If a drug is administered 'transdermally', which of the following applies?

Correct Answer: C

Rationale: Transdermal administration means a drug is absorbed through the skin into the bloodstream for systemic effects (e.g., nicotine patches), not just local action (topical). Injection into the dermis is intradermal, and into subcutaneous fat is hypodermic, both distinct from surface application. 'Trans' indicates crossing the skin barrier, requiring penetration of the stratum corneum to reach circulation, a method reliant on skin permeability, making systemic action the defining feature.

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: The skin is the largest organ in the human body, covering an average surface area of about 1.5 to 2 square meters in adults and weighing approximately 4-5 kilograms, including the epidermis, dermis, and hypodermis. It surpasses the heart, liver, and lungs in both size and mass when considered as a whole organ system. The heart, though vital, is a small muscular organ, roughly 300 grams. The liver, at about 1.5 kilograms, is significant but smaller in surface area. The lungs, while expansive internally, have a combined weight of around 1 kilogram and less external coverage than skin. The skin's extensive role in protection, sensation, and thermoregulation, coupled with its sheer physical extent across the body, confirms it as the largest organ, a fact well-established in anatomy.

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.