The hypodermis is which of the following?

Correct Answer: C

Rationale: The hypodermis, or superficial fascia, is the subcutaneous layer of fat and connective tissue beneath the dermis, not part of the integument (epidermis and dermis). It's not the outer layer (epidermis) or inner layer of the skin proper (dermis is deeper within the integument). It is vascularized, with blood vessels supplying it, not reliant solely on diffusion like the epidermis. Its exclusion from the integument and role as a cushion and insulator define it anatomically, making this the correct characterization.

Correct Answer: B

Rationale: The integument comprises the epidermis and dermis, with the dermis as the deeper layer, including the papillary and reticular sublayers. The epidermis is superficial, with the stratum corneum as its topmost part. The papillary dermal layer is the upper dermis, not the deepest. The dermis, extending beneath the epidermis to the hypodermis boundary, is the integument's deepest component, housing glands and connective tissue, making it the correct answer.

Correct Answer: C

Rationale: Melanin, produced by melanocytes in the stratum basale, is the pigment responsible for skin color, ranging from light to dark tones, and absorbs UV radiation to protect underlying cells from DNA damage. Melatonin, a hormone from the pineal gland, regulates sleep, not skin color. Hemoglobin, in red blood cells, gives a pinkish hue via dermal blood vessels but isn't a skin pigment or UV shield. Collagen, a dermal protein, provides structure, not pigmentation or UV protection. Melanin's dual role in coloration and photoprotection, darkening with UV exposure (tanning), makes it the correct pigment, per dermatological understanding.

Correct Answer: A

Rationale: The epidermis grows hair and nails via specialized structures: hair from follicles' matrix cells in the epidermal root, and nails from the nail matrix, both derived from epidermal keratinocytes. The dermis supports follicles with connective tissue and vessels but doesn't grow them. The hypodermis (subcutaneous tissue) provides fat and anchoring, not growth. The epidermis's role in generating these keratinized appendages, through cell division in basal layers, makes it the correct layer, per integumentary development.

Correct Answer: C

Rationale: The integumentary system's primary function is protection, shielding the body from pathogens, UV radiation, and physical damage via the skin, hair, and nails. Nutrient storage occurs in the hypodermis, a secondary role. Sensation, via receptors, is important but not primary. Gas exchange is the respiratory system's job, not skin's. Protection, encompassing barriers like the stratum corneum and immune responses, defines the system's core purpose, making it the correct answer.