Which glands secrete 'oil' into a hair follicle?

Correct Answer: D

Rationale: Sebaceous glands secrete sebum, an oily substance, into hair follicles to lubricate hair and skin, found in the dermis. Apocrine glands secrete sweat into hair follicles, not oil. Eccrine glands secrete watery sweat directly to the skin surface via ducts. Ceruminous glands produce cerumen (earwax), not oil for hair follicles. Sebaceous glands' association with follicles and their oily output distinguish them in skin physiology, making them the correct gland type for this function.

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: A

Rationale: Melanocytes in the stratum basale produce melanin, the pigment that darkens skin (tanning) upon sunlight exposure, absorbing UV to protect cell nuclei. Keratinocytes form keratin, not pigment, though they receive melanin. Dendrocytes (likely dendritic cells) handle immunity, not tanning. Lymphocytes, immune cells, aren't skin-based or pigment-related. Melanocytes' UV-responsive melanin production is the mechanism behind tanning, a protective adaptation, making them the correct cell type.

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.