Chapter 5: The Integumentary System – Comprehensive Study Notes

Integumentary System Overview

Components of the Integumentary System

• Skin: The largest organ of the body, consisting of two main layers (epidermis and dermis) and associated subcutaneous tissue.

• Hair: Filamentous structures composed of keratinized cells, distributed over most of the body.

• Nails: Hard, keratinized plates covering the dorsal surfaces of the distal phalanges.

• Glands: Includes sweat (sudoriferous) glands and sebaceous (oil) glands.

• Associated Nerves and Blood Vessels: Provide sensation and nourishment.

Additional info: The hypodermis (subcutaneous tissue) is not technically part of the skin but is closely associated with its structure and function.

Functions of the Skin

Main Functions and Detailed Descriptions

• Protection: Acts as a physical, chemical, and biological barrier against pathogens, chemicals, and physical trauma.

• Body Temperature Regulation: Sweat glands and blood vessel dilation/constriction help maintain homeostasis.

• Cutaneous Sensation: Contains sensory receptors for touch, pain, temperature, and pressure.

• Metabolic Functions: Synthesizes vitamin D precursor when exposed to UV light; aids in calcium absorption.

• Blood Reservoir: Stores up to 5% of the body’s blood volume in dermal vessels.

• Excretion: Eliminates nitrogenous wastes, salts, and water through sweat.

Structure of the Skin

Layers of the Skin

• Epidermis: Superficial, avascular layer composed of keratinized stratified squamous epithelium.

• Dermis: Deep, vascular layer of connective tissue containing nerves, blood vessels, and accessory structures.

• Subcutaneous Tissue (Hypodermis): Not part of the skin proper; consists mainly of adipose tissue and anchors skin to underlying structures.

Detailed Makeup and Cells of Each Layer

• Epidermis:

  • Composed of four or five layers (strata): stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only in thick skin), and stratum corneum.

  • Major cell types:

    • Keratinoctyes: Produce keratin, a protective protein.

    • Melanocytes: Synthesize melanin pigment.

    • Epidermal Dendritic (Langerhans) Cells: Immune defense.

    • Tactile (Merkel) Cells: Sensory receptors for touch.

  • Function: Provides a barrier, prevents water loss, and contributes to skin color.

• Dermis:

  • Two layers: papillary (areolar connective tissue) and reticular (dense irregular connective tissue).

  • Contains fibroblasts, macrophages, mast cells, and white blood cells.

  • Houses blood vessels, nerves, hair follicles, and glands.

  • Function: Provides strength, elasticity, and nourishment to the epidermis.

• Subcutaneous Tissue (Hypodermis):

  • Mainly adipose tissue; stores fat and anchors skin to muscles.

  • Function: Insulation, shock absorption, and energy storage.

Skin Pigments

Melanin, Carotene, and Hemoglobin

• Melanin:

  • Produced by melanocytes in the epidermis.

  • Color ranges from yellow to brown to black.

  • Protects DNA from UV radiation.

  • Homeostatic Imbalance: Overproduction can cause freckles or moles; underproduction leads to albinism.

• Carotene:

  • Yellow-orange pigment from diet (e.g., carrots, sweet potatoes).

  • Accumulates in stratum corneum and hypodermis.

  • Can be converted to vitamin A.

  • Homeostatic Imbalance: Excessive intake can cause carotenemia (yellowish skin).

• Hemoglobin:

  • Oxygen-carrying pigment in red blood cells.

  • Gives skin a pinkish hue, especially in fair-skinned individuals.

  • Homeostatic Imbalance: Cyanosis (bluish skin) indicates low oxygenation; erythema (redness) signals inflammation or fever.

Hair

Description and Structure

• Description: Flexible strands of dead, keratinized cells produced by hair follicles; found everywhere except palms, soles, lips, nipples, and parts of external genitalia.

• Structure:

  • Shaft: Visible part above the skin surface.

  • Root: Embedded in the skin.

  • Medulla: Central core (large cells and air spaces).

  • Cortex: Surrounds medulla; several layers of flattened cells.

  • Cuticle: Outermost layer; single layer of overlapping cells.

• Hair Follicle:

  • Extends from epidermis into dermis.

  • Bulb at base contains actively dividing cells (hair matrix).

  • Associated with arrector pili muscle (causes "goosebumps").

• Types of Hair Growth:

  • Anagen: Active growth phase.

  • Catagen: Transitional phase.

  • Telogen: Resting phase; hair eventually falls out.

• Hair Thinning and Baldness:

  • Alopecia: General term for hair thinning.

  • Male Pattern Baldness: Genetically determined, sex-influenced condition.

  • Homeostatic Imbalance: Can result from hormonal changes, stress, or disease.

Nails

Description, Structure, and Imbalances

• Description: Scale-like modifications of the epidermis; protect distal phalanges.

• Location: Dorsal surface of fingers and toes.

• Function: Protects tips of digits, aids in picking up objects, and enhances sensation.

• Structure:

  • Nail Plate: Visible attached part.

  • Nail Bed: Underlying epidermis.

  • Nail Matrix: Proximal region; site of nail growth.

  • Lunule: White crescent at base of nail.

  • Cuticle (Eponychium): Fold of skin at nail base.

• Homeostatic Imbalance: Disorders include fungal infections, clubbing (chronic hypoxia), and spoon nails (iron deficiency).

Sweat Glands

Description, Types, and Functions

• Description: Distributed over most of the body; secrete sweat for thermoregulation and excretion.

• Location: Most numerous on palms, soles, and forehead.

• Function: Regulate body temperature, excrete wastes, and provide some antibacterial action.

• Types:

  • Eccrine (Merocrine) Glands:

    • Most numerous; open directly onto skin surface.

    • Secrete watery, hypotonic sweat (99% water, salts, urea).

    • Function in thermoregulation.

  • Apocrine Glands:

    • Located in axillary and anogenital regions.

    • Secrete viscous, milky or yellowish sweat into hair follicles.

    • Begin functioning at puberty; responsible for body odor when decomposed by bacteria.

Sebaceous (Oil) Glands

Description, Location, Function, and Imbalances

• Description: Simple alveolar glands; secrete sebum (oily substance).

• Location: All over body except palms and soles; most abundant on face, neck, and upper chest.

• Function: Lubricates and waterproofs skin and hair; has antibacterial properties.

• Homeostatic Imbalance: Overactivity leads to acne; underactivity causes dry, cracked skin.

Skin Cancer

Types and Characteristics

• Basal Cell Carcinoma: Most common, least malignant; arises from stratum basale; slow-growing.

• Squamous Cell Carcinoma: Arises from keratinocytes of stratum spinosum; can metastasize if not removed.

• Melanoma: Cancer of melanocytes; highly metastatic and resistant to chemotherapy; most dangerous.

Burns

Classification by Severity

Degree	Layer Affected	Symptoms
First-degree	Epidermis only	Redness, swelling, pain (e.g., sunburn)
Second-degree	Epidermis and upper dermis	Blisters, redness, pain
Third-degree	Entire thickness of skin	Gray-white, cherry red, or blackened; no initial pain (nerve endings destroyed)

Additional info: Burns are critical if >25% of body has second-degree burns, >10% has third-degree burns, or if face, hands, or feet are involved.

Developmental Aspects of the Integumentary System

Embryo to Fetus

• Epidermis develops from ectoderm; dermis and hypodermis from mesoderm.

• By the fourth month, skin is well formed; lanugo (fine hair) covers fetus by fifth/sixth month.

Infancy to Adulthood

• Skin thickens and accumulates more subcutaneous fat.

• Glands become fully functional at puberty.

Aging Skin

• Epidermal replacement slows; skin becomes thinner, drier, and more prone to injury.

• Elasticity decreases; wrinkles form.

• Increased risk of skin cancer due to decreased melanocyte activity.