Which of the following hair structures serves as a storage for stem cells?

• A. Inner root sheath
• B. Outer root sheath
• C. Hair bulb
• D. Dermal papilla

Answer: (B)

The outer root sheath is a critical structure associated with hair follicles, serving not only as a protective layer for the hair shaft but also as an important reservoir for stem cells. These stem cells are essential for the growth and regeneration of hair. The outer root sheath contains progenitor cells that can differentiate into various cell types necessary for hair development and follicle health.

In particular, during the hair follicle's growth phase, or anagen phase, cells in the outer root sheath can proliferate and contribute to the formation of new hair strands. This ability to store and facilitate the activation of stem cells is why the outer root sheath plays such a pivotal role in hair growth cycles.

Other structures, like the inner root sheath or hair bulb, while essential to the structure and function of hair follicles, do not primarily serve as storage for stem cells. The hair bulb is more focused on providing nourishment and supporting the hair growth process rather than acting as a reservoir for stem cells. Similarly, the dermal papilla, found at the base of the hair follicle, is crucial for signaling growth and development but is not primarily a storage site for stem cells.