Study Guide: The Integumentary System – Anatomy & Physiology

Introduction to the Integumentary System

Overview of the Integumentary System

The integumentary system is the body's largest organ system, primarily consisting of the skin, hair, nails, and associated glands. It serves as a protective barrier, regulates temperature, and provides sensory information.

• Key Structures: Epidermis, dermis, hypodermis, hair, nails, glands

• Main Functions: Protection, sensation, thermoregulation, vitamin D synthesis

Section 5-1: The Epidermis

Structure and Function of the Epidermis

The epidermis is the outermost layer of the skin, composed of stratified squamous epithelial cells. It provides a barrier against environmental damage and pathogens.

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

• Layers of the Epidermis: (from superficial to deep)

  1. Stratum corneum

  2. Stratum lucidum (only in thick skin)

  3. Stratum granulosum

  4. Stratum spinosum

  5. Stratum basale

• Thick vs. Thin Skin: Thick skin (palms, soles) contains all five layers; thin skin 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) for defense.

  • Merkel cells: Sensory receptors for touch.

• Hemidesmosomes: Structures that anchor epidermal cells to the basement membrane.

• Basal Cells: Stem cells in the stratum basale that divide to produce new keratinocytes.

• Water Resistance: Epidermis limits water loss and absorption, maintaining homeostasis.

Additional info: Epidermal ridges (fingerprints) increase grip and surface area for attachment to the dermis.

Section 5-2: The Dermis

Structure and Function of the Dermis

The dermis is a connective tissue layer beneath the epidermis, providing strength, elasticity, and support for skin appendages.

• Layers of the Dermis:

  1. Papillary layer: Superficial, contains loose connective tissue and capillaries.

  2. Reticular layer: Deep, dense irregular connective tissue with collagen and elastic fibers.

• Dermal Strength and Elasticity: Provided by collagen (strength) and elastic fibers (flexibility).

• Lines of Cleavage (Langer's lines): Patterns of collagen fiber orientation; incisions parallel to these lines heal better.

• Scarring: Greater when cuts are perpendicular to cleavage lines.

• Dermal Papillae: Projections that interlock with epidermal ridges, increasing surface area.

Section 5-3: The Hypodermis (Subcutaneous Layer)

Structure and Function of the Hypodermis

The hypodermis is a layer of loose connective tissue and fat beneath the dermis, connecting skin to underlying structures and providing insulation and energy storage.

• Composition: Adipose tissue, areolar connective tissue

• Functions: Insulation, shock absorption, energy reserve

• Distribution: Varies by body region, sex, and age

Section 5-4: Skin Color and Pigmentation

Determinants of Skin Color

Skin color is influenced by genetic, environmental, and physiological factors, primarily due to the presence of pigments.

• Main Pigments:

  • Melanin: Produced by melanocytes; determines brown-black coloration.

  • Carotene: Yellow-orange pigment from diet (e.g., carrots).

  • Hemoglobin: Red pigment in blood, visible in fair skin.

• Albinism: Genetic condition with lack of melanin production.

• Skin Color Changes:

  • Cyanosis: Bluish skin due to low oxygen.

  • Jaundice: Yellow skin due to liver dysfunction.

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

  • Tumor of the pituitary gland: May affect pigmentation.

• Vitamin D Synthesis: UV exposure stimulates production in the skin.

Section 5-5: Sunlight and Vitamin D

Role of Sunlight in Vitamin D Synthesis

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

• Cholecalciferol (Vitamin D3): Produced in the skin from 7-dehydrocholesterol upon UV exposure.

• Vitamin D Deficiency: Leads to abnormal bone development (rickets, osteomalacia).

• Clinical Note: Sunburns are caused by excessive UV exposure, leading to skin damage.

• Skin Cancer: Types include basal cell carcinoma, squamous cell carcinoma, and melanoma (most dangerous).

• ABCDE Rule: Used to assess moles for melanoma:

  • A: Asymmetry

  • B: Border irregularity

  • C: Color variation

  • D: Diameter > 6mm

  • E: Evolving shape/size

Section 5-6: The Hair and Hair Follicles

Structure and Function of Hair

Hair is composed of keratinized cells produced by hair follicles, providing protection, sensation, and thermoregulation.

• Hair Structure:

  • Shaft: Visible part above skin

  • Root: Embedded in follicle

  • Bulb: Base of follicle where growth occurs

• Hair Layers: Medulla (core), cortex (middle), cuticle (outer)

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

• Hair Types: Vellus (fine), terminal (thick)

• Hair Color: Determined by melanin type and amount

• Hair Shape: Follicle shape determines straight or curly hair

Section 5-7: Sebaceous and Sweat Glands

Types and Functions of Skin Glands

The skin contains several types of exocrine glands that produce secretions for lubrication, protection, and thermoregulation.

• Sebaceous Glands: Produce sebum (oil) for lubrication; associated with hair follicles.

• Sudoriferous (Sweat) Glands:

  • Merocrine (Eccrine): Widely distributed, produce watery sweat for cooling.

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

• Mammary Glands: Modified sweat glands for milk production.

• Ceruminous Glands: Produce earwax (cerumen).

• Thermoregulation: Sweat evaporation cools the body; homeostatic feedback mechanisms regulate this process.

Section 5-8: Nails

Structure and Function of Nails

Nails are keratinized epidermal cells that protect the tips of fingers and toes and aid in manipulation.

• Main Structures: Nail plate, nail bed, nail matrix (growth area), cuticle (eponychium), hyponychium

• Growth: Occurs at the nail matrix

• Common Disorders: Onychomycosis (fungal infection), paronychia (infection of nail fold)

Section 5-9: Integument Repair and Burns

Skin Repair and Burn Classification

After injury, the skin undergoes a series of phases to repair itself. Burns are classified by depth and surface area affected.

• Phases of Repair:

  1. Inflammation

  2. Migratory phase

  3. Proliferation phase

  4. Scarring (maturation) phase

• Tattoo Removal: Permanent ink removal requires destruction of pigment in the dermis.

• Burn Classification:

  • First-degree: Epidermis only

  • Second-degree: Epidermis and part of dermis

  • Third-degree: Full thickness (epidermis, dermis, possibly deeper)

• Rule of Nines: Used to estimate surface area affected by burns.

Section 5-10: Effects of Aging on the Skin

Age-Related Changes in the Integumentary System

Aging leads to thinning of the skin, wrinkling, and reduced activity of melanocytes, affecting protection and appearance.

• Thinning: Epidermis and dermis become thinner

• Wrinkling: Loss of collagen and elastic fibers

• Reduced Melanocyte Activity: Increased risk of UV damage

Table: Comparison of Epidermal Layers

Layer	Location	Main Cell Type	Function
Stratum corneum	Superficial	Keratinocytes (dead)	Protection, water resistance
Stratum lucidum	Thick skin only	Keratinocytes (dead)	Extra protection
Stratum granulosum	Middle	Keratinocytes	Keratin formation
Stratum spinosum	Middle	Keratinocytes, Langerhans cells	Strength, immune defense
Stratum basale	Deepest	Basal cells, melanocytes, Merkel cells	Cell division, pigment production, sensation

Key Equations

• Rule of Nines (Burn Surface Area Estimation): $\text{Total Body Surface Area Burned} = \sum \text{(Area % for each region affected)}$

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