Overview
This lecture covers the integumentary system with a focus on the epidermis, detailing its structure, cell types, and the differences between thick and thin skin.
Introduction to the Integumentary System
- The integumentary system consists of the skin and its derivatives: nails, hair, sweat glands, and sebaceous (oil) glands.
- The skin (cutaneous membrane) acts as a barrier separating the body from the external environment.
- Dermatology is the study and treatment of the integumentary system.
Structure of the Skin
- The skin is composed of two main layers: the epidermis (outer) and dermis (inner); the subcutaneous (hypodermis) layer is not part of the skin.
- The dermis is divided into the papillary (top) and reticular (bottom) layers.
- Structures in the skin include hair follicles, sensory receptors, arrector pili muscles, oil glands, sweat glands, arteries, and veins (outside the epidermis).
Layers of the Epidermis
- The epidermis has five layers (from deep to superficial): stratum basale, spinosum, granulosum, lucidum, and corneum.
- The mnemonic "Big Stinky Gorillas Like Corn" aids in remembering the order.
- The first three layers contain living keratinocytes, while the last two have dead keratinized cells.
Epidermal Cell Types
- Keratinocytes: Most abundant, produce keratin for strength, originate from stem cells in the stratum basale.
- Melanocytes: Produce melanin pigment, protect DNA from UV radiation, and transfer melanin to keratinocytes.
- Tactile (Merkel) Cells: Few in number, detect touch, release chemicals to stimulate sensory nerves.
- Dendritic (Langerhans) Cells: Immune cells in the spinosum, detect pathogens and cancerous cells.
Characteristics of Epidermal Layers
- Stratum Basale: Deepest, single cell layer, contains stem cells, keratinocytes, melanocytes, and tactile cells.
- Stratum Spinosum: Several layers, contains specialized keratinocytes connected by desmosomes, and dendritic cells.
- Stratum Granulosum: 3-5 layers, cells fill with keratin and die, first layer of dead keratinized cells.
- Stratum Lucidum: 2-3 translucent layers, only in thick skin (palms, soles), contains eleidin protein.
- Stratum Corneum: 20-30 layers of dead, interlocking keratinized cells, forms a tough barrier, creates an acidic surface (acid mantle).
Migration and Renewal of Epidermal Cells
- Keratinocytes originate in the stratum basale, move upward, become keratinized, lose their nucleus, and are shed after about 4 weeks.
Thick vs. Thin Skin
- Thick skin: Contains all five epidermal layers, found on palms, soles, fingers, toes, has sweat glands, no hair or sebaceous glands, thickness 0.4–0.6 mm.
- Thin skin: Lacks the stratum lucidum, covers most of the body, contains hair, sweat, and oil glands, thickness 0.075–0.15 mm.
Key Terms & Definitions
- Integumentary System — skin and its accessory structures.
- Epidermis — outer layer of the skin, avascular, with multiple strata.
- Keratinocyte — main cell type that produces keratin protein.
- Melanocyte — cell that produces melanin pigment for UV protection.
- Tactile (Merkel) Cell — sensory cell for touch detection.
- Dendritic (Langerhans) Cell — immune cell within the epidermis.
- Stratum Basale/Spinosum/Granulosum/Lucidum/Corneum — sequential layers of the epidermis.
Action Items / Next Steps
- Review diagrams and images of skin layers for visual understanding.
- Memorize the order and main features of the epidermal layers.
- Prepare for upcoming lectures on the dermis and hypodermis.