Chapter_6_part_A_Integumentary_system_mod__2_

Chapter 6: Integumentary System

Overview of Integumentary System

  • Covers body; consists of skin and accessory tissues:

    • Nails

    • Hair

    • Sweat glands

    • Sebaceous glands

  • Integument = skin

  • Cutaneous membrane

  • Acts as a barrier to the outside world

6.1 Composition and Functions of the Integument

Layers of the Integument

  1. Epidermis

  2. Dermis

  3. Subcutaneous layer (hypodermis)

    • Deep to dermis

    • Composed of alveolar and connective tissue

    • Not part of the integumentary system

6.1a Epidermis

General Characteristics

  • Epidermis: Epithelium of the integument

  • Type: Keratinized, stratified squamous epithelium

Layers of the Epidermis (Deep to Superficial)

  1. Stratum Basale

  2. Stratum Spinosum

  3. Stratum Granulosum

  4. Stratum Lucidum (only in thick skin)

  5. Stratum Corneum

  • First three layers contain living keratinocytes

Stratum Details

Stratum Basale

  • Deepest epidermal layer:

    • Single layer of cuboidal to low columnar cells

    • Contains three cell types:

      • Keratinocytes: Large stem cells, divide to regenerate new cells, synthesize keratin

      • Melanocytes: Produce and store melanin, respond to UV light, transfer pigment granules to keratinocytes

      • Tactile cells (Merkel cells): Sensitive to touch, stimulate sensory nerve endings

Stratum Spinosum

  • Composed of several layers of polygonal keratinocytes

  • Nondividing keratinocytes attached by desmosomes

  • Contains epidermal dendritic cells (Langerhans cells) that initiate immune response

Stratum Granulosum

  • Contains 3 to 5 layers of keratinocytes

  • Keratinization begins here:

    • Keratinocytes fill with keratin

    • Nucleus and organelles disintegrate; cells die

Stratum Lucidum

  • Translucent layer with 2 to 3 dead cell layers

  • Present only in thick skin (palms, soles)

  • Cells filled with eleidin

Stratum Corneum

  • Superficial stratum

  • Composed of 20 to 30 layers of dead, interlocking, anucleate keratinized cells

  • Provides protection against abrasion and infection

Skin Color Factors

  • Hemoglobin: Oxygen-binding protein in blood; adds reddish color

  • Melanin: Dark pigment produced in melanocytes; varies by type:

    • Eumelanin: Brown/black shades

    • Pheomelanin: Lighter shades (tan, yellow, red)

    • Albinism: Lack of melanin production

  • Carotene: Yellow-orange pigment from certain vegetables

Skin Markings

  • Nevus (mole): Localized overgrowth of melanocytes

  • Freckles: Localized areas of increased melanocyte activity

  • Hemangiomas: Skin discoloration due to a benign tumor of blood vessels

  • Friction ridges: Fingerprints due to large folds and valleys in the dermis and epidermis

6.1b: Dermis

Overview

  • Deep to epidermis

  • Composed of connective tissue

  • Contains:

    • Blood vessels

    • Sweat glands

    • Sebaceous glands

    • Hair follicles

    • Nail roots

    • Sensory nerve endings

    • Arrector pili

    • Motile dendritic cells

Layers of the Dermis

  1. Papillary layer:

    • Superficial region, areolar connective tissue

    • Dermal papillae interlock with epidermal ridges

  2. Reticular layer:

    • Deeper layer, dense irregular connective tissue

Lines of Cleavage

  • Collagen and elastic fibers oriented in parallel at specific locations

  • Orientation forms lines of cleavage or tension lines:

    • Incisions parallel to these lines heal faster

    • Stretch marks occur when skin is stretched beyond its capability

Other Skin Markings

  • Flexure lines: Dermal folds at joints; cause visible creases

  • Striae (stretch marks): Result from excessive stretching

  • Blisters: Fluid-filled pockets from acute trauma

  • Tattoos: Permanent images created by injecting dye into the dermis

6.1c: Subcutaneous Layer

  • Hypodermis (superficial fascia):

    • Not part of integument

    • Composed of areolar and adipose connective tissue

    • Functions:

      • Protection

      • Energy storage

      • Insulation

    • Common injection site due to extensive vascular network

6.1d Functions of the Integument

  • Produces Vitamin D

  • Regulates body temperature

  • Acts as a barrier to pathogens and physical damage

  • Allows for sensation through receptors

  • Stores lipids in adipose cells