Exposure to ultraviolet light (sunlight) causes the skin to darken by increasing the production of

Correct Answer: D

Rationale: The correct answer is D: Melanin. Melanin is a pigment produced by skin cells in response to UV exposure, acting as a natural defense mechanism to protect the skin from sun damage. Collagen (A) is responsible for skin firmness, not skin darkening. Carotene (B) is a pigment found in certain foods like carrots but does not directly contribute to skin darkening. Keratin (C) is a protein that provides structure to the skin, hair, and nails, but it does not play a role in skin darkening. Therefore, the production of melanin is specifically increased in response to UV light exposure, making it the correct choice.

Correct Answer: A

Rationale: Step 1: Cyanosis is a bluish discoloration of the skin due to insufficient oxygen in the blood. Step 2: Oxygen-starved blood appears bluish as it reflects less red light. Step 3: Therefore, cyanosis signifies a lack of oxygen in the blood, not related to sun exposure. Summary: Choice A is correct as it accurately reflects the physiological cause of cyanosis. Choices B, C, and D are incorrect as they do not relate to the underlying mechanism of cyanosis.

Correct Answer: D

Rationale: The correct answer is D, all of the choices. UV radiation damages collagen and elastin fibers, leading to skin wrinkling. Aging causes a decrease in collagen production and skin elasticity, contributing to sagging. Hormonal changes, like decreased estrogen levels, also impact collagen production and skin thickness. Therefore, all three factors (UV radiation, aging, hormonal changes) play significant roles in causing skin wrinkle and sagging. Other choices are incorrect as they do not encompass the comprehensive factors that contribute to these skin conditions.

Correct Answer: D

Rationale: The correct answer is D, stratum corneum. Insensible perspiration involves the constant evaporation of water through the skin to maintain body temperature. The stratum corneum is the outermost layer of the epidermis, consisting of dead cells that are continuously shed and replaced. This layer provides a barrier function and regulates the loss of water from the body. The other choices (A: stratum granulosum, B: stratum basale, C: stratum spinosum) are not involved in insensible perspiration as they are deeper layers of the epidermis responsible for cell division, keratin production, and structural support.

Correct Answer: C

Rationale: The correct answer is C: Vellus hairs. Vellus hairs are fine, unpigmented hairs that cover most of the body surface. They are short, thin, and barely noticeable. Velvet hairs (A) and follicular hairs (B) are not specific types of hairs. Terminal hairs (D) are thicker, coarser, and darker hairs found on the scalp, armpits, and pubic region, not fine and lacking pigment like vellus hairs. Therefore, vellus hairs are the correct choice for fine, pigmentless hairs covering much of the body surface.