Overview
This lecture covers the structure, function, and importance of skin as the largest organ in the integumentary system, emphasizing its layers, cells, and roles in protection, sensation, and regulation.
The Integumentary System & Skin Functions
- Skin, along with hair, nails, and glands, forms the integumentary system.
- Skin protects the body from infection, injury, extreme temperatures, and fluid imbalance.
- It helps synthesize vitamin D and enables sensory perception.
- Skin regulates body temperature through blood vessels and sweat glands.
- It communicates health and emotions visually (e.g., blushing, sweating).
Skin Anatomy: Three Major Layers
- The three main skin layers are the epidermis (outer), dermis (middle), and hypodermis (subcutis, inner).
- The epidermis is composed of stratified squamous epithelial tissue.
- The dermis contains most skin functions like sensation, blood circulation, and gland activity.
- The hypodermis (subcutis) is mainly adipose tissue, providing insulation, shock absorption, and energy storage.
Epidermis: Structure and Cell Types
- Epidermis is renewed entirely every 4–6 weeks by shedding keratinocytes.
- Keratinocytes produce keratin, giving skin strength, durability, and waterproofing.
- Melanocytes synthesize melanin, determining skin color by melanin quantity, not cell number.
- Langerhans (dendritic) cells act as immune defenders by engulfing pathogens.
- Merkel cells are sensory receptors for touch, found at the epidermis-dermis boundary.
Epidermal Layers (Thick Skin Example)
- Stratum corneum: outermost, dead protective cells.
- Stratum lucidum: clear layer, found only in thick skin (palms/soles).
- Stratum granulosum: keratin-forming, grainy appearance.
- Stratum spinosum: spiny layer, where cells have strong attachments.
- Stratum basale: deepest, regenerative cell layer connecting to dermis.
Dermis and Hypodermis
- Dermis has two layers: papillary (areolar tissue, fingerprint ridges) and reticular (dense connective tissue).
- Contains capillaries, nerve fibers, hair follicles, and glands.
- Hypodermis mainly stores fat and anchors skin to underlying tissue.
Skin Color, Damage, and Care
- Sunlight damages skin (sunburn, cancer risk, immune suppression).
- Tattoos must reach dermis to be permanent.
- Cuts causing bleeding or pain penetrate the dermis.
Key Terms & Definitions
- Keratinocyte — cell producing keratin, the main structural protein in skin.
- Melanocyte — cell creating melanin pigment for skin color.
- Langerhans cell — immune cell in the epidermis, fights invaders.
- Merkel cell — tactile receptor cell for touch sensation.
- Epidermis — outer skin layer, protective and regenerative.
- Dermis — middle skin layer with nerves, blood vessels, and glands.
- Hypodermis (Subcutis) — innermost fatty skin layer for insulation and energy.
- Stratum corneum, lucidum, granulosum, spinosum, basale — five layers of the epidermis in thick skin.
Action Items / Next Steps
- Review layers and cell types of skin.
- Wear sunscreen to protect from UV damage.
- Prepare for next lesson on skin care products and hair/scalp health.