What is the structure at the end of the hair follicle called?

The correct answer is the hair bulb. The hair bulb is the rounded structure at the base of the hair follicle. It is where hair growth begins and is responsible for the production of hair. Within the bulb, the hair cells are supplied with nutrients from blood vessels located in the papilla, which is a structure at the bottom of the bulb that contains connective tissue and is essential for hair development.

The hair bulb is vital because it is where the keratinocytes proliferate and differentiate to form the hair shaft. The bulb's composition is crucial as it houses the stem cells that contribute to hair growth. As such, understanding the role and function of the hair bulb is fundamental in cosmetology, especially when discussing hair health and growth cycles.