Overview
This lecture covers the structure, function, and significance of the skin and the integumentary system, including skin layers, accessory structures, and clinical relevance such as burns and skin cancer.
Integumentary System Overview
- The integumentary system consists of skin and its associated structures.
- Skin is the largest organ and is essential for homeostasis, protection, and sensation.
- It acts as a barrier against damage and pathogens, helps regulate body temperature, and produces vitamin D.
Layers of the Skin
- Skin has three main layers: epidermis (outer), dermis (middle), and hypodermis (inner).
- The epidermis consists mainly of keratinocytes, which produce the tough, water-resistant protein keratin.
- The mnemonic “Can lemurs get some bamboo?” helps remember epidermal layers from outer to inner: Stratum Corneum, Lucidum, Granulosum, Spinosum, Basale.
Epidermal Layers
- Stratum Corneum: Outermost, dead cornified cells; continually shed and replaced.
- Stratum Lucidum: Present only in thick skin (palms, soles); made of transparent, cornified cells.
- Stratum Granulosum: Keratinocytes flatten; contain granules; cells lose organelles here.
- Stratum Spinosum: Multiple keratinocyte layers; contains immune-like cells (macrophage-like); appears spiny under microscope.
- Stratum Basale: Deepest layer; basal cells divide to form new keratinocytes; contains melanocytes (make melanin) and Merkel cells (sense touch).
Dermis
- The dermis contains blood vessels, sweat glands, hair follicles, and nerves.
- Made of connective tissue with collagen (strength) and elastin (elasticity), produced by fibroblasts.
- Has two layers: papillary (looser) and reticular (denser).
- Scarring occurs when the dermis is damaged; scars lack original skin structures and may be less elastic.
Hypodermis
- The hypodermis connects skin to muscle or bone and contains adipose (fat) tissue for insulation.
Accessory Structures
- Sweat glands help cool the body and assist temperature regulation with dermal blood vessels.
- Sebaceous glands produce oil to waterproof and lubricate skin and hair.
- Hair follicles in the dermis produce hair, which is made of keratin.
- Nails grow from the epidermis; nail body is made of dead keratinocytes.
Clinical Relevance: Cancer and Burns
- Skin cancers can arise from different epidermal cells: basal cell carcinoma, melanoma, Merkel cell carcinoma.
- Burns are classified by depth: first degree (epidermis), second degree (epidermis + partial dermis), third degree (full dermis), fourth degree (deeper structures).
- Severe burns compromise fluid balance, protection, and increase infection risk.
Key Terms & Definitions
- Integumentary system — organ system containing skin and its associated structures.
- Keratinocyte — cell that produces keratin protein.
- Keratin — protein providing waterproofing and toughness.
- Cornified cell — dead, flattened cell full of keratin.
- Melanocyte — cell producing melanin (pigment).
- Melanin — pigment protecting against UV rays.
- Merkel cell — cell involved in touch sensation.
- Fibroblast — cell producing collagen and elastin.
- Collagen — protein giving skin strength.
- Elastin — protein providing elasticity.
- Adipose tissue — body fat for insulation.
Action Items / Next Steps
- Review the structure and function of each skin layer and accessory structure.
- Study the classification of burns and types of skin cancer for deeper understanding.