Study Guide: The Integumentary System – Structure, Function, and Clinical Aspects

Introduction to the Integumentary System

Overview of the Integumentary System

The integumentary system is a complex organ system that includes the skin, hair, nails, and associated glands. It serves as the body's primary barrier against environmental hazards and plays a vital role in protection, sensation, thermoregulation, and synthesis of vitamin D.

• Key Structures: Epidermis, dermis, hypodermis, hair, nails, sebaceous and sweat glands.

• Main Functions: Protection, regulation of body temperature, sensory reception, excretion, and synthesis of vitamin D.

Section 5-1: The Epidermis – Structure and Function

Layers and Cell Types of the Epidermis

The epidermis is the outermost layer of the skin, composed of stratified squamous epithelium. It consists of several layers, each with specialized cells and functions.

• Classification of Epidermal Epithelium: Stratified squamous epithelium (keratinized).

• Function: Provides a protective barrier against mechanical injury, pathogens, and water loss.

• Layers of the Epidermis:

  1. Stratum basale (deepest)

  2. Stratum spinosum

  3. Stratum granulosum

  4. Stratum lucidum (only in thick skin)

  5. Stratum corneum (outermost)

• Thick vs. Thin Skin: Thick skin (palms, soles) contains all five layers; thin skin (most of the body) lacks stratum lucidum.

• Cell Types:

  • Keratinocytes: Main cell type, produce keratin for strength and waterproofing.

  • Melanocytes: Produce melanin pigment for UV protection.

  • Langerhans cells: Immune cells (dendritic cells) involved in defense.

  • Merkel cells: Sensory receptors for touch.

• Specialized Structures: Epidermal ridges (fingerprints) increase grip and surface area.

Example: The stratum corneum is thickest on the palms and soles, providing extra protection against abrasion.

Section 5-2: The Dermis – Structure and Function

Layers and Properties of the Dermis

The dermis lies beneath the epidermis and provides structural support, elasticity, and nourishment to the skin. It contains connective tissue, blood vessels, nerves, and accessory structures.

• Layers of the Dermis:

  1. Papillary layer: Superficial, composed of loose areolar connective tissue; forms dermal papillae.

  2. Reticular layer: Deep, composed of dense irregular connective tissue; provides strength and elasticity.

• Functions: Supports epidermis, houses sensory receptors, regulates temperature, and supplies nutrients.

• Dermal Strength and Elasticity: Provided by collagen and elastic fibers.

• Scarring: Scars form when the skin heals after injury; orientation of fibers affects appearance.

• Subcutaneous Layer (Hypodermis): Connects skin to underlying tissues, stores fat, and insulates the body.

Example: Stretch marks occur when the dermis is stretched beyond its elastic limits, causing tears in collagen fibers.

Section 5-3: Accessory Structures – Hair and Nails

Hair Structure and Function

Hair is a keratinized structure produced by hair follicles. It serves protective, sensory, and thermoregulatory functions.

• Parts of Hair: Shaft (visible), root (embedded), follicle (surrounds root).

• Hair Growth: Occurs in cycles: anagen (growth), catagen (regression), telogen (resting).

• Hair Types: Vellus (fine, unpigmented), terminal (thick, pigmented).

• Hair Color: Determined by melanin type and amount.

• Clinical Note: Baldness (alopecia) can be caused by genetics, hormones, or disease.

Nail Structure and Function

• Nails: Hard keratinized plates protecting the distal phalanges.

• Parts of Nail: Nail plate, nail bed, matrix (growth area), cuticle (eponychium), lunula (white crescent).

• Growth: Occurs at the nail matrix; rate varies with age and health.

Example: Clubbing of nails may indicate chronic hypoxia or lung disease.

Section 5-4: Skin Color – Pigmentation and Circulation

Determinants of Skin Color

Skin color is influenced by genetic, environmental, and physiological factors. The main pigments are melanin, carotene, and hemoglobin.

• Melanin: Produced by melanocytes; protects against UV radiation.

• Carotene: Yellow-orange pigment from diet; stored in skin.

• Hemoglobin: Red pigment in blood; gives skin a pinkish hue.

• Disorders: Albinism (lack of melanin), vitiligo (loss of pigment in patches).

• Clinical Signs:

  • Cyanosis: Bluish skin due to low oxygen.

  • Jaundice: Yellow skin due to bilirubin buildup.

  • Addison's disease: Bronze skin due to adrenal dysfunction.

  • Tumor of the pituitary gland: May cause abnormal pigmentation.

Example: Increased melanin production after sun exposure leads to tanning.

Section 5-5: Sunlight and Vitamin D Synthesis

Role of Sunlight in Skin Physiology

Exposure to sunlight enables the skin to synthesize vitamin D, which is essential for calcium absorption and bone health.

• Vitamin D Synthesis: UV radiation converts 7-dehydrocholesterol in the skin to cholecalciferol (vitamin D3).

• Importance: Prevents rickets, osteomalacia, and supports immune function.

• Deficiency: Can lead to bone disorders and increased risk of chronic diseases.

Example: Individuals with limited sun exposure may require dietary supplementation of vitamin D.

Section 5-6: Keratinization and Skin Protection

Keratinized Structures and Their Functions

Keratinization is the process by which cells become filled with keratin protein, providing strength and waterproofing to the skin, hair, and nails.

• Keratin: Fibrous protein that protects against abrasion and water loss.

• Stratum corneum: Layer of dead, keratinized cells forming the skin's outer barrier.

• Accessory Structures: Hair, nails, and glands are derived from epidermal cells.

Example: Calluses form in response to repeated friction, increasing keratin production.

Section 5-7: Glands of the Skin

Sebaceous and Sweat Glands

The skin contains several types of glands that contribute to lubrication, thermoregulation, and protection.

• Sebaceous Glands: Produce sebum, an oily substance that lubricates skin and hair.

• Sudoriferous (Sweat) Glands:

  • Eccrine glands: Widely distributed, produce watery sweat for cooling.

  • Apocrine glands: Found in axillae and groin, produce thicker secretion; active after puberty.

• Other Glands: Ceruminous glands (earwax), mammary glands (milk).

• Thermoregulation: Sweat evaporation helps regulate body temperature.

Example: Overactive sebaceous glands can lead to acne formation.

Section 5-8: Nails – Structure and Growth

Structure and Function of Nails

Nails are protective keratinized structures at the tips of fingers and toes. They aid in grasping objects and protect the distal phalanges.

• Parts of the Nail: Nail plate, nail bed, matrix, cuticle (eponychium), lunula.

• Growth: Occurs at the nail matrix; rate is affected by age, nutrition, and health.

• Common Disorders: Onychomycosis (fungal infection), clubbing, spoon nails (koilonychia).

Example: Nail growth is faster in younger individuals and slows with age.

Section 5-9: Skin Repair and Healing

Phases of Skin Repair

After injury, the skin undergoes a series of phases to restore its integrity. The process involves inflammation, tissue formation, and remodeling.

• Phases of Repair:

  1. Inflammation

  2. Migratory phase

  3. Proliferation phase

  4. Maturation (remodeling) phase

• Scarring: Occurs when collagen fibers replace normal tissue.

• Burns: Classified by depth and surface area; treatment depends on severity.

• Clinical Note: The "rule of nines" is used to estimate burn surface area.

Example: Second-degree burns affect both the epidermis and part of the dermis, causing blistering.

Section 5-10: Effects of Aging on the Skin

Age-Related Changes

Aging leads to thinning of the skin, reduced elasticity, decreased melanocyte activity, and increased wrinkling.

• Thinning: Epidermis and dermis become thinner, increasing risk of injury.

• Wrinkling: Loss of collagen and elastic fibers.

• Reduced Melanocyte Activity: Leads to paler skin and increased risk of sun damage.

Example: Elderly individuals are more prone to skin tears and pressure ulcers.

Key Table: Layers of the Epidermis

Layer	Location	Main Cell Type	Function
Stratum basale	Deepest	Keratinocytes, melanocytes	Cell division, pigment production
Stratum spinosum	Above basale	Keratinocytes, Langerhans cells	Strength, immune defense
Stratum granulosum	Middle	Keratinocytes	Keratin formation, waterproofing
Stratum lucidum	Thick skin only	Keratinocytes	Extra protection
Stratum corneum	Outermost	Dead keratinocytes	Barrier, protection

Key Equations and Definitions

• Rule of Nines (Burn Assessment): Used to estimate the percentage of body surface area affected by burns.

• Vitamin D Synthesis: $\text{7-dehydrocholesterol} + UV \rightarrow \text{cholecalciferol (Vitamin D}_3)$

• Melanin Production: $\text{Tyrosine} \xrightarrow{Tyrosinase} \text{Melanin}$

Additional info: Some content was expanded for clarity and completeness, including definitions, examples, and clinical notes.