Granulation tissue
{{Short description|New tissue that forms on a wound's surface}}
{{distinguish|Granuloma}}
{{Redirect|Proud flesh||Proud Flesh (disambiguation)}}
{{more citations needed|date=May 2020}}
Granulation tissue is new connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process.{{cite web|url=http://www.memidex.com/granulation-tissue|work=Memidex|title=Granulation Tissue Definition|access-date=25 October 2014|archive-date=16 November 2018|archive-url=https://web.archive.org/web/20181116035707/http://www.memidex.com/granulation-tissue|url-status=live}} Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size. Examples of granulation tissue can be seen in pyogenic granulomas and pulp polyps. Its histological appearance is characterized by proliferation of fibroblasts and thin-walled, delicate capillaries (angiogenesis), and infiltrated inflammatory cells in a loose extracellular matrix.
Appearance
File: Finger with granulation tissue.jpg
During the migratory phase of wound healing, granulation tissue is:
- light red or dark pink, being perfused with new capillary loops or "buds";
- soft to the touch;
- moist;
- bumpy (granular) in appearance, due to punctate hemorrhages;
- pulsatile on palpation;
- painless when healthy;{{cite book|last=Bhat|first=Sriram|title=Srb's Manual of Surgery, 4e|year=2013|publisher=Jaypee Brother Medical Pub|isbn=9789350259443|page=18}}
Structure
Granulation tissue is composed of tissue matrix supporting a variety of cell types,{{cite journal |last1=Olczyk |first1=Pawel |last2=Mencner |first2=Łukasz |last3=Komosinska-Vassev |first3=Katarzyna |title=The Role of the Extracellular Matrix Components in Cutaneous Wound Healing |journal=BioMed Research International |date=2014 |volume=2014 |pages=1–8 |doi=10.1155/2014/747584|doi-access=free |pmid=24772435 }} most of which can be associated with one of the following functions:
- formation of extracellular matrix;
- operation of the immune system;
- vascularisation;
An excess of granulation tissue (caro luxurians) is informally referred to as hypergranulation or "proud flesh".[http://compepid.tuskegee.edu/syllabi/pathobiology/pathology/genpath/chapter9.html Healing and Repair] {{Webarchive|url=https://web.archive.org/web/20100927065700/http://compepid.tuskegee.edu/syllabi/pathobiology/pathology/genpath/chapter9.html |date=2010-09-27 }} Chapter 9 from an "Introduction to Pathology" on a Tuskegee University website
=Extracellular matrix=
{{Main article|Extracellular matrix}}
File:Histopathology of biopsy site at 11 days, high magnification.jpg
The extracellular matrix of granulation tissue is created and modified by fibroblasts.{{cite journal |last1=Midwood |first1=Kim S. |last2=Williams |first2=Leyla Valenick |last3=Schwarzbauer |first3=Jean E. |title=Tissue repair and the dynamics of the extracellular matrix |journal=The International Journal of Biochemistry & Cell Biology |date=June 2004 |volume=36 |issue=6 |pages=1031–1037 |doi=10.1016/j.biocel.2003.12.003|pmid=15094118 }} Initially, it consists of a network of type-III collagen, a weaker form of the structural protein that can be produced rapidly. This is later replaced by the stronger, long-stranded type-I collagen, as evidenced in scar tissue.
=Immunity=
The main immune cells active in the tissue are macrophages and neutrophils, although other leukocytes are also present.{{cite journal |last1=Sindrilaru |first1=A |last2=Scharffetter-Kochanek |first2=K |title=Disclosure of the Culprits: Macrophages-Versatile Regulators of Wound Healing. |journal=Advances in Wound Care |date=September 2013 |volume=2 |issue=7 |pages=357–368 |doi=10.1089/wound.2012.0407 |pmid=24587973|pmc=3842885 }} These work to phagocytize old or damaged tissue, and protect the healing tissue from pathogenic infection. This is necessary both to aid the healing process and to protect against invading pathogens, as the wound often does not have an effective skin barrier to act as a first line of defense.
=Vascularization=
It is necessary for a network of blood vessels to be established as soon as possible to provide the growing tissue with nutrients, to take away cellular wastes, and transport new leukocytes to the area. Fibroblasts, the main cells that deposit granulation tissue, depend on oxygen to proliferate and lay down the new extracellular matrix.{{cite journal |last1=Cialdai |first1=Francesca |last2=Risaliti |first2=Chiara |last3=Monici |first3=Monica |title=Role of fibroblasts in wound healing and tissue remodeling on Earth and in space |journal=Frontiers in Bioengineering and Biotechnology |date=4 October 2022 |volume=10 |doi=10.3389/fbioe.2022.958381|doi-access=free |pmid=36267456 |pmc=9578548 }}
In vascularisation, also called angiogenesis, endothelial cells quickly grow into the tissue from older, intact blood vessels.{{cite journal |last1=Tonnesen |first1=Marcia G. |last2=Feng |first2=Xiaodong |last3=Clark |first3=Richard A.F. |title=Angiogenesis in Wound Healing |journal=Journal of Investigative Dermatology Symposium Proceedings |date=December 2000 |volume=5 |issue=1 |pages=40–46 |doi=10.1046/j.1087-0024.2000.00014.x|pmid=11147674 }} These branch out in a systematic way, forming anastomoses with other vessels.
File:Wound healing phases.png, with substantial variation depending on wound size and healing conditions. Granulation tissue formation is seen in green box at days to weeks.]]
References
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{{Wound healing}}
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