Overview
This lecture covers the structure and layers of the skin (integument), distinguishing features of thin and thick skin, and the functions of associated accessory structures.
Skin Layers Overview
- The integument is divided into two main layers: epidermis (outer) and dermis (inner).
- Thick skin has an extra cell layer and a thicker outermost layer than thin skin.
Layers of the Epidermis (Superficial to Deep)
- Stratum corneum: outer, hard, keratinized layer.
- Stratum lucidum: clear single layer present only in thick skin.
- Stratum granulosum: layer of elliptical cells, site of granular formation.
- Stratum spinosum: spiny layer where keratin production begins.
- Stratum basale (germinativum): deepest, contains dividing stem cells, sits on the basement membrane.
Special Features of the Epidermis
- Basement membrane separates the epidermis from the dermis.
- Epidermal ridges (waviness) follow dermal papilla, help form fingerprints.
Layers of the Dermis
- Papillary layer: upper dermis, contains capillaries within dermal papillae.
- Reticular layer: deep dermis, dense irregular connective tissue, houses accessory structures like hair follicles and glands.
Accessory Structures in the Dermis
- Hair follicles originate in the reticular layer and include sebaceous (oil) glands.
- Arrector pili muscle (smooth muscle) makes hair stand on end for insulation and threat display.
- Sweat glands: merocrine (watery, all over body) and apocrine (in groin/armpits, not shown).
- Sensory structures: tactile (Meissner's) corpuscles for touch in papillae, lamellated corpuscles for deep pressure/vibration.
Hypodermis (Subcutaneous Layer)
- Hypodermis is mainly adipose and areolar connective tissue, not part of the integument.
- Provides insulation, energy storage, and allows skin to move independently over muscles.
- Thickness varies with climate adaptation and physical activity (e.g., cold climates, swimmers).
Key Terms & Definitions
- Epidermis — outermost skin layer; stratified squamous epithelium.
- Dermis — underlying connective tissue layer; supports epidermis.
- Stratum corneum — hardened, keratin-filled outer layer of the epidermis.
- Stratum lucidum — clear layer present only in thick skin.
- Stratum granulosum — granular cell layer in the epidermis.
- Stratum spinosum — spiny cell layer where keratin begins.
- Stratum basale (germinativum) — deepest epidermal layer with stem cells.
- Dermal papillae — projections into epidermis, forming ridges.
- Papillary layer — upper dermis, contains capillary loops.
- Reticular layer — deep dermis, dense tissue with accessory structures.
- Arrector pili muscle — smooth muscle raising hair for insulation or display.
- Hypodermis (subcutaneous) — tissue beneath dermis, mainly fat and loose connective tissue.
Action Items / Next Steps
- Review the structure and functions of each skin layer.
- Study key accessory structures and their locations/functions within the skin.
- Prepare to identify skin layers and accessory structures on diagrams or models.