Chapter 5 - integumentary system

Integumentary System Lecture Notes
Section 1: Functional Anatomy of the Skin

Overview of the Integumentary System

  • Components: Skin (cutaneous membrane) and various accessory structures.

  • Significance:

    • Most accessible organ system.

    • Represents 16% of total body weight and has a surface area of 1.5–2 m².

    • Acts as the body’s first line of defense against the environment.

Major Components

  • Cutaneous Membrane:

    • Epidermis: Stratified squamous epithelium.

    • Dermis: Composed of the papillary layer (areolar connective tissue) and reticular layer (dense irregular connective tissue).

  • Accessory Structures:

    • Hairs: Provide protection and sensory functions.

    • Nails: Protect tips of fingers and toes.

    • Exocrine glands:

    • Sebaceous glands: Produce sebum to lubricate skin.

    • Sweat glands: Help in thermoregulation and waste excretion.

    • Sensory receptors and nerve fibers: Detect stimuli, providing feedback to the nervous system.

    • Arrector pili muscles: Small muscles that cause hair to stand on end.

    • Cutaneous plexus: Network of blood vessels.

Functions of the Integumentary System

  1. Protects underlying tissues and organs from various types of damage (impact, abrasion, fluid loss, chemical attack).

  2. Excretion of salts, water, and organic wastes through integumentary glands.

  3. Thermoregulation: Maintains normal body temperature via insulation or evaporative cooling.

  4. Synthesis of melanin: Protects underlying tissue from ultraviolet (UV) radiation.

  5. Synthesis of keratin: Aids in protection against abrasion and provides water repellency.

  6. Vitamin D3 production: Converts to calcitriol, essential for normal calcium metabolism.

  7. Storage of lipids: Stored in adipocytes within the dermis and subcutaneous layer.

  8. Detection of stimuli: Enables the sensation of touch, pressure, pain, and temperature, relayed to the nervous system.

Section 2: The Epidermis

Structure of the Epidermis

  • Composition: Multiple layers of cells (strata), primarily keratinocytes.

  • All epidermal layers are avascular.

  • Movement of cells: From deepest stratum to most superficial layer takes about 7–10 days.

  • Epidermal layers:

    • Stratum basale: Stem cells for keratinocyte renewal; contains Merkel cells.

    • Stratum spinosum: Provides strength and flexibility; contains Langerhans cells (immune response).

    • Stratum granulosum: Keratin and keratohyalin production starts; cells become thinner and flatter.

    • Stratum lucidum: Found only in thick skin; consists of dead keratin-filled cells.

    • Stratum corneum: Outermost layer with 15-30 layers of dead, keratinized cells; water-resistant.

Types of Skin

  • Thin skin: Covers most of the body, containing only four strata.

  • Thick skin: Found on palms and soles, containing five strata.

  • Fingerprints: Unique patterns from epidermal ridges, essential for identification, unchanging throughout life.

Skin Color Factors

  • Pigments:

    • Carotene: Orange-yellow pigment.

    • Melanin: Brown, yellow-brown, or black pigment produced by melanocytes in the stratum basale. Differences in skin pigmentation are due to the amount of melanin produced, not the number of melanocytes.

  • Dermal circulation: Influenced by blood flow; oxgenation changes coloration (e.g., cyanosis is a blue coloration due to inadequate blood flow).

Skin Cancer

  • Basal Cell Carcinoma: Most common skin cancer; originates in the stratum basale due to UV radiation exposure, generally has a high survival rate.

  • Malignant Melanoma: A dangerous form of skin cancer that can metastasize; high survival rate if detected early but drastically drops if metastasized.

Section 3: The Dermis and Subcutaneous Layer

Dermis Structure

  • Divided into two layers:

    • Papillary layer: Contains areolar tissue with capillaries and sensory neurons.

    • Reticular layer: Dense, irregular connective tissue containing glands and larger blood vessels.

Subcutaneous Layer (Hypodermis)

  • Sits beneath the dermis; consists of adipose tissue that stores energy and insulates.

Functions of the Dermis and Subcutaneous Layer

  • Provides strength and elasticity to the skin.

  • Houses nerves, blood vessels, and glands essential for functions of the skin.

Section 4: Clinical Module - Burns

Classification of Burns

  • First-degree burn: Affects only the surface of the epidermis; characterized by redness (erythema).

  • Second-degree burn: Damages entire epidermis and part of the dermis; includes blistering and pain.

  • Third-degree burn: Involves full-thickness damage to epidermis and dermis; might necessitate skin grafts.

Assessment of Burns

  • Rule of Nines: Estimation of body surface area affected by burns:

    • Head: 9%

    • Upper limb: 9% each

    • Trunk: 36% (front and back)

    • Genitalia: 1%

    • Lower limb: 18% each

Skin Grafts

  • Types:

    • Split-thickness graft: Transfers epidermis and superficial dermis.

    • Full-thickness graft: Transfers epidermis and both layers of dermis.

    • Sources of graft material:

    • Autograft: Skin from the patient’s own body.

    • Allograft: Skin from a cadaver.

    • Xenograft: Skin from an animal.

Section 5: Accessory Structures of the Skin

Overview of Accessory Structures

  • Components:

    • Hair follicles, exocrine glands, and nails.

    • Originate from the epidermis during embryological development.

Hair Structure and Function

  • Two types of hair: Terminal (thicker, darkly pigmented) and vellus (fine, lighter hair).

  • Hair Growth: Involves an active phase (growth) and a resting phase (shedding).

Exocrine Glands Functions

  • Sebaceous Glands: Produce sebum for nourishment and antimicrobial action.

  • Sweat Glands Types:

    • Apocrine: Secretes odoriferous substance found in specific areas.

    • Eccrine: Primarily involved in thermoregulation.

Section 6: Clinical Module - Age-Related Changes in the Integument

Changes with Aging

  • Fewer melanocytes: Leads to paler skin and increased UV sensitivity.

  • Drier epidermis: Associated with decreased sebaceous gland activity, leading to skin becoming more prone to injury.

  • Thinning of epidermis: Diminished connectivity between epidermis and dermis, increasing injury risks.

  • Reduced immune response: Decreased presence of dendritic cells, increasing skin damage risk.

  • Diminished blood supply: Causes temperature regulation issues.

Section 7: Endocrine Interactions

Hormonal Effects on Skin

  • Hormones facilitate communication and maintain skin health and repair.

  • Vitamin D3 Production: Processes influenced by sunlight exposure crucial for bone health.

Integumentary Repair Mechanisms

  • Phases of Skin Regeneration:

    1. Inflammation Phase: Initiates repair by vascular response.

    2. Migration Phase: Blood clot formation and cellular migration for repair.

    3. Proliferation Phase: Tissue reconstruction.

    4. Scarring Phase: Formation of scar tissue after repair completion.