Overview
This lecture explains the five layers of the epidermis, their main characteristics, and the cell types found in each, defining key terms and functions for each layer.
Structure of the Skin
- The skin has three main parts: epidermis (outer), dermis (middle), and subcutaneous tissue/hypodermis (inner).
- The epidermis is composed of five distinct layers, or strata, each with specific functions.
Layers of the Epidermis
- Stratum basale: Deepest layer where new keratinocytes are produced and rapid cell division occurs.
- Melanocytes found here produce melanin pigment, which determines skin color.
- All people have a similar number of melanocytes; skin color depends on melanin amount.
- Stratum spinosum: Located above the basale, named for spiny appearance due to desmosomes (cell connections).
- Contains Langerhans cells, which are immune cells protecting against pathogens.
- Stratum granulosum: Characterized by keratohyalin granules, which contain proteins that help manage keratin.
- Releases lamellar bodies that form a lipid layer, making the skin waterproof.
- Stratum lucidum: Consists of dead, clear keratinocytes that have lost nuclei and organelles, making the layer transparent.
- Stratum corneum: Outermost layer of dead, flat keratinocytes (15–20 layers thick) that continuously slough off; reptiles shed this whole layer when molting.
Key Terms & Definitions
- Epidermis — The outermost layer of the skin, composed of five layers of cells.
- Keratinocyte — A cell that produces keratin, the main structural protein of the epidermis.
- Cytokeratin/Keratin — Intermediate filament protein that gives skin strength and toughness.
- Melanocyte — Cell in the stratum basale that produces melanin pigment.
- Melanin — Pigment determining skin color; more melanin means darker skin.
- Desmosome — Structure connecting keratinocytes in the stratum spinosum, giving a spiny appearance.
- Langerhans cell — Immune cell in the epidermis that protects against pathogens.
- Keratohyalin granule — Granules containing proteins that process and transport keratin.
- Lamellar body — Secretory structure releasing lipids to waterproof the skin.
Action Items / Next Steps
- Review the five strata of the epidermis and their unique functions.
- Prepare for a discussion of the dermis and hypodermis in the next lesson.