Biological Systems MCAT Practice Exam 2025 – Complete Study Resource

Hair follicles produce hair primarily in the form of keratinized cells. As hair follicles grow, they generate living epithelial cells within the hair bulb, but these cells undergo a process of keratinization as they move upward through the follicle. During this process, the cells synthesize keratin, a fibrous protein that is integral to the structure of hair. As the cells keratinize, they lose their nuclei and become dead cells, which form the hair shaft that is visible above the skin.

Therefore, the process of hair production truly highlights the transition from living to dead cells during hair maturation, emphasizing that the final product is indeed composed of keratinized cells. This process is critical in understanding hair structure and function, as keratin provides both strength and resilience to hair, enabling it to withstand daily wear and tear.

While living epithelial cells are involved in the initial formation of the hair and contribute to its growth, the hair that emerges from the follicle is not living, but rather a composition of dead, keratin-rich cells. Hence, the focus on keratinized cells captures the essence of what hair truly is when it emerges from the follicle.