formation is known as angiogenesis or neovascularization. The endothelial cells initially form solid cords, but they soon develop lumina and become capillaries. Indeed, the term granulation tissue comes from the granular appearance imparted by loops and coils of newly formed capillaries. The new endothelial cells are derived from two sources:

sprouting from preexisting vessels adjacent to the injury