What is the sheath that surrounds the hair called?

The correct choice identifies the structure known as the hair follicle, which is crucial for hair growth and development. The hair follicle is a dynamic organ located in the dermis layer of the skin. It surrounds the hair root, anchoring the hair into the scalp or skin, and plays a vital role in the hair's lifecycle. The follicle is responsible for producing hair and contains important cells and structures that nourish and support hair growth.

In the context of hair physiology, the hair shaft refers to the visible part of the hair that extends above the skin, while the hair root is the portion located below the skin's surface, housed within the hair follicle. The hair bulb is found at the base of the hair follicle and is where hair cells proliferate and keratinize to form hair strands. However, it is the hair follicle that specifically refers to the whole sheath encasing and supporting the root, making it the correct answer.