What is the Difference Between Epithelialization and Granulation

The main difference between epithelialization and granulation is that epithelialization is the process of epidermis regeneration over a partial-thickness wound surface or the scar tissue formation on the full thickness of the wound, whereas granulation is the formation of new connective tissue and blood vessels in pink or red color.

Epithelialization and granulation are two types of processes occurring in a wound

Key Areas Covered

1. What is Epithelialization
     – Definition, Structure, Function
2. What is Granulation
     – Definition, Structure, Function
3. Similarities Between Epithelialization and Granulation
     – Outline of Common Features
4. Difference Between Epithelialization and Granulation
     – Comparison of Key Differences

Key Terms

Epithelialization, Granulation

What is Epithelialization

Epithelialization is the process of regenerating the epidermis over a partial-thickness wound surface or the formation of scar tissues on a full-thickness wound. The epithelial tissue has a light pink color with a shiny pearl appearance. During epithelialization, epithelial tissues travel from the outward wound edges, crawling across the wound bed to close the wound. Keratinocytes are the main cellular component of the epithelial cells, and they are responsible for restoring the epidermis after injury. Keratinocytes occur in the several layers of the stratified epithelium of the skin. They provide a physical barrier between the environment and the organism.

Figure 1: Epithelialization

During wound healing, keratinocytes from the basal layer undergo proliferation. The infrastructure of the keratinocytes is composed of keratin filaments known as K5 and K14. Keratinocytes transfer towards the traversing layers, such as the spinous layer, granular layer, and stratum corneum. Keratinocytes undergo differentiation during this transfer. They synthesize K5 and K14 in the basal layer and K1 and K10 in the suprabasal layer. Hemidesmosomes and the focal adhesions of the basal layer as well as the desmosomes of the suprabasal layer are disconnected to migrate keratinocytes during epithelialization.  

What is Granulation

Granulation is the formation of new connective tissue and microscopic blood vessels on the surface of the wound during wound healing. Granulation starts from the base of the wound, and it can take up any size of the wound. Histological appearance of granulation occurs as the proliferation of fibroblasts and angiogenesis, the formation of thin, delicate capillaries. During wound healing, the forming granulation tissue appears pink or red in color, perfused with new capillary loops called buds. It is moist and soft to the touch. It may have a bumpy appearance due to punctate hemorrhages. In addition, it is painless when healthy.

Figure 2: Granulation

Moreover, a variety of cell types is involved in the formation of granulation tissue during wound healing. Their functions include the formation of an extracellular matrix, immune system operations, and vascularization.

Similarities Between Epithelialization and Granulation

• Epithelialization and granulation are two processes occurring during the processes of wound healing.
• Both processes form new tissue.

Difference Between Epithelialization and Granulation

Definition

Epithelialization refers to a process of covering the denuded epithelial surface, while granulation refers to the development of new tissue and blood vessels in a wound during the healing process.

Type of Tissue

Epithelialization generates new epithelial tissue, while granulation tissue is connective tissue with blood vessels.

Occurrence

Moreover, epithelialization occurs from the wound edges, while granulation occurs from the middle of the wound.

Appearance

Epithelialization occurs in light pink color with a shiny pearl appearance, while granulation occurs in red or pink color.

Conclusion

In brief, epithelialization and granulation are two processes occurring during wound healing. Each process forms different types of tissues in the wound. Epithelialization is the process of covering the epithelial surfaces of the wound. It starts from the edges of the wound. It also forms epithelial cells from the edge of the wound. The appearance of the forming epithelial tissue is either light pink or shiny pearl color. In comparison, granulation is the formation of the connective tissue and blood vessels from the middle of the wound. Healthy connective tissue occurs in red to pink color. Therefore, the main difference between epithelialization and granulation is the type of tissue formed in each process.

References:                     

1. Pastar I, Stojadinovic O, Yin NC, Ramirez H, Nusbaum AG, Sawaya A, Patel SB, Khalid L, Isseroff RR, Tomic-Canic M. Epithelialization in Wound Healing: A Comprehensive Review. Adv Wound Care (New Rochelle). 2014 Jul 1;3(7):445-464. doi: 10.1089/wound.2013.0473. PMID: 25032064; PMCID: PMC4086220.
2. “Granulation tissue.” Wikipedia. Wikimedia Foundation.

Image Courtesy:

1. “Epithelial Tissues Simple Cuboidal Epithelium (41681552432)” By Berkshire Community College Bioscience Image Library – Own work (CC0) via Commons Wikimedia
2. “Finger with granulation tissue” By Stiepan Pietrov – Own Work (Public Domain) via Commons Wikimedia