Physiology Topics
There are two types of wound healing processes: surface and deep woud healing.
Since the epidermis has no vasculature, there is no blood loss in a surface wound. The basal layer moves into the wound area from surrounding intact epidermis, by stimuly of epidermal growth factor (EGF). The new basal layer then generates keratinocytes to fill in the gap above.
In a deep wound, blood is released from the dermal vasculature. The first step is the formation of a blood cloth. Factors are released that make nearby blood cells more permeable, allowing immune cells to reach the wound area (inflamatory phase). The clot becomes a scab and basal epithelial cell cells migrate beneath the scab, while fibroblasts migrate beneath the epithelial cells and generate scar tissue (migratory phase). At the same time, blood vessels begin to regrow. Epithelial cells and connective tissue proliferate (proliferative phase). Once the epidermis has been restored, the scab sloughs off and the connective tissue becomes more organized (maturation phase).
Burns are clasified as 1st, 2nd or 3rd degree. First degree burns are minor surface burns involving only the epidermis (includes sunburn). Second degree burns affect the epidermis and part of the dermis. Third degree burns compleately remove both the dermis and epidermis.
There is no spontaneous tissue regeneration after a 3rd degree burn, leading to infection and fluid loss. It is important to cover the area of a 3rd degree burn immediatelly, then try to regenerate the skin. Transplantation of skin from the same patient may be possible in young people with small wounds. In other cases other materials must be used, the most common being cadaver skin, amniotic sac tissue and synthetic collagen "sponge" material. Cadaver skin may be rejected, and there are ethical issues regarding the use of anmiotic sac tissue.
Skin can be artificially synthetized using neonatal skin from circumcitions or an artificial matrix. The problem with skin artificially created by this and other methods is rejecction because it will not vascularize as fas as needed to prevent it from diying out, so it cannot be used in larger areas. Cadaver skin or xenograph (animal skin) transplants usually vascularize faster than artificial skin.
Capillary remanants (endothelial cells) seem to make the difference in the healing of natural skin. Human endothelial cells are hard to grow artificially. They need many growth factors some of them tumorgenic, signaling between fibroblast, keratinocytes and epithelial cells. Breast tissue (from reduction procedures) is used as a matrix to fabricate new skin. Fibroblasts and keratinocites are added, then endothelium from umbilical cords (this tissue is never rejected, but htere are ethical issues). The resulting skin has structures that look like capillaries. The procedure works better if both dermal and epidemal cells are used, suggesting cross comunication between cell types. The components of the signaling mechanism are still unknown and could be the same factors that make blood vessels migrate into new artificial skin or cancer tumor.
Skin is very succeptible to cancer. There are three types of skin cancer: basal cell carcinoma, squamous cell carcinoma and melanoma. Basal cell carcinoma grow relatively slowly, and can be removed, therefore is not as dangerous as other cancers. Squamous cell carcinoma happens to keratinocytes, and is a bit more dangerous that basal cell carcinoma. Melanoma involves melanocites, and is probably due to UV light overexposure. It can spread to limph nodes very fast, and from there to other tissues.
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Need more practice? Answer the review questions below.
1- Describe the process of surface wound healing.
2- Describe the process of deep wound healing.
3- Explain how are burns clasified.
4- How are third degree wouds treated?
5- How is artificial skin synthesized? What are its dissadvantages?
6- What is the importance of endothelial vascular cells in skin regeneration?
7- What is the importance of including either epidermal and/or dermal tissue in skin regeneration?
8- List and brifly describe the types of skin cancers.