Which of the following situations stimulates the skin to produce Vitamin D?

a. Secretes fluid to reduce friction between layers: This is correct. The pleural membranes secrete pleural fluid, which reduces friction between the visceral and parietal layers during breathing.

b. Secretes a substance that reduces surface tension of alveoli: This describes the function of surfactant, which is secreted by alveolar cells, not pleural membranes.

c. Secretes a substance to keep epithelial cells wet: This is a general description that doesn't specifically apply to pleural membranes.

d. Secretes fluid involved in protection from infections: While pleural fluid may have some protective roles, its primary function is to reduce friction, not directly to protect from infections.

a. Sebaceous: Sebaceous glands are located near hair follicles and produce sebum, an oily substance that lubricates the hair and skin, preventing dryness and keeping it supple.

b. Eccrine: Eccrine glands are sweat glands located throughout the skin and help regulate body temperature through sweating.

c. Ceruminous: Ceruminous glands are located in the ear canal and produce cerumen (earwax) which protects the inner ear from dust, debris, and insects.

d. Apocrine: Apocrine glands are sweat glands located in areas like the armpits and groin. They produce a thicker sweat that takes on an odor when broken down by bacteria.