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Introduction to Wound Healing

What is Skin?

• A barrier between internal organs and the external environment
• The body’s largest organ contributing to one sixth of the total body weight
• A sensory organ for pain, temperature, and touch
• A protective barrier against disease-causing organisms

 

Structure and Function of the Skin

A. Structure

Epidermis

• The outmost/top layer of the skin
• Has an average thickness of 0.1mm
• Avascular (no blood vessels)
• Divided into five sublayers/strata: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum germinativum (stratum basale)
• Contains four distinct layers of cells:
1. Keratinocytes - Most abundant; Produces keratin which provides mechanical and physical protection as well as producing enzymes and antibiotics that detoxify chemicals that are harmful to the skin
2. Melanocytes - Produce melanin which imparts color to skin and hair
3. Merkel Cells - Play a role in transmission of sensory messages
4. Langerhan Cells – These cells police the outer body surface to take up foreign proteins (antigens) that invade the epidermis; They can travel to a nearby lymphnode where they present the antigens to a type of immune cell called Killer T lymphocyte.
• The external layer is almost completely replaced every three to four weeks

Dermis

• Immediately below the epidermis
• Largest portion of the skin
• Composed of two layers:
1. Papillary
   – Lies directly below the epidermis and contains fibroblasts that form collagen (a component of connective tissue)
2. Reticular
   – Lies beneath the papillary layer and produces collagen and elastin
• Provides tensile strength, mechanical support and protection to the underlying muscles, bones, and organs
• Made up of blood and lymph vessels, nerves, sweat and sebaceous glands and hair roots
• Often referred to as true skin

Hypodermis/Subcutaneous

• Innermost layer of the skin
• Composed of fat, blood vessels, and connective tissue
• Anchors to deep tissue
• Regulates body and skin temperature
• Stores energy in the form of fat

B.  Function

• Facilitates perception of environment – pain, pressure, touch, and temperature
• Provides a barrier against friction, chemicals, heat/cold, pressure, radiation, and microorganisms
• Plays a role in fluid balance, thermal regulation, and facilitates in Vitamin D synthesis

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