Week 5: Layers of the skin

Page 1: Introduction to Layers of the Skin

• Overview of topics:

  • Types and functions of cells in skin layers

  • Functions of skin layers

  • Mechanism of body temperature regulation

  • Accessory structures of the integumentary system

• Key Cell Types:

  • Keratinocytes: make up 90% of epidermal cells, provide waterproof texture by producing keratin.

  • Langerhans cells: act as resident macrophages, initiate immune responses against microbes.

• Dermis Composition:

  • Contains collagen and elastic fibers that maintain tensile strength.

  • Prevents dermis from stretching or pulling.

Page 2: Cells and Functions of the Epidermis

• Epidermis Structure:

  • Consists of four principal cell types:

    • Keratinocytes:

      • Predominant cell type (90%)

      • Produces keratin for protection and waterproofing.

    • Melanocytes:

      • Produce melanin, which gives color and protects against UV radiation.

      • Function by linking to keratinocytes and transporting melanin granules.

    • Langerhans Cells:

      • Immune response cells, migrate from bone marrow.

      • Damage easily by UV light.

    • Merkel Cells:

      • Receptors connected to dermal nerve fibers, function as touch sensors.

Page 3: Functions and Cells of the Dermis

• Dermis Composition:

  • Comprised of connective tissue with various cell types:

    • Fibroblasts: synthesize fibers and extracellular matrix.

    • Histiocytes: tissue macrophages aiding the immune system.

    • Mast Cells: inflammatory cells, crucial for immune responses.

    • Adipocytes: fat storage, insulation, and aiding hair regeneration.

• Structure:

  • Divided into papillary and reticular layers:

    • Papillary Layer: supplies nutrients to epidermis.

    • Reticular Layer: provides strength and elasticity through collagen and elastic fibers.

Page 4: Collagen, Fibroblast, and Elastin

• Reticular Layer Function:

  • Contains hair follicles and various glands.

• Fiber Functions:

  • Collagen: Provides tensile strength.

  • Elastic Fibers: Can stretch to 140% of original length.

  • Reticular Fibers: Thinner type of collagen forming a support network.

Page 5: Thermoregulation

• Mechanisms of thermoregulation:

  • Sweat Evaporation: cooling via sweat glands.

  • Insulation: Adipose tissue in hypodermis provides insulation.

  • Vasodilation/Vasoconstriction: Adjusts blood flow to manage heat loss or retention.

Page 6: Mechanoreceptors of the Skin

• Mechanoreceptors Overview:

  • Respond to touch, pressure, stretching, sound waves, motion.

• Types of Tactile Mechanoreceptors:

  • Merkel's Disks: Touch receptors attached to sensory neurons.

  • Ruffini Corpuscles: Sense skin stretching and movement.

  • Meissner Corpuscles: Enhance sensitivity to light touch, located in hairless skin.

  • Pacinian Corpuscles: Detect deep pressure and vibration in the dermis.

Page 7: Structure and Function of Hair

• Hair Growth Overview:

  • Hair structure: keratinized cells, grows from hair follicles.

  • Hair parts: hair shaft (above skin) and root (below skin).

Page 8: Layers of Hair

• Structure of Hair:

  • Contains three layers:

    • Medulla: loosely arranged cells.

    • Cortex: bulk of hair, tightly packed keratinized cells.

    • Cuticle: thin, scaly cells overlapping like shingles.

Page 9: Associated Structures of Hair

• Composition around Hair Follicle:

  • Contains nerves and arrector pili muscles for movement.

  • Hair functions include:

    • Insulation and protection from UV rays.

    • Sensory detection for movements on the skin.

Page 10: Hair Growth Cycle

• Phases of Hair Follicle Development:

  • Anagen (Growing Phase): lasts 6-8 years, hair grows about 1mm every 3 days.

  • Catagen (Retraction Phase): lasts 2-3 weeks, the follicle shrinks and hair becomes "club hair".

  • Telogen (Resting Phase): lasts 1-3 months, hair rests and can be easily pulled out.

Page 11: Structure and Function of the Nail

• Nail Composition and Features:

  • Composed of dead cells filled with hard keratin.

  • Includes:

    • Free Edge: overhangs at the tip.

    • Nail Body: attached to finger.

    • Nail Root: extends under skin.

Page 12: Additional Nail Anatomy

• Important Features:

  • Lunule: thickening of the matrix at the proximal nail end.

  • Eponychium (Cuticle): narrow zone of dead skin.

  • Nails provide diagnostic information based on appearance.

Page 13: Structure of Integumentary System

• Exocrine Glands Types:

  • Eccrine Sweat Glands: sweat for cooling, widespread in body.

  • Apocrine Sweat Glands: produce thick sweat, found in specific body areas.

  • Sebaceous Glands: produce oily sebum to keep skin moist.

  • Ceruminous Glands: produce cerumen (earwax) in ear canal.

  • Mammary Glands: modified apocrine glands for milk production in lactation.

Page 14: Functions of Integumentary Glands

• Overview of Gland Functions:

  • Eccrine Glands: distribute sweat to cool skin and eliminate toxins.

  • Tactile cells and Langerhans cells role in immune protection and sensation.

  • Hypodermis: primarily composed of adipose for insulation and energy storage.

Page 15: Merocrine and Apocrine Glands

• Distinction between Gland Types:

  • Merocrine Sweat Glands: widely distributed, cool skin, eliminate waste.

    • Releases insensible perspiration through surface contact.

  • Apocrine Sweat Glands: located in restricted areas, involved in scent production.