Which of the following substances is not present in sweat?

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: B

Rationale: Melanocytes, located in the stratum basale, produce melanin, a pigment that absorbs UV radiation, protecting skin cells from DNA damage and reducing cancer risk. Darkening (tanning) enhances this shield. Keratinocytes make keratin, a structural protein, not pigment. Dendrocytes (likely dendritic cells) are immune-related, not pigment-producing. Merkel cells detect touch, not UV protection. Melanin's role in UV defense, distributed to surrounding keratinocytes, is a well-established skin adaptation, making melanocytes the correct cell type.

Correct Answer: A

Rationale: The integumentary system officially includes the epidermis and dermis. The epidermis is the outer protective layer, while the dermis beneath it contains connective tissue, glands, and nerves. The hypodermis, though adjacent, is the subcutaneous layer, not part of the integument proper. Listing epidermal sublayers (germinativum to corneum) excludes the dermis, incomplete for the integument. Combining the corneum with dermal layers omits other epidermal parts. Standard anatomy defines the integument as epidermis and dermis, aligning with their integrated protective roles.

Correct Answer: A

Rationale: Sebaceous glands are the skin's oil glands, secreting sebum into hair follicles to lubricate skin and hair, distinct from sweat glands. Eccrine (merocrine) glands secrete watery sweat to the surface. Apocrine glands secrete sweat into follicles. The term 'sebaceous' directly refers to oil production, a role not shared by the others, all of which are sudiferous glands. This specificity in skin histology identifies sebaceous glands as the oil producers, making them the correct synonym.

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.