Overview
This lecture covers the structure, function, and importance of the integumentary system, focusing on skin layers, accessory structures, and related clinical considerations.
The Integumentary System
- The integumentary system includes skin and associated structures like hair, nails, and glands.
- Skin is the largest organ and is crucial for maintaining homeostasis (body temperature and fluid balance).
- It acts as a physical barrier protecting against injury and pathogens.
- Skin is involved in vitamin D production and sensory perception.
Layers of the Skin
- The skin has multiple layers, each with specific functions and cell types.
- Mnemonic for epidermal layers (outer to inner): "Can Lemurs Get Some Bamboo?" (Corneum, Lucidum, Granulosum, Spinosum, Basale).
Epidermis
- Stratum corneum: outermost layer; dead, cornified cells that are shed.
- Stratum lucidum: present only in thick skin (palms, soles); transparent appearance.
- Stratum granulosum: contains keratinocytes with granules; cells begin to lose organelles.
- Stratum spinosum: several layers of keratinocytes; includes immune cells acting like macrophages.
- Stratum basale: single layer of basal cells doing mitosis; contains melanocytes (produce melanin) and Merkel cells (involved in touch).
Dermis
- Contains blood vessels, sweat glands, hair follicles, and nerves.
- Made of connective tissue with collagen (support) and elastin (elasticity), produced by fibroblasts.
- Has two layers: papillary (loose) and reticular (dense).
- Scars form when dermis is damaged; keloids are raised scars from excessive collagen.
Hypodermis
- Connects skin to underlying muscle and bone.
- Contains adipose (fat) tissue for insulation.
Accessory Structures
- Sweat glands help cool the body; blood vessels in dermis regulate heat loss or retention.
- Sebaceous glands produce oil for waterproofing and lubricating skin and hair.
- Hair follicles are in the dermis; hair is made of keratinized, non-living cells.
- Nails grow from the epidermis and are made of dead keratinocytes.
Clinical Considerations
- Skin cancers arise from abnormal cell division in basal cells, melanocytes, or Merkel cells.
- Burn classification: first degree (epidermis), second degree (epidermis + part dermis), third degree (epidermis + all dermis), fourth degree (extends to bone/muscle).
- Severe burns compromise protection, fluid balance, and increase infection risk.
Key Terms & Definitions
- Integumentary system — organ system including skin, hair, nails, and glands.
- Keratinocytes — epidermal cells producing keratin protein.
- Keratin — protein providing strength and water resistance.
- Melanocyte — cell in the basal layer producing melanin pigment.
- Melanin — pigment protecting against UV radiation.
- Papillary layer — upper dermis with loose connective tissue.
- Reticular layer — deeper dermis with dense connective tissue.
- Fibroblast — cell making collagen and elastin in the dermis.
- Adipose tissue — fat tissue in the hypodermis for insulation.
Action Items / Next Steps
- Review skin layer mnemonics and structures.
- Study burn classifications and skin cancer types.
- Consult further reading for details on Merkel cells and burn degree classification.