Chapter 5: The Integumentary System – Structure, Function, and Clinical Impact

Official Chapter 5 Integumentary System

Overview

The integumentary system is the body's largest organ system, primarily composed of the skin and its accessory structures. It serves as the first line of defense against environmental hazards and plays a vital role in maintaining homeostasis.

Functions of the Integumentary System

Main Functions

• Protection: Shields underlying tissues from mechanical damage, pathogens, and UV radiation.

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

• Temperature Regulation: Regulates body temperature through sweat production and blood flow.

• Vitamin D Production: Synthesizes vitamin D when exposed to sunlight, essential for calcium absorption.

• Excretion: Removes waste products through sweat.

Skin Structure

Major Layers of Skin

The skin, also known as the cutaneous membrane, consists of two primary layers:

• Epidermis: The outermost layer, composed of epithelial cells.

• Dermis: The deeper connective tissue layer.

Epidermis

• Cell Types:

  • Keratinoctyes: Produce keratin, a protein that provides strength and waterproofing.

  • Melanocytes: Produce melanin, the pigment responsible for skin color and UV protection.

  • Langerhans Cells: Immune cells involved in defense against pathogens.

  • Merkel Cells: Sensory cells associated with touch.

• Layers (Strata) of the Epidermis: Thin skin has 4 layers; thick skin (palms, soles) has 5 layers:

  • Stratum basale (germinativum): Deepest layer, site of cell division.

  • Stratum spinosum: Provides strength and flexibility.

  • Stratum granulosum: Contains granules for waterproofing.

  • Stratum lucidum: Present only in thick skin; provides extra protection.

  • Stratum corneum: Outermost layer; dead, keratinized cells.

Thick and Thin Skin

• Thick Skin: Found on palms and soles; contains all five strata.

• Thin Skin: Covers most of the body; lacks stratum lucidum.

Skin Color

Skin color results from the interaction of pigments and blood supply:

• Carotene: Yellow-orange pigment from diet.

• Melanin: Brown-black pigment produced by melanocytes.

• Dermal Blood Supply: Oxygenated blood gives a pinkish hue.

Dermis

• Papillary Layer: Superficial layer; contains capillaries and sensory receptors.

• Reticular Layer: Deep layer; provides strength and elasticity.

• Cleavage Lines: Patterns of collagen fibers; important for surgical incisions.

Subcutaneous Tissue (Hypodermis)

Structure and Function

• Location: Deep to the skin, beneath the dermis.

• Functions: Insulates the body, stores energy (fat), anchors skin to underlying tissues.

Accessory Skin Structures

Hair

• Types: Vellus (peach fuzz) and terminal hair (scalp, eyebrows, etc.).

Glands

• Sebaceous Glands: Secrete sebum (oil) to lubricate skin and hair.

• Sudoriferous (Sweat) Glands: Regulate temperature and excrete waste.

• Mammary Glands: Specialized sweat glands that produce milk.

• Ceruminous Glands: Produce earwax in the ear canal.

Nails

• Location: Found on the tips of fingers and toes.

• Function: Protects distal phalanges, aids in grasping objects.

Physiology of the Integumentary System

Protection

• Mechanical protection for underlying tissues.

• Prevents entry of pathogens.

• Melanin protects against UV damage.

• Hair and nails provide additional protective measures.

• Reduces water loss from the body.

Sensation

• Detects touch, pressure, pain, and temperature via specialized receptors.

Temperature Regulation

• Sweat glands release sweat to cool the body.

• Blood vessels in the dermis dilate or constrict to regulate heat loss.

Vitamin D Production

• UV light converts a precursor molecule in the skin to vitamin D.

• Vitamin D is essential for calcium absorption and bone health.

Excretion

• Removes small amounts of waste products (e.g., urea, salts) through sweat.

Clinical Impact: Skin Cancer

Types of Skin Cancer

• Basal Cell Carcinoma: Most common, arises from stratum basale, rarely metastasizes.

• Squamous Cell Carcinoma: Originates from stratum spinosum, may metastasize.

• Melanoma: Most dangerous, arises from melanocytes, high risk of metastasis.

ABCDE Rule for Melanoma Detection

• Asymmetry: One half of the mole does not match the other.

• Border: Edges are irregular, ragged, or blurred.

• Color: Varies from one area to another; shades of brown, black, or tan.

• Diameter: Larger than 6 mm (about the size of a pencil eraser).

• Evolving: Changes in size, shape, or color over time.

Example: A patient notices a mole that has changed color and shape over several months. Using the ABCDE rule, the mole is evaluated for asymmetry, irregular borders, multiple colors, increased diameter, and evolution, indicating a need for medical assessment.