Human Skin Functions and Thermoregulation

Skin Functions

• Provides a physical barrier against thermal and mechanical insults, pathogens, and excessive water loss or uptake
• Protects cell nuclei from UV radiation through melanin in the epidermis
• Allows selective permeability for lipophilic drugs and hormones through skin patches
• Monitors the environment through sensory receptors and mechanoreceptors
• Synthesizes vitamin D3 through UV light for calcium metabolism and bone formation

Thermoregulation

• Controls heat transfer across the body's surface, facilitating heat retention and dissipation
• Sweat glands are vital for thermoregulation, and evaporating sweat can cool skin below core temperature
• Normal thermoregulatory sweating is often insensible, with sweat evaporating quickly

Additional Functions

• Releases visual and pheromonal signals, such as blushing and body odor
• Plays a crucial role in wound healing, with cells responding quickly to damage and regeneration
• Epithelial replacement can spread from deep hair follicles and sweat glands if the surface epidermis is damaged

Epidermis

• Consists primarily of keratinocytes with intercellular junctions (desmosomes) and intercellular channels for nutrient diffusion
• Keratinocytes are characterized by numerous desmosomes, visible as fine "prickles" between adjacent cells

Skin Color

• Skin is moderately transparent, with light penetrating and being reflected back from epidermal cells, collagen, and blood
• Melanin contributes a yellow/brown color to the epidermis, while collagen scatters light without altering its color
• Hemoglobin in red blood cells scatters red light, responsible for the pinkness of unpigmented skin