We are having more portion of hair on scalp than the body parts like legs, arms, underarms, thighs, chests, mustache, beard, eyebrows and eyelashes and the texture and length of scalp hair also differs from the body hair. To understand the texture and growth of human hair let us have look on the anatomy of hair.
Hair Anatomy
Human hairs come out from the hair follicles which rest within the fatty layer of the human scalp. We believe that hair grows as the single strands but it is just a misconception as the human hair grows in the natural grouping of 1-4 hairs per grafts.
The topmost part of the hair is the strands which can be seen over the scalp and these strands come out from the hair follicles that have an individual base called hair bulb. The entire growth of hair occurs in the bulb and even the nourishment of hair also happen throws the hair bulb from the blood vessels within the dermis. The hair cells separate and develop to produce the hair shaft and the most surprising fact about the hair is that the hair develops and remain in the soft form under the epidermis but it gets hardens when coming out from the scalp.
What are the parts of human hair?
There are five main parts of the hair that can be defined as follows
- The dermal papilla is the part which is responsible for hair cycle and the growth. it is comprised of androgen receptors which make it sensitive for the presence of DHT
- Matrix is the part that surrounds the dermal papillae. The matrix contains all cells that are needed for the growth of hair and for the development of hair parts. Matrix and dermal papillae are called as hair bulb in the combined form.
- Outer root sheath is the third most important and outer part of the hair. This part covers the hair follicles inside the dermis and transit through the epidermis.
- The fourth important part of the hair is the inner root sheath which comprised of further three parts such as Henley layer, Huxley layer, and cuticle. The parts of this inner root sheath are responsible for the stabilization of hair means it secures the hair from loss and let them grow with strength.
- The hair shaft is the fifth important part and it is made up of three layers named as medulla, cortex, and cuticle.
Hair growth cycle
Hair is made up of the protein called keratin and during its lifespan hair passes through the three phases of the hair cycle as follows
- Anagen is the growth phase of the hair cycle. In this phase, most of the growth of hair occurs at a given time period which can be of several years
- Catagen is the transitional phase in which hair follicles get shrink and the hair growth slows down. This phase remain for a few weeks
- Telogen phase is the phase that remains for a few months and during this phase, hair get detached from follicles and new hair take the position of older hair and enter into the growth phase