Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. In Physiology, perfusion is the process of nutritive delivery of Arterial Blood to a Capillary bed in the Biological tissue. Fibrin (also called Factor Ia) is a Protein involved in the clotting of blood Wound healing, or wound repair, is the body's natural process of regenerating dermal and epidermal tissue. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals.

Appearance

Example of Granulation tissue from a cut on a finger with "proud flesh".

During the proliferative phase of wound healing, granulation tissue is:

• light red or dark pink in color, being perfused (permeated) with new capillary loops or "buds";
• soft to the touch;
• moist; and
• bumpy (granular) in appearance. Wound healing, or wound repair, is the body's natural process of regenerating dermal and epidermal tissue.

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:

• extracellular matrix,
• immune system, or
• vascularisation. In Biology, the extracellular matrix ( ECM) is the Extracellular part of animal tissue that usually provides structural support to the cells An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Angiogenesis is a physiological process involving the growth of new Blood vessels from pre-existing vessels

An excess of granulation tissue is informally referred to as "proud flesh. "^[1]

Extracellular matrix

The extracellular matrix of granulation tissue is created and modified by fibroblasts. A fibroblast is a type of cell that synthesizes and maintains the Extracellular matrix of many Animal tissues Initially, it consists of a network of Type III collagen, a weaker form of the structural protein that can be produced rapidly. Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein This is later replaced by the stronger, long-stranded Type I collagen, as evidenced in scar tissue. Scars (also called cicatrices) are areas of fibrous tissue that replace normal Skin (or other tissue after injury

Immunity

The main immune cells active in the tissue are macrophages and neutrophils, although other leukocytes are also present. Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of White blood cells in humans and form an essential part of the These work to phagocytize old or damaged tissue, and protect the healing tissue from pathogenic insult. 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 defence.

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. A fibroblast is a type of cell that synthesizes and maintains the Extracellular matrix of many Animal tissues In Biology, the extracellular matrix ( ECM) is the Extracellular part of animal tissue that usually provides structural support to the cells

In vascularisation, also called angiogenesis, endothelial cells quickly grow into the tissue from older, intact blood vessels. Angiogenesis is a physiological process involving the growth of new Blood vessels from pre-existing vessels The endothelium is the thin layer of cells that line the interior surface of Blood vessels forming an interface between circulating Blood in the The blood vessels are part of the Circulatory system and function to transport Blood throughout the body These branch out in a systematic way, forming anastomoses with other vessels. An anastomosis (plural anastomoses, from gr ἀναστόμωσις communicating opening) is a Network of streams that both branch out and reconnect

References

1. ^ Healing and Repair Chapter 9 from an "Introduction to Pathology" on a Tuskegee University website