Hair Structure And Hair Growth Cycle

Hair is a simple structure that is made up of Protein filaments called Keratin which is also the primary component of finger and toe nails. Hair acts as a barrier to foreign particles. It's an important part of appearance and creates gender identity. Hair is the only body structure that can completely renew itself without scarring. Humans develop hair follicles during fetal development, and no new follicles are produced after birth. Hair color is mostly the result of pigments, which are chemical compounds that reflect certain wavelengths of visible light.

Hair shape (round or oval) and texture (curly or straight) is influenced heavily by genes. The physical appearance of hair can be affected by nutritional status and intentional alteration (heat curling, perms, straightening, etc.)

Hair diagram

Hair Structure: Hair is made up of two separate structures
The hair follicle: which exists below the skin.
The hair shaft: which is the hair that we see.

The HAIR FOLLICLE is the living part of the hair. It contains the germinal matrix, which is where cells produce new hairs. It contains the bulb, which is the stocking-like structure that surrounds the papilla and germinal matrix. It's fed by capillaries. The follicle is surrounded by an inner and outer sheath that protects and molds the growing hair shaft. The inner sheath follows the hair shaft and ends just before the opening of the sebaceous gland. The outer sheath continues all the way up to the sebaceous gland.

The HAIR SHAFT it the dead hair we can actually see. The innermost layer: This is called the medulla. Depending on the type of hair, the medulla isn't always present. The middle layer: This is called the cortex, which makes up the majority of the hair shaft. Both the medulla and the cortex contain pigmenting cells that are responsible for giving hair color. The outermost layer: This is called the cuticle, which is formed by tightly packed scales in an overlapping structure that resemble roof shingles. Many hair conditioning products are formulated to even out the cuticle by smoothing out its structure.

The Growth Cycle The anagen phase is the active or growth phase of the hair. Most hair is constantly growing and spends three to four years in this stage. Hair grows around half an inch a month, and faster in the summer than in winter. In the growth phase, or anagen phase, a full-length hair averages 18 to 30 inches. The anagen phase is generally longer in Asians, and can last as much as 7 years with hair being able to grow to 1 meter. The span at which the hair remains in this stage of growth is determined by genetics. The longer the hair stays in the anagen phase, the longer it will grow. During this phase, cells neighboring the papilla in a germinative layer divide to produce new hair fibers and the follicle buries itself into the dermal layer of the skin to nourish the strand. About 85%–90% of the hairs on one's head are in the anagen phase at any given time.

The catagen phase is a transitional stage, and 3% of all hairs are in this phase at any given time. It lasts for two to three weeks. It allows the follicle to renew itself. During this time, the hair follicle shrinks due to disintegration and the papilla detaches and "rests," cutting the hair strand off from its nourishing blood supply. Signals sent out by the body determine when the anagen phase ends and the catagen phase begins. The telogen phase is the resting phase, which lasts for about three months and accounts for 10% to 15% of all hair. During the telogen, the follicle remains dormant for one to four months. In this phase, the epidermal cells lining the follicle channel continue to grow as normal and may accumulate around the base of the hair, temporarily anchoring it in place and preserving the hair for its natural purpose without taxing the body's resources needed during the growth phase.

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