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Granulation tissue is new
During the migratory phase of
Healing and Repair
Chapter 9 from an "Introduction to Pathology" on a Tuskegee University website
The extracellular matrix of granulation tissue is created and modified by fibroblasts. 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
connective tissue
Connective tissue is one of the four primary types of animal
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to mov ...
and microscopic blood vessels that form on the surfaces of a wound during the healing process. 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 new thin-walled, delicate capillaries (angiogenesis), infiltrated inflammatory cells in a loose extracellular matrix.Appearance
During the migratory phase of wound healing
Wound healing refers to a living organism's replacement of destroyed or damaged tissue by newly produced tissue.
In undamaged skin, the epidermis (surface, epithelial layer) and dermis (deeper, connective layer) form a protective barrier aga ...
, 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;
Structure
Granulation tissue is composed of tissue matrix supporting a variety of cell types, most of which can be associated with one of the following functions: * formation ofextracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide ...
;
* operation of the immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from virus
A virus is a submicroscopic infectious agent that replicates only ...
;
* vascularisation;
An excess of granulation tissue (''caro luxurians'') is informally referred to as "proud flesh".Chapter 9 from an "Introduction to Pathology" on a Tuskegee University website
Extracellular matrix
The extracellular matrix of granulation tissue is created and modified by fibroblasts. 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
A scar (or scar tissue) is an area of fibrous tissue that replaces normal skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate
Vertebrates () comprise all animal
Animals are multice ...
tissue.
Immunity
The main immune cells active in the tissue aremacrophages
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer c ...
and neutrophils, although other leukocytes are also present. 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 newextracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide ...
.
In vascularisation, also called angiogenesis
Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature by processes of sprouting and splitt ...
, endothelial cells quickly grow into the tissue from older, intact blood vessels. These branch out in a systematic way, forming anastomoses with other vessels.
References