The Skin, Hair and Nails (Integumentary System)
The integumentary system domain tests skin layers, accessory structures, barrier and temperature functions, wound healing and burn assessment. Questions often require you to identify the layer involved in an injury or distinguish gland and hair types.
Core rules and concepts
- The epidermis is avascular keratinized stratified squamous epithelium. Its deepest layer contains stem cells; melanocytes produce melanin; keratinocytes produce keratin.
- The dermis contains collagen and elastin, blood vessels, nerves, glands and hair follicles. The hypodermis is subcutaneous fat and connective tissue that insulates and anchors the skin.
- Eccrine sweat glands are widespread and produce watery sweat for thermoregulation. Apocrine glands are associated with hair follicles and become active at puberty. Sebaceous glands secrete sebum onto hair follicles.
- Hair grows from a follicle; the matrix at the bulb produces the hair. Nails grow from the nail matrix, and the nail plate is mainly compact keratin.
- First-degree burns affect the epidermis; second-degree burns involve the dermis and form blisters; third-degree burns destroy the full thickness and may be painless because nerve endings are damaged.
- Wound healing involves inflammation, clot formation, epithelial regeneration, granulation tissue and remodeling.
Worked example
A scald produces redness and blistering but the skin remains sensitive. Blistering indicates separation within the dermis or at the dermal-epidermal junction, so this is a partial-thickness or second-degree burn. A painless, leathery, white or charred area would suggest full-thickness destruction with nerve damage. The depth, not the surface area alone, determines whether healing can occur from epidermal appendages.
Traps that cost marks
Do not say the epidermis contains blood vessels. Do not confuse sebaceous glands with sweat glands; sebum is oily and associated with hair follicles. Do not claim third-degree burns are always painful. Remember that melanin is produced by melanocytes and transferred to keratinocytes; it is not the same as keratin.
Worked example
A superficial cut that bleeds little and heals without scarring mainly involves the epidermis and superficial dermis.