Chapter 5: The Integumentary System – Structure and Function

Integumentary System

Overview of the Integument

The integumentary system is the largest organ system of the human body, accounting for approximately 16% of total body weight and covering an area of 1.5 to 2 m2. It serves as the primary interface between the body and the external environment, providing essential protection and support.

• Cutaneous membrane (skin): Composed of two main layers:

  • Epidermis: The superficial layer, made of keratinizing stratified squamous epithelium.

  • Dermis/Hypodermis: The deeper layers, consisting of connective tissues.

• Accessory structures: Includes hair, nails, and multicellular glands.

The integumentary system acts as the body’s first line of defense against environmental hazards.

Functions of the Integumentary System

The integumentary system performs several vital functions that contribute to overall health and homeostasis.

• Protection: Shields underlying tissues and organs from trauma and infection.

  • Acts as a barrier to water and ultraviolet (UV) light, aided by the production of keratin and melanin.

• Vitamin D3 Synthesis: Facilitates the production of vitamin D3 for normal calcium metabolism, which is essential for bone health.

• Sensory Reception: Detects pain, pressure, texture, and temperature through specialized sensory receptors embedded in the skin.

• Thermoregulation: Maintains body temperature via:

  • Vasoconstriction: Narrowing of blood vessels to reduce heat loss.

  • Vasodilation: Widening of blood vessels to increase heat dissipation.

  • Sweating: Evaporation of sweat cools the body.

• Nonverbal Communication: The skin and its appendages (such as facial hair and nails) play a role in social signaling and expression.

Key Terms and Definitions

• Epidermis: The outermost layer of skin, primarily responsible for protection and barrier functions.

• Dermis: The middle layer of skin, providing structural support and housing blood vessels, nerves, and glands.

• Hypodermis: The deepest layer, consisting mainly of adipose tissue for insulation and energy storage.

• Keratin: A tough, fibrous protein that strengthens the skin and makes it water-resistant.

• Melanin: A pigment produced by melanocytes that protects against UV radiation and determines skin color.

Example: Vitamin D3 Synthesis

When exposed to sunlight, the skin synthesizes vitamin D3 from 7-dehydrocholesterol. This vitamin is then converted in the liver and kidneys to its active form, calcitriol, which is crucial for calcium absorption in the intestines.

Additional info:

• The hypodermis, also known as the subcutaneous layer, is not always distinctly separated from the dermis but plays a key role in insulation and energy storage.

• Accessory structures such as hair and nails are derived from the epidermis during embryonic development.