Which part of the hair structure includes the cuticle, cortex, and medulla?

The hair shaft is the part of the hair structure that includes the cuticle, cortex, and medulla. The cuticle is the outermost layer, consisting of overlapping scale-like cells that protect the inner layers from damage and environmental hazards. Below the cuticle is the cortex, which makes up the majority of the hair's structure and contains fibrous proteins and melanin, contributing to the hair's strength, color, and texture. The innermost layer is the medulla, which is often absent in finer hair types but can provide additional structural support in thicker strands.

In contrast, the hair follicle is the structure located beneath the surface of the skin that encases the hair root and is responsible for hair growth. The hair root is the portion of the hair that is embedded in the follicle, while the hair bulb is located at the base of the hair follicle and contains the hair matrix, where cell division occurs to produce new hair. Therefore, these other choices refer to different components of the hair growth system rather than the specific parts of the hair structure itself.