Which of the following is not a major component of a hair shaft?
Cuticle Cortex
External root sheath
Medulla
Keratin
The correct answer and explanation is:
The correct answer is External root sheath.
A hair shaft is made up of several layers and components, each playing a critical role in its structure and function. The major components of a hair shaft include the cuticle, cortex, medulla, and keratin. Here’s a breakdown of each component:
- Cuticle: This is the outermost layer of the hair shaft, consisting of overlapping scale-like cells that help protect the inner layers of the hair. The cuticle is essential for the hair’s strength and resilience, as well as contributing to its shine and smoothness.
- Cortex: Beneath the cuticle, the cortex makes up the bulk of the hair shaft. It is composed of keratin fibers and gives the hair its strength, elasticity, and texture. The cortex also contains melanin, which gives hair its color. The amount and type of melanin determine whether hair is dark or light.
- Medulla: The medulla is the innermost layer of the hair shaft and is not always present in all hair types. It is a soft, spongy core that is less dense than the cortex. In thicker or coarser hair, the medulla is usually more pronounced, while it may be absent or fragmented in finer hair.
- Keratin: Keratin is a fibrous protein that makes up the cuticle, cortex, and medulla. It is responsible for the strength and durability of hair. Keratin is produced in the hair follicle, and as the hair grows, it hardens, forming the solid structure of the hair shaft.
On the other hand, the external root sheath is not part of the hair shaft. It is a part of the hair follicle, which is the structure from which hair grows. The external root sheath surrounds the hair bulb and helps in the growth and development of the hair shaft, but it does not contribute to the hair’s composition once it emerges from the scalp.
In summary, the external root sheath is involved in the development of the hair but does not form part of the actual hair shaft structure.