The papillary layer of the dermis is most closely associated with which layer of the epidermis?

Correct Answer: D

Rationale: The papillary layer of the dermis is the uppermost layer of the dermis, characterized by loose connective tissue and finger-like projections (papillae) that interlock with the deepest layer of the epidermis, the stratum basale. The stratum basale, also called the basal layer, is where new skin cells are produced and it rests directly on the papillary dermis, forming a strong connection via the basement membrane. The stratum spinosum lies above the basale and is thicker, with spiny cells, but it's not in direct contact with the papillary layer. The stratum granulosum is higher up, involved in keratinization, and the stratum corneum is the outermost dead layer, far from the dermis. The anatomical proximity and functional relationship between the papillary layer and stratum basale, including nutrient exchange and anchoring, make it the most closely associated layer.

Correct Answer: C

Rationale: Bedsores (pressure ulcers) develop from prolonged pressure on skin, cutting off blood flow and causing tissue damage, often in bedridden patients. They're preventable by eliminating pressure points through repositioning, cushions, or mattresses, relieving compression on vulnerable areas like the heels or sacrum. Topical moisturizers may help skin health but don't treat established sores. Deep massages could worsen damage, not cause it. Dry skin isn't the cause; ischemia from pressure is. Prevention via pressure relief is a standard clinical approach, making this the correct answer.

Correct Answer: B

Rationale: Goosebumps occur when small muscles attached to hair follicles contract, causing hairs to stand upright and skin to pucker. These are the arrector pili muscles, smooth muscles in the dermis anchored to the hair follicle base and the epidermal-dermal junction. When stimulated by cold or emotion (via the sympathetic nervous system), they contract, pulling hairs erect, an evolutionary vestige from furrier ancestors to trap heat or signal threat. Sebaceous glands secrete sebum to lubricate hair and skin, not to cause goosebumps. 'Cappilary' (likely a typo for capillary) refers to blood vessels, which adjust for temperature but don't directly produce goosebumps. Collagen provides dermal strength but is a passive fiber, not a muscle. The arrector pili's action is involuntary, linked to thermoregulation and emotional response, and its distinct role in piloerection visible as goosebumps sets it apart as the key structure in this phenomenon.

Correct Answer: B

Rationale: Hair color arises from melanin, a pigment produced by melanocytes. Located in the hair follicle's bulb, melanocytes synthesize eumelanin (brown/black) or pheomelanin (red/yellow), injecting it into surrounding keratinocytes, which form the hair shaft's keratin structure. The amount and type of melanin determine color more eumelanin darkens hair, while pheomelanin lightens it. Keratinocytes, the majority cells in hair and epidermis, build the hair but don't produce pigment; they receive it from melanocytes. Langerhans cells are immune cells in the epidermis, unrelated to pigmentation. Merkel cells, at the epidermal-dermal junction, sense touch, not color. Melanocytes' role in hair, skin, and eye pigmentation is genetically regulated, with activity declining in graying hair. Histological studies of follicles confirm melanocytes as the pigment source, distinguishing them from structural or sensory cells in hair development.

Correct Answer: B

Rationale: Sweat, from eccrine glands, contains water (99%), urea, lactic acid, and salts like sodium chloride, but not calcium in significant amounts. Water is the primary component, cooling the body via evaporation. Urea, a metabolic waste, is excreted in trace amounts, reflecting sweat's minor excretory role. Lactic acid, from muscle activity, appears during exertion, lowering sweat pH. Sodium, potassium, and chloride ions maintain electrolyte balance, but calcium, critical in blood and bone, is conserved by the kidneys, not sweat glands. Analysis of sweat composition shows negligible calcium unlike urine, where it's excreted. This reflects sweat's focus on thermoregulation and minor waste removal, not mineral loss. Physiological studies confirm calcium's absence as a standard component, distinguishing it from other substances routinely detected in sweat.