Granulation tissue: structure and role in wound healing
Granulation tissue is the soft, red repair tissue of new capillaries (the smallest blood vessels), fibroblasts and immune cells that fills the gap left by injury.
Remember
Granulation tissue is temporary, vessel-rich tissue: new capillaries and fibroblasts fill the gap in a wound before it matures into a scar. The capillaries are why it looks red and bleeds easily.
When tissue is damaged and cannot simply regrow, the body repairs it by organisation, the fibrous repair that ends in a scar. Early in that process, granulation tissue fills the gap left by the injury.
Its defining feature is angiogenesis, the growth of many new small blood vessels. The new capillaries bring oxygen, nutrients and repair cells to the wound. Fibroblasts (the cells that lay down collagen) then build collagen on this base, so the tissue acts as a scaffold, a framework with its own blood supply.
Its colour and its tendency to bleed come from its new capillaries. The blood in the dense network makes it look red, and it bleeds easily when touched. Wounds with tissue loss, separated edges or infection fill with abundant granulation tissue.
Granulation tissue is temporary. It invades the wound space from about day three, after the clot and early inflammation. Over the following weeks the vessels and cells fall in number, and the tissue matures into a stronger, paler scar made of collagen with few cells and few vessels. As the capillaries disappear, an old scar may look white.
Do not confuse granulation tissue with a granuloma. A granuloma is a collection of epithelioid cells (elongated macrophages) that walls off a resistant agent in chronic inflammation. Granulation tissue is the vascular repair bed of a healing wound.
Key facts
- Contents
- new capillaries, fibroblasts and immune cells.
- Defining feature
- angiogenesis, the growth of many new small blood vessels.
- Timing
- the tissue invades the wound space from about day three, after the clot and early inflammation.
- Red and bleeds easily
- both come from the dense network of new capillaries.
- Role
- it fills the gap with a blood-supplied framework on which fibroblasts can build collagen.
- Fate
- it matures into a scar of collagen with few cells and few vessels.
Exam traps
- A tissue of dense, mature collagen does not describe granulation tissue, because that is the scar it matures into; granulation tissue is the earlier, temporary stage.
- A clot is part of the first response to injury, not of granulation tissue: haemostasis (stopping bleeding) happens within seconds to minutes, when a clot and scab form, and granulation tissue appears much later as a repair tissue.
- A cluster of epithelioid macrophages walling off an irritant is a granuloma, not granulation tissue, because granulation tissue is the vascular repair bed of a healing wound.
Read the full notes
Tested in 6 SimpleMed+ questions
Practice it in Pathology, with the answer and a full explanation after every question.
Practice these questions