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 square meters. It serves as the primary interface between the body and the external environment, providing essential protection and regulatory functions.

• Cutaneous membrane (skin):

  • Epidermis – the superficial layer, composed of keratinizing stratified squamous epithelium.

  • Dermis/Hypodermis – deeper layers made up of connective tissues.

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

The integumentary system acts as the body's first line of defense against external threats such as pathogens, physical trauma, and environmental hazards.

Functions of the Integumentary System

The integumentary system performs several vital functions necessary for maintaining homeostasis and overall health.

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

  • Acts as a barrier to water loss and ultraviolet (UV) light.

  • Production of keratin (a tough, protective protein) and melanin (a pigment that absorbs UV radiation).

• Vitamin D3 Synthesis: Initiates the synthesis of vitamin D3 when exposed to UV light, which is essential for normal calcium metabolism and bone health.

• Sensory Reception: Contains specialized receptors for detecting pain, pressure, texture, and temperature, allowing the body to respond to environmental stimuli.

• Thermoregulation:

  • Vasoconstriction and vasodilation of blood vessels in the skin help regulate body temperature.

  • Sweating facilitates heat loss through evaporation.

• Nonverbal Communication: Facial expressions and skin color changes (e.g., blushing) are important for social interaction.

Key Terms and Concepts

• Epidermis: The outermost layer of skin, providing a waterproof barrier and contributing to skin tone.

• Dermis: The layer beneath the epidermis, containing tough connective tissue, hair follicles, and sweat glands.

• Hypodermis: Also known as the subcutaneous layer, it consists mainly of fat and connective tissue.

• Keratin: A fibrous protein that strengthens skin, hair, and nails.

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

• Vitamin D3: A vitamin synthesized in the skin that is crucial for calcium absorption and bone health.

Example: Vitamin D3 Synthesis

When the skin is exposed to ultraviolet B (UVB) radiation, 7-dehydrocholesterol in the epidermis is converted to cholecalciferol (vitamin D3). This process is essential for maintaining healthy bones and calcium metabolism.

Equation:

$\text{7-dehydrocholesterol} \xrightarrow{UVB} \text{cholecalciferol (Vitamin D}_3\text{)}$

Additional info:

• The hypodermis is not always considered part of the skin but is functionally important for insulation and energy storage.

• Accessory structures such as hair and nails are derived from the epidermis and serve protective and sensory roles.