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Granulation tissue is new connective tissue 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.
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
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 again ...
, 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
Palpation is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness. Usually performed by a health care practitioner, it is the process of feeling an object in or on the body to determine ...
;
* 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 s ...
;
* operation of the immune system;
* vascularisation
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 circulatory system, vasculature by processes of spr ...
;
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
A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells ...
. 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
Type I collagen is the most abundant collagen of the human body. It forms large, eosinophilic fibers known as collagen fibers.
It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endomys ...
, as evidenced in scar
A scar (or scar tissue) is an area of fibrous tissue that replaces normal skin after an injury. Scars result from the biological process of wound repair in the skin, as well as in other organs, and tissues of the body. Thus, scarring is a n ...
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 ce ...
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 s ...
.
In vascularisation, also called angiogenesis, endothelial cells
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...
quickly grow into the tissue from older, intact blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s. These branch out in a systematic way, forming anastomoses
An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be norm ...
with other vessels.
References