* Hair Follicle: The hair follicle is the root of the hair. It's a small pocket in the skin that contains the hair root and various cell types responsible for hair growth.
* Hair Bulb: Located at the base of the hair follicle, the hair bulb is the living part of the hair. It contains:
* Dermal Papilla: A structure at the base of the hair bulb containing blood vessels that supply nutrients and oxygen needed for hair growth.
* Matrix: A layer of cells surrounding the dermal papilla that divide rapidly to create new hair cells. These cells are responsible for the hair's growth, color (through melanin production), and texture.
* Keratinization: As new cells are produced in the matrix, older cells are pushed upwards. These cells become filled with keratin, a tough protein that makes up the structure of the hair shaft. As they fill with keratin, they die and harden, forming the visible hair strand.
* Hair Growth Cycle: Hair growth isn't continuous. It follows a cycle with three main phases:
* Anagen (Growth Phase): This is the active growth phase, lasting several years for scalp hair. The cells in the hair bulb are rapidly dividing, and the hair shaft is lengthening. The duration of this phase determines the length of the hair.
* Catagen (Transition Phase): A short transition phase lasting a few weeks where hair growth slows down, and the hair follicle shrinks.
* Telogen (Resting Phase): The hair follicle is dormant for a few months, and the hair is not growing. Eventually, the old hair is pushed out as a new hair begins to grow in the anagen phase.
In summary: Hair growth comes from the rapid division of cells in the hair bulb, fueled by nutrients and oxygen from the blood supply. These cells produce keratin, which hardens and forms the hair shaft as they are pushed upwards. The entire process is regulated by the hair growth cycle and influenced by factors such as genetics, hormones, and nutrition.