Integumentary System: Structure, Function, and Clinical Relevance

Integumentary System

The integumentary system is the organ system that forms the external covering of the body, primarily consisting of the skin and its associated structures. It plays a vital role in protection, sensation, and homeostasis.

Functions of the Integumentary System

• Protection: Acts as a physical barrier against mechanical injury, pathogens, and harmful substances.

• Thermoregulation: Regulates body temperature through sweat production and blood flow adjustments.

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

• Excretion and Absorption: Excretes waste products (e.g., urea, salts) and absorbs certain chemicals and drugs.

• Synthesis of Vitamin D: Initiates the synthesis of vitamin D when exposed to ultraviolet (UV) light.

• Transdermal Drug Administration: Allows certain medications to be absorbed through the skin.

Key Facts:

• The skin accounts for approximately 16% of total body weight.

• Average weight: 9–11 pounds (4–5 kg).

• Thickness: ranges from 1.5 to 4 mm depending on location.

Skin Structure

The skin is composed of three main layers, each with distinct structures and functions.

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

• Dermis: The middle, thicker layer made of connective tissue, containing blood vessels, nerves, and accessory structures.

• Hypodermis (Subcutaneous Layer): Not technically part of the skin, this layer consists of areolar and adipose tissue, providing insulation, energy storage, and cushioning. It contains fat, blood vessels, and nerves.

Skin Accessory Structures

Accessory structures are primarily located in the dermis and include:

• Hair follicles

• Exocrine glands (e.g., sweat and sebaceous glands)

• Nails

Layers of the Epidermis

The epidermis is a stratified squamous epithelium composed of several distinct layers (from superficial to deep):

• Stratum corneum: Outermost layer of dead, keratinized cells providing a tough, protective barrier.

• Stratum lucidum: Thin, clear layer found only in thick skin (palms, soles).

• Stratum granulosum: Layer where keratinization begins; cells contain granules of keratohyalin.

• Stratum spinosum: Several layers of keratinocytes connected by desmosomes; provides strength and flexibility.

• Stratum basale (germinativum): Deepest layer; site of active cell division (mitosis) and contains melanocytes.

Example: The stratum lucidum is present in the thick skin of the palms and soles but absent in thin skin covering most of the body.

Additional info:

• Keratinization: The process by which keratinocytes produce keratin and move upward through the epidermal layers, eventually dying and forming the stratum corneum.

• Melanocytes: Specialized cells in the stratum basale that produce melanin, the pigment responsible for skin color.