Integumentary System: Structure, Function, and Clinical Considerations

Integumentary System

Overview

The integumentary system is a complex organ system that serves as the body's primary interface with the external environment. It consists of the skin and its associated appendages, providing protection, sensation, and regulatory functions.

• Skin (cutaneous membrane): The largest organ of the body, forming a protective barrier.

• Skin appendages:

  • Sweat glands

  • Oil (sebaceous) glands

  • Hair

  • Nails

Functions of the Integumentary System

Protective and Regulatory Roles

The integumentary system performs several vital functions to maintain homeostasis and protect the body.

• Insulation and cushioning: Protects deeper organs from physical trauma.

• Protection from damage:

  • Mechanical (bumps, cuts)

  • Chemical (acids, bases)

  • Thermal (heat, cold)

  • Ultraviolet (UV) radiation

  • Microbial invasion (bacteria)

  • Water loss (desiccation)

• Regulation of heat loss: Controlled by the nervous system via blood flow and sweat production.

• Excretion: Sweat glands aid in the removal of urea, salts, and water.

• Synthesis of vitamin D: Modified cholesterol molecules in the skin are converted to vitamin D in the presence of sunlight.

• Acid mantle: Secretions create a slightly acidic environment that inhibits bacterial growth.

Table: Functions of the Integumentary System

Function	How Accomplished
Protects deeper tissues	Keratinized cells form a physical barrier; pressure and pain receptors alert the nervous system.
Mechanical damage	Cushioning by fat cells; keratin toughens cells.
Chemical damage	Impermeable keratinized cells; acid mantle neutralizes chemicals.
Microbe damage	Acid mantle and immune cells prevent pathogen entry.
UV radiation	Melanin produced by melanocytes absorbs UV light.
Thermal damage	Heat/cold/pain receptors detect temperature extremes.
Desiccation	Water-resistant glycolipids and keratin prevent water loss.
Heat loss/retention	Sweat glands and blood flow regulation by the nervous system.
Excretion	Sweat glands remove urea and uric acid.
Vitamin D synthesis	Sunlight converts skin cholesterol to vitamin D.

Structure of the Skin

Layers and Composition

The skin is composed of two main layers and an underlying supportive tissue.

• Epidermis:

  • Outer layer

  • Stratified squamous epithelium

  • Keratinocytes produce keratin, a tough, protective protein

  • Desmosomes connect keratinocytes

  • Avascular (no blood vessels)

  • Composed of five strata (layers)

• Dermis:

  • Connective tissue layer beneath the epidermis

  • Two regions: papillary and reticular

• Subcutaneous tissue (hypodermis):

  • Anchors skin to underlying organs

  • Mostly adipose tissue

  • Shock absorber and insulator

  • Not technically part of the integumentary system

Layers of the Epidermis

The epidermis consists of five distinct layers, each with specialized functions.

1. Stratum basale (germinativum):

   • Deepest layer, adjacent to dermis

   • Cells undergo mitosis

   • Wavy border anchors epidermis to dermis

2. Stratum spinosum:

   • Cells become flatter and more keratinized

3. Stratum granulosum:

   • Cells contain granules; further keratinization

4. Stratum lucidum:

   • Present only in thick, hairless skin (palms, soles)

   • Formed from dead cells of deeper strata

5. Stratum corneum:

   • Outermost layer

   • Shingle-like dead cells filled with keratin

   • Protects against water loss

Specialized Epidermal Cells

• Melanocytes: Produce melanin pigment (yellow to black) in the stratum basale.

• Epidermal dendritic cells: Activate immune responses to pathogens.

• Merkel cells: Associated with sensory nerve endings; function as touch receptors (Merkel discs).

Dermis Structure

• Papillary layer:

  • Areolar connective tissue

  • Dermal papillae project into epidermis

  • Contain capillary loops, pain, and touch receptors

  • Increase friction and grip (fingerprints)

• Reticular layer:

  • Dense irregular connective tissue

  • Contains blood vessels, sweat and oil glands, deep pressure receptors (lamellar corpuscles)

• Other dermal features:

  • Cutaneous sensory receptors

  • Phagocytes

  • Collagen and elastic fibers

  • Blood vessels

  • Nerve supply

Skin Color

Pigments and Clinical Indicators

Skin color is determined by three main pigments and can indicate underlying health conditions.

• Melanin: Yellow, reddish brown, or black pigment produced by melanocytes.

• Carotene: Orange-yellow pigment found in vegetables and skin.

• Hemoglobin: Red pigment in blood; oxygenation level affects skin redness.

Clinical Color Changes

• Redness (erythema): May indicate inflammation, fever, allergy, or hypertension.

• Pallor (blanching): Associated with stress, anemia, or impaired blood flow.

• Jaundice: Yellow cast, often due to liver disorders.

• Bruises (hematomas): Black and blue marks from blood leakage under the skin.

Appendages of the Skin

Cutaneous Glands

• Exocrine glands:

  • Sebaceous (oil) glands:

    • Produce sebum to lubricate skin and hair

    • Kill bacteria

    • Activated at puberty by androgens

    • Absent on palms and soles

  • Sweat (sudoriferous) glands:

    • Produce sweat for thermoregulation and excretion

    • Two types: Eccrine glands (widely distributed, open to skin surface, produce acidic sweat) and Apocrine glands (empty into hair follicles in armpit/genitals, begin at puberty, secrete sweat with fatty acids and proteins)

Hair and Hair Follicles

• Hair:

  • Produced by hair follicles

  • Root enclosed in follicle; shaft projects from skin

  • Composed of hard keratinized epithelial cells

  • Melanocytes provide pigment

  • Growth occurs in matrix of hair bulb (stratum basale)

• Hair anatomy:

  • Central medulla

  • Cortex surrounds medulla

  • Cuticle (outermost, most keratinized)

• Associated structures:

  • Hair follicle: inner epithelial root sheath, outer fibrous sheath

  • Dermal region supplies blood to hair bulb

  • Arrector pili muscle: contracts to raise hair (goosebumps)

Nails

• Structure:

  • Heavily keratinized, scalelike modifications of epidermis

  • Stratum basale extends beneath nail bed (growth region)

  • Lack of pigment makes nails colorless

• Parts of a nail:

  • Free edge

  • Body (visible attached portion)

  • Nail folds (skin overlaps edges; cuticle is proximal edge)

  • Root (embedded in skin)

  • Growth from nail matrix of nail bed

Homeostatic Imbalances of Skin

Infections and Allergies

• Athlete's foot: Fungal infection (Tinea pedis); causes itchy, red, peeling skin between toes.

• Boils and carbuncles: Inflammation of hair follicles; carbuncles are clusters of boils caused by bacteria.

• Cold sores: Caused by human herpesvirus 1; blisters that itch and sting.

• Contact dermatitis: Allergic response to chemicals; causes itching, redness, swelling.

• Impetigo: Bacterial infection; pink, fluid-filled raised lesions around mouth/nose.

• Psoriasis: Chronic condition triggered by trauma, infection, hormonal changes, or stress; red, scaly lesions that may crack or bleed.

Burns

• Definition: Tissue damage and cell death caused by heat, electricity, UV radiation, or chemicals.

• Dangers: Protein denaturation, dehydration, electrolyte imbalance, circulatory shock, infection.

• Rule of nines: Body divided into 11 areas, each representing 9% of total body surface area; perineum is 1%.

• Burn degrees:

  • First-degree: Only epidermis damaged; skin red and swollen.

  • Second-degree: Epidermis and superficial dermis damaged; skin red, painful, blistered; regrowth possible.

  • Third-degree: Full-thickness; destroys epidermis and dermis; area is painless, requires grafts, appears gray-white or black.

  • Fourth-degree: Extends into deeper tissues; dry, leathery appearance; requires surgery/grafting, possible amputation.

Skin Cancer

• Most common cancer type in humans.

• Risk factor: Overexposure to UV radiation.

• Classification:

  • Benign: Tumor has not spread.

  • Malignant: Tumor has invaded other body areas.

• Types:

  • Basal cell carcinoma: Least malignant, most common; arises from stratum basale cells.

  • Squamous cell carcinoma: Induced by UV exposure; arises from stratum spinosum; can metastasize.

  • Malignant melanoma: Most deadly; cancer of melanocytes; rapid metastasis; diagnosed using ABCDE rule.

ABCDE Rule for Melanoma Detection

• A = Asymmetry: Two sides of mole do not match.

• B = Border irregularity: Borders are not smooth.

• C = Color: Multiple colors present.

• D = Diameter: Larger than 6 mm.

• E = Evolution: Changes in any of the above characteristics.

Additional info: The notes are based on textbook slides and include figures and tables for visual reference. All major topics of the integumentary system are covered, including structure, function, appendages, clinical conditions, and homeostatic imbalances.