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Healing Process

Components

(Section 2c. Components of Wound Healing continued)

Extra-cellular Matrix

The extra-cellular matrix is composed of structured proteins mainly collagen, functional protein such as fibronectin and growth factors, ground substance made mainly of glycosaminoglycans and hyaluronic acid. Each component has very specific properties in the wound healing process.

Matrix Proteins

Collagen - This protein is the major building block of connective tissue. The mature collagen fiber found in dermis is composed of collagen units formed into a complex and very strong filament. The fibers are formed outside the fibroblast, oriented by matrix signals and through proteoglycan contact. Of the many types of collagen, type I is the most abundant in normal skin. Type III collagen provides cell guidance plus this protein can distend providing flexibility to dermis and elements such as blood vessel walls. Besides dermal structure, collagen type I provides a contact orientation for dividing and migrating epithelial cells.

Collagen Types & Actions
Molecule	Source	Location/Action
Collagen Type I	Fibroblasts	Dermis Increase epidermal cell attachment and spreading contact orientation for dividing and migrating epithelial cells.
Collagen Type III	Fibroblasts	Found in dermis and around blood vessels providing flexibility. Increased amounts seen in the initial phase of healing provides scaffolding to dermis
Collagen Type IV	Epidermal cells Fibroblasts	Lamina densa Contact orientation for dividing cells Supports epidermal cell attachment and spreading
Collagen Type V	Fibroblasts	Properties similar to type II

Fibronectin - This adhesion protein, produced mainly by fibroblasts and macrophages, is a large glycoproteins found in all tissues and plasma. One of its key functions is an an attachment protein for skin cells via collagen type I. Production is induced with any acute wound. Fibronectin plays a major role in wound healing and has been shown to increase the healing rate of chronic wounds when applied topically.

Fibronectin Functions:

Adherence Function

Crosslinking to fibrin (and collagen) causing adherence of tissues to each other
Key adherence molecule attaching epithelial and endothelial cells at cell junctions
Contact orientation for all cells in the healing process

Epithelialization

Cell migration, spreading, and orientation
Cell division
Cell re-adherence to form a layer

Chemo Attractants (Fibronectin Fragments)

for fibroblasts
for macrophages

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