Ch. 5 The Integumentary System(2)

Chapter 5 - The Integumentary System

Structure of Skin

  • Skin (Integument): Composed of three major regions:

    • Epidermis: Superficial region

    • Dermis: Middle region

    • Hypodermis: Deepest region; contains mostly adipose tissue and is not technically part of the skin.

Components of Skin

  • Hair shaft, Epidermis, Dermis, and other structures:

    • Nervous Structures: Include sensory nerve fibers and receptors such as lamellar corpuscles and hair follicle receptors.

    • Appendages:

      • Eccrine sweat glands

      • Arrector pili muscles

      • Sebaceous (oil) glands

Epidermis Characteristics

  • Outer portion exposed to the environment;

  • Composition:

    • Keratinized stratified squamous epithelium with four or five layers (varies by body region);

    • Avascular: No blood vessels present.

    • Key Cell Types:

      • Keratinocytes: Produce keratin for protection.

      • Melanocytes: Synthesize melanin, pigment responsible for skin color.

      • Merkel Cells: Sensitive to light touch function alongside sensory nerve endings.

      • Langerhans' Cells: Immune cells that activate immune responses.

Layers of the Epidermis

  • Stratum Corneum:

    • Composed of 20–30 rows of dead keratinized cells;

    • Functions as a protective barrier against environmental damage.

  • Stratum Lucidum:

    • Present only in thick skin (e.g., palms, soles);

    • Consists of several rows of flat, dead keratinocytes.

  • Stratum Granulosum:

    • Keratinization begins;

    • Contains lamellated granules for water loss prevention;

    • Cells begin to die above this layer.

  • Stratum Spinosum:

    • Several layers thick, characterized by pre-keratin filaments;

    • Contains abundant melanin granules and Langerhans' cells.

  • Stratum Basale:

    • Deepest layer with actively dividing stem cells, including melanocytes;

    • The journey from this layer to the surface takes about 25–45 days.

Dermis

  • Second major region of skin containing flexible connective tissue:

    • Composed of fibroblasts, macrophages, and occasionally mast and white blood cells.

    • Two Layers:

      • Papillary Layer: Contains areolar connective tissue, dermal papillae (for nutrient supply), and sensory receptors.

      • Reticular Layer: Makes up 80% of dermal thickness with collagen and elastic fibers providing strength and elasticity.

Hypodermis

  • Subcutaneous Layer:

    • Anchors skin to underlying structures like muscles;

    • Composed of adipose and areolar connective tissue;

    • Functions as a shock absorber and insulator.

Skin Color

  • Pigments Contributing to Skin Color:

    • Melanin: Gives yellow to reddish-brown to black hues;

      • Produced in melanocytes and protects DNA in skin cells.

    • Carotene: Yellow to orange pigment mainly in palms and soles.

    • Hemoglobin: Reddish pigment that contributes to skin's color, particularly during circulation.

Appendages of Skin

  • Derivatives include sweat glands, oil glands, hairs, hair follicles, and nails.

Sweat Glands

  • Eccrine: Most common, primarily for thermoregulation, located on palms, soles, and forehead.

    • Sweat composition: 99% water, salts, and metabolic wastes.

  • Apocrine: Located in axillary and anogenital areas, contain fatty substances and proteins; become active during puberty.

Oil (Sebaceous) Glands

  • Produce oil (sebum) for skin and hair lubrication;

  • Help in waterproofing the skin;

  • Most distributed but absent in palms and soles.

Hair

  • Made of dead keratinized cells with hard keratin;

    • Comprised of shaft (projecting) and root (embedded); pigmentation comes from melanocytes.

Hair Follicle

  • Extends from epidermis to dermis, contains a hair bulb and sensory nerve endings;

  • Includes an arrector pili muscle giving rise to goosebumps.

Hair Types

  • Vellus: Fine, pale body hair;

  • Terminal: Coarse longer hair found in specific regions.

Nails

  • Composed of a nail plate, free edge, and nail fold;

  • The matrix is the area of nail growth.

Functions of Integumentary System

  1. Protection: Acts as a barrier against pathogens.

  2. Temperature Regulation: Via blood vessels and sweat secretion.

  3. Cutaneous Sensation: Using exoreceptors for touch and pain.

  4. Metabolic Functions: Synthesizes vitamin D.

  5. Blood Reservoir: Stores blood volume.

  6. Excretion: Elimination of waste through sweat.

Skin Cancer Types

  • Basal Cell Carcinoma: Most common form arising from stratum basale; high cure rate with surgery.

  • Squamous Cell Carcinoma: Arises from keratinocytes; good prognosis if treated early.

  • Melanoma: Most dangerous type; includes characteristics based on the ABCDE rule (Asymmetry, Border, Color, Diameter, Elevation).

Burns Classification

  • First-degree: Affects only the epidermis (redness and pain).

  • Second-degree: Affects epidermis and upper dermis (blisters).

  • Third-degree: Destroys all skin layers, requires medical treatment.

Rule of Nines

  • Used to estimate burn severity with specific body surface areas accounted for critical calculation.

Developmental Aspects

  • Fetal: Epidermis from ectoderm; dermis from mesoderm.

  • Adolescent to Adult: Increased sebaceous gland activity, oily skin.

  • Old Age: Slowed epidermal replacement, thinner skin, decreased fat and elasticity, increased cancer risk.