Which of the following is NOT a sensory receptor of the skin?

Correct Answer: B

Rationale: Sensory receptors in the skin detect stimuli like touch, pressure, or pain. Meissner corpuscles sense light touch, root hair plexuses detect hair movement, and nociceptors register pain all are receptors in the dermis or epidermis. Apocrine glands, however, are sweat glands associated with hair follicles, secreting sweat in response to stress or hormones, not sensing stimuli. They're part of the skin's excretory system, not its sensory network. This functional distinction excludes apocrine glands from being sensory receptors, aligning with their role in secretion rather than perception.

Correct Answer: C

Rationale: Skin produces vitamin D when exposed to UVB radiation, converting 7-dehydrocholesterol in the epidermis to previtamin D3, which becomes vitamin D3 (cholecalciferol). Calcium presence doesn't trigger this; it's a downstream effect of vitamin D. PTH signals the kidneys, not skin, to activate vitamin D later. The liver modifies the skin's product, adding a hydroxyl group, but doesn't initiate it. UV exposure is the critical first step, a photochemical reaction unique to skin, making this the correct condition.

Correct Answer: D

Rationale: Apocrine glands, a type of sudiferous gland, secrete a thicker, milky sweat into hair follicles, often in areas like the armpits, triggered by stress or hormones. 'Apocrin' is a nonsense term. Cerumin (cerumen) is earwax from ceruminous glands. Milk comes from mammary glands, not apocrine. As sweat glands, apocrine glands differ from eccrine by their secretion site and composition, contributing to body odor when broken down by bacteria, making sweat the accurate secretion.

Correct Answer: C

Rationale: Transdermal drugs are applied to the epidermis (e.g., via patches) and absorbed through the skin into the bloodstream for systemic effects, not limited to local action (topical). Muscle injection is intramuscular, and anal insertion is rectal, both unrelated. Application to the epidermis initiates the transdermal process, relying on diffusion through skin layers, a common delivery method in pharmacology, making this the precise definition.

Correct Answer: D

Rationale: Full-thickness burns over 20% cause life-threatening fluid loss (dehydration) by destroying the waterproof skin barrier and allow infection by removing protection against pathogens. Vitamin D loss isn't acutely fatal. Thermoregulation fails but is secondary to fluid and infection risks. Skin doesn't significantly excrete lactic acid, urea, or uric acid (kidney roles). The dual crisis of fluid loss and infection vulnerability drives burn mortality, as clinical management focuses on fluids and antibiotics, making this the critical pair.