Final answer:
The hair shaft is the visible part of the hair above the skin surface and is made of dead keratinized cells, while the hair root, located within the hair follicle, consists of living cells. The hair shaft consists of three layers: the cuticle, cortex, and medulla, and does not have any biochemical activity.
Step-by-step explanation:
Hair Structure and Growth
The hair shaft is the part of hair that is visible above the surface of the skin and consists of dead keratinocytes. These cells are filled with keratin, a type of protein that is also the main component of nails and skin. The visible portion of the hair, which is not anchored to the follicle, is made of tightly packed dead cells that have no biochemical activity and, therefore, are considered dead. This contrasts with the hair root, which is located within the hair follicle and consists of living cells. The hair root extends into the dermis and ends at the hair bulb, encompassing a layer of actively dividing basal cells known as the hair matrix.
The hair follicle is a tunnel-like segment of the epidermis that extends down into the dermis of the skin. Here, the hair bulb surrounds the hair papilla, which contains connective tissue, blood capillaries, and nerve endings. Furthermore, the hair shaft has three distinct layers: the cuticle (the outermost layer), the cortex (the middle layer), and at times, the medulla (the innermost layer).
Understanding the structure of hair, including the hair shaft, root, and associated components within the hair follicle, is essential in fields such as dermatology and trichology—the scientific study of the hair and scalp.