What is the fibrous protein in our skin that protects it from abrasion?

Correct Answer: B

Rationale: Keratin, a fibrous protein in the epidermis, fills the stratum corneum's dead cells, protecting against abrasion by forming a hard, renewable barrier. Melanin is a pigment for UV protection, not abrasion. Sebum is an oily secretion, not fibrous. Elastin, in the dermis, provides elasticity, not abrasion resistance. Keratin's toughness, shed and replaced as skin wears, is the key anti-abrasion mechanism, widely recognized in skin structure.

Correct Answer: D

Rationale: Arrector pili muscles, small smooth muscles in the dermis attached to hair follicles, contract under sympathetic nervous stimulation (e.g., cold or fear), pulling hairs upright and causing goosebumps (piloerection). They don't sense temperature thermoreceptors do that. Melanin is from melanocytes, not muscles. 'Ejecting hair shafts' isn't a function; hairs grow or shed via follicles, not muscle action. Goosebumps, an evolutionary remnant to trap air or signal emotion, define their primary role, per skin anatomy.

Correct Answer: B

Rationale: The subcutaneous tissue, or hypodermis, primarily contains adipose tissue, fat cells that insulate and store energy, cushioning underlying structures. Blood vessels and sweat glands are mostly in the dermis, though some vessels traverse the hypodermis. Collagen fibers dominate the dermis, not the hypodermis, which has looser connective tissue. Melanocytes are epidermal, not subcutaneous. Adipose tissue's prevalence defines the hypodermis's role, distinguishing it from skin layers above, making this the correct content.

Correct Answer: A

Rationale: Merkel cells, in the stratum basale, connect to nerve endings (Merkel discs) to detect sustained pressure and touch, providing fine tactile discrimination. Temperature is sensed by thermoreceptors, pain by nociceptors, and itch by specific receptors, none primarily Merkel-related. Their role in continuous pressure sensation, critical for texture perception, distinguishes them in the skin's sensory array, making this the correct sensation.

Correct Answer: C

Rationale: Lubrication and protection involve sebum production by sebaceous glands, moisturizing skin and hair while adding a protective layer against microbes and dryness. Thermoregulation uses sweat, sensation involves receptors, and vitamin D synthesis uses UV, none tied to oil. Sebum's role in maintaining skin integrity and suppleness defines this function, making it the correct answer.