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