5.5 Skin: Structure, Functions, and Heat Regulation

1. Structure of Skin

• Epidermis: Outermost layer.
  • Description: Stratified squamous epithelium, constantly regenerating, no blood vessels.
  • Functions: Protection (waterproof barrier, pathogens, UV), skin tone (melanin), Vitamin D synthesis.
• Dermis: Middle layer.
  • Description: Tough connective tissue (collagen, elastin), rich in blood vessels, nerves, hair follicles, glands.
  • Functions: Strength, elasticity, sensation, nourishment.
• Hypodermis (Subcutaneous Layer): Deepest layer.
  • Description: Loose connective tissue, adipose (fat) tissue.
  • Functions: Insulation, energy storage, cushioning, attachment.

1.2 Overall Functions of the Skin

• Protection: First line of defense (physical, chemical, pathogens, UV).
• Sensation: Perception of touch, pressure, temperature, pain.
• Thermoregulation: Regulates body temperature (sweating, blood flow).
• Excretion: Eliminates small amounts of waste (salts, urea) through sweat.
• Absorption: Limited absorption of certain substances.

2. Special Derivatives of the Skin

• Sweat Glands (Sudoriferous Glands): Produce sweat for cooling (eccrine) or odor (apocrine).
• Sebaceous Glands: Produce sebum (oil) to lubricate hair/skin, antibacterial.
• Hair: Protein filaments; insulation, protection, sensory perception.
• Nails: Hard, keratinized plates; protect digits, aid in grasping.
• Mammary Glands: Modified sweat glands; produce milk (in females).

3. Heat Regulation

• Skin plays a critical role in maintaining core body temperature.

Vasodilation

• Process: Blood vessels in dermis widen.
• Effect: Increases blood flow to skin surface, dissipates heat (radiation, convection), facilitates sweating.
• Occurs: When body temperature rises (e.g., exercise, hot environment).

3. Heat Regulation (Continued)

Vasoconstriction

• Process: Blood vessels in dermis narrow.
• Effect: Reduces blood flow to skin surface, minimizes heat loss, conserves body heat.
• Occurs: When body temperature drops (e.g., cold environment).

Summary

• Skin's layers and derivatives work together.
• Vasodilation and vasoconstriction are key mechanisms for thermoregulation.
• These processes, along with sweating and shivering, maintain optimal body temperature.