Introduction
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SKIN
- The skin is the largest organ (in both surface area & weight!), that covers and protects the external surface of the body.
- Is compised of 3 layers:
- Epidermis
- dermis
- Hypodermis = subcutaneous layer.
* In adults the weight of the skin 4.5-5 Kg. about 16% of total body weight.
Epidermis:
- Is the outermost layer of the skin
▶ Cell types:
The epidermis contains several types of cells:
- Keratinocytes: The most abundant cells in the epidermis, responsible for producing the protein keratin, which provides structural support and waterproofing.
- Melanocytes: Specialized cells that produce the pigment melanin, which helps protect the skin from UV radiation and determines skin color.
- Langerhans cells: Immune cells that patrol the epidermis, helping to identify and fight off pathogens and foreign substances.
- Merkel cells: Touch receptors involved in the sensation of light touch.
▶ Layers: The epidermis is organized into several layers.
- Stratum basale (basal layer): The deepest layer where new keratinocytes are produced through cell division.
- Stratum spinosum (spinous layer): The layer where keratinocytes begin to flatten and develop spiny projections.
- Stratum granulosum (granular layer): The layer where keratinocytes produce keratin and undergo changes in structure.
- Stratum corneum (cornified layer): The outermost layer composed of dead keratinocytes (corneocytes) that are continuously shed from the surface of the skin.
→ In thick skin in fingertips, palms, & soles the is an additional layer:
- Stratum Lucidum (clear layer)
- ↳ consists of 3-5 layers of flatend, clear dead keratinocytes.