What is the largest organ in the human body?

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: 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.

Correct Answer: D

Rationale: The hypodermis insulates via adipose tissue, reducing heat loss, and stores energy as fat reserves, supporting survival during scarcity. Sweat production and temperature regulation (via vessels) occur in the dermis. The physical barrier is the epidermis's role. Insulation and energy storage define the hypodermis's primary function, cushioning and sustaining the body, making this the correct answer.