Wound healing granulation

(A) Granulation tissue has two major components: cells and proliferating capillaries. The cells are mostly fibroblasts, myofibroblasts, and macrophages. The macrophages are derived from monocytes and macrophages. The fibroblasts and myofibroblasts derive from mesenchymal stem cells, and the capillaries arise from adjacent vessels by division of the lining endothelial cells (detail), in a process termed angiogenesis. Endothelial cells put out cell extensions, called pseudopodia, that grow toward the wound site. Cytoplasmic growth enlarges the pseudopodia, and eventually the cells divide. Vacuoles formed in the daughter cells eventually fuse to create a new lumen. The entire process continues until the sprout encounters another capillary, with which it will connect. At its peak, granulation tissue is the most richly vascularized tissue in the body.
(B) Once repair has been achieved, most of the newly formed capillaries are obliterated and then reabsorbed, leaving a pale avascular scar.
(C) A photomicrograph of granulation tissue shows thin-walled vessels embedded in a loose connective tissue matrix containing mesenchymal cells and occasional inflammatory cells.