Integumentary System Lecture Notes

Introduction

• Part 1 of Chapter 5 on the Integumentary System
• Analogy of skin to a high-tech jacket with features: waterproof, stretchable, washable, self-repairing, lifetime guarantee
• Integumentary System: Refers to the skin, the body's largest organ

Skin as an Organ

• Skin is an organ composed of multiple tissue types: epithelial, connective, muscle, and nervous tissue
• Accounts for 7% of total body weight
• Varies in thickness (1.5 mm to 4 mm)
• Thickness varies by location: thinner on forearms, thicker on palms and soles

Functions of the Skin

• Protection: Acts as a barrier against environmental damage
• UV Protection: Melanocytes produce melanin to protect against UV rays
• Vitamin D Production: Stimulated by UV light, crucial for calcium absorption
• Thermal Regulation: Vasodilation and vasoconstriction manage heat retention and release
• Waterproofing: Prevents water loss
• Sensation: Contains receptors for pressure, temperature, and pain
• Waste Excretion: Through sweat glands, excretes urea and salts

Structure of the Skin

Layers of the Skin

• Epidermis: Outermost layer, composed of stratified squamous epithelium
  • Stratum Basale: Single cell layer; contains keratinocytes, melanocytes, and Merkel cells
  • Stratum Spinosum: Several layers thick; contains keratinocytes and Langerhans cells
  • Stratum Granulosum: 1-5 layers; contains keratohyaline and lamellated granules
  • Stratum Lucidum: Only in thick skin; clear layer
  • Stratum Corneum: Thickest layer; dead keratinized cells
• Dermis: Below the epidermis; composed of connective tissue
  • Papillary Layer: Superficial 20%; contains dermal papillae
  • Reticular Layer: Deeper 80%; contains dense irregular connective tissue
• Hypodermis: Not part of the skin; contains fat, anchors skin to underlying structures

Cells of the Epidermis

• Keratinocytes: Produce keratin, most abundant
• Melanocytes: Produce melanin, protect against UV
• Merkel Cells: Touch receptors
• Langerhans Cells: Immune response, acts as macrophages

Skin Pigmentation

• Melanin: Brown-black pigment; amount and type varies with genetics and UV exposure
• Carotene: Yellow-orange pigment from diet
• Hemoglobin: Red pigment from blood; visible in lighter skin

Additional Skin Functions

• Friction Ridges (Fingerprints): Enhance grip, caused by dermal ridges
• Thermoregulation: Controlled by blood flow in dermal vessels
• Elasticity: Collagen and elastic fibers provide strength and flexibility
• Striae (Stretch Marks): Caused by tearing of collagen fibers in the dermis

Importance of Skin Care and Maintenance

• Regular exfoliation due to skin shedding (~40 pounds in a lifetime)
• Importance of cleaning living spaces and personal items to remove dead skin and oils

Conclusion

• Understanding the structure and function of the skin is crucial for comprehending overall body protection and health.

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This concludes Part 1 of the lecture on the Integumentary System. Part 2 will continue in the next session.