On which part of the integument is most of the body's normal flora located?

Correct Answer: B

Rationale: Normal flora (bacteria) reside on the epidermis, particularly the stratum corneum, the skin's surface exposed to the environment. The dermis, beneath, is internal and sterile unless breached. 'Microdermis' isn't a term; likely a typo. The hypodermis, deeper still, isn't a flora habitat. The epidermis, as the outermost layer, hosts these microbes, which thrive without penetrating living tissue, making it the correct location.

Correct Answer: B

Rationale: The stratum corneum, the epidermis's outermost layer, is a barrier of dead, keratinized cells and lipids that prevents pathogen entry and water loss, protecting the body from infection and dehydration. Sensation involves dermal receptors, not this dead layer. Melanin is produced in the stratum basale, not corneum. Temperature regulation uses sweat and vessels, not this passive shield. Its tough, waterproof structure, constantly shedding to renew protection, defines its primary role, a cornerstone of skin defense.

Correct Answer: C

Rationale: Sebum, an oily secretion from sebaceous glands, lubricates skin and hair, preventing dryness and brittleness while adding a minor protective layer. UV protection is melanin's role, not sebum's. Temperature regulation involves sweat and vessels, not oil. Melanin production is melanocytes' task, not glands'. Sebum's lipid content, delivered via hair follicles, maintains skin suppleness and waterproofing, making lubrication its primary function, per skin physiology.

Correct Answer: B

Rationale: Melanin, produced by melanocytes, protects against UV radiation by absorbing it, preventing DNA damage and reducing skin cancer risk, darkening as a shield (tanning). Melatonin regulates sleep, not UV defense. Sebum lubricates, not protects from UV. Collagen provides structure, not photoprotection. Melanin's UV-absorbing property, distributed in the epidermis, is the skin's primary anti-radiation mechanism, making it the correct answer.

Correct Answer: A

Rationale: Ruffini endings, in the dermis, detect sustained pressure and skin stretch, contributing to proprioception and grip stability, often responding to vibration too. Light touch and texture are Meissner's corpuscles' role, temperature changes are thermoreceptors', and sweat production is glandular. Their mechanoreceptive function for deep pressure distinguishes them, making this their primary role.