Sebaceous glands

Correct Answer: B

Rationale: Sebaceous glands are oil-producing glands typically associated with hair follicles, secreting sebum to lubricate hair and skin. They are not sweat glands, which produce sweat (eccrine and apocrine glands have different roles). They don't function in response to touch; that's more relevant to sensory receptors like Merkel cells. Nor do they release a watery solution of salt and waste that describes eccrine sweat glands. Their anatomical and functional link to hair follicles, where they empty sebum into the follicle, is a classic feature of skin histology, making this the correct association.

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.

Correct Answer: D

Rationale: Keratin is the fibrous protein that fills the dead cells of the stratum corneum, the outermost epidermal layer, providing toughness and resistance to abrasion. Granstein and dermin are not recognized proteins in skin anatomy likely distractors. Melanin, produced by melanocytes deeper in the epidermis, is a pigment for UV protection, not a structural filler in dead cells. Keratin, produced by keratinocytes as they move upward and die, hardens the corneum, forming a protective barrier, a process well-documented in histology as essential to skin's durability and waterproofing.