What is the primary function of the stratum corneum in the epidermis?

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: 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.

Correct Answer: C

Rationale: Meibomian glands, in the eyelids (part of the integumentary system), secrete an oily substance into tear film, lubricating the eyes to prevent evaporation and dryness. Temperature regulation involves sweat glands, tears come from lacrimal glands (not integumentary), and sweat is from sudiferous glands. Their role in eye lubrication, maintaining tear stability, makes this their primary function.