The thickest portion of skin in man is found at the region of

Correct Answer: D

Rationale: The correct answer is D: Sole. The thickest portion of skin in humans is found on the soles of the feet due to the constant pressure and friction they endure from walking and standing. This leads to a thicker layer of protective skin to provide support and cushioning. The head (A), thumb (B), and palm (C) do not experience the same level of pressure and friction as the soles, resulting in thinner skin layers in those areas. Thus, the sole is the correct choice for the thickest portion of skin in humans.

Correct Answer: D

Rationale: The correct answer is D: Shrew. Shrews are known to have red-colored sweat due to a pigment called porphyrin. This pigment gives their sweat a reddish hue. Kangaroos, elephants, and rhinoceroses do not have red sweat. Kangaroos sweat is colorless, elephants' sweat is clear, and rhinoceroses sweat may appear red due to mud or dust, not because of any pigment. Therefore, the red-colored sweat is unique to shrews, making choice D the correct answer.

Correct Answer: D

Rationale: The correct answer is D: Cortex. Melanin pigment granules are found in the cortex layer of the hair shaft. This is where the color of the hair is determined. The cortex contains the majority of the hair's melanin, which gives hair its natural color. The other choices, A: Hair follicle, B: Hair papilla, and C: Medulla, do not contain melanin pigment granules. The hair follicle is the root of the hair, the hair papilla is a structure at the base of the follicle, and the medulla is the innermost layer of the hair shaft that may or may not contain pigment depending on the hair color.

Correct Answer: B

Rationale: The correct answer is B: Elasticity of dermis decreases. As people age, the dermis layer of the skin loses collagen and elastin fibers, leading to a decrease in skin elasticity, resulting in loose and wrinkled skin. The other choices are incorrect because A (Stratum germinativum becoming more active) would actually lead to increased cell turnover and potentially smoother skin, C (Stratum corneum becoming thicker) would result in thicker skin but not necessarily loose and wrinkled, and D (poor blood supply to the skin) would affect overall skin health but not directly cause loose and wrinkled skin.

Correct Answer: B

Rationale: The correct answer is B: Involuntary. Muscles found in the skin, such as arrector pili muscles responsible for hair erection, are involuntary muscles. These muscles respond to autonomic nervous system signals without conscious control. Choice A is incorrect because muscles in the skin are not under voluntary control. Choice C is incorrect because it suggests a combination of voluntary and involuntary muscles, which is not accurate for skin muscles. Choice D is incorrect as there are indeed involuntary muscles in the skin.