Anagen phase

Hair!

The hair consists of a shaftand a root. The shaft is located on the surface of the skin and the root is immersed in the skin.

The shaft has three layers: the medulla, the cortex and the cuticle.

The hair root consists of epithelial cells that are at different stages of the formation of the cortex, medulla and cuticle.
The hair root ends with an extension - the hair follicle, It consists of epithelial cells that divide. Reproducing, the cells of the hair follicle move to the medulla, cortex of the hair root and its cuticle. This is how the hair grows!
From below, the connective tissue of the dermis with capillaries protrudes into the hair follicle (this is the hair papilla, it provides nutrition to the hair).
The hair follicle is surrounded by two epithelial sheaths (external and internal).

The internal epithelial hair root sheath is a derivative of the hair follicle. It consists of three layers: the cuticle, Huxley's inner layer, Henle's outer layer.

The outer epithelial hair root sheath is formed by the basal and spinosum layers of the epidermis. The hair follicle is surrounded on the outside by the connective tissue of the dermis - this is a hair bag!

The hair cuticle - the outermost layer of the hair, consists of horny scales that overlap each other in the form of tiles; These scales contain hard keratin and have no melanin pigment!
Cortex- makes up the bulk of the hair. Here the processes of keratinization are very intensive. It consists of flat horny scales with hard keratin, pigment inside.
Medulla is found in long and bristly hair. It consists of polygonal epithelial cells that lie on top of each other in the form of coin columns. There are processes of keratinization, but not actively, so cells can have nuclei or their remnants. It contains pigment, but with age, its amount decreases and the hair turns gray.

Hair grows in cycles of various phases:

anagen is the growth phase;
catagen is the involuting or regressing phase;
telogen, the resting or quiescent phase

(names derived using the Greek prefixes ana-, kata-, and telos- meaning up, down, and end respectively).

Each phase has several morphologically and histologically distinguishable sub-phases. Prior to the start of cycling is a phase of follicular morphogenesis (formation of the follicle). There is also a shedding phase, or exogen, that is independent of anagen and telogen in which one or several hairs that might arise from a single follicle exits. Normally up to 90% of the hair follicles are in anagen phase, while 10–14% are in telogen and 1–2% in catagen. The cycle's length varies on different parts of the body. For eyebrows, the cycle is completed in around 4 months, while it takes the scalp 3–4 years to finish; this is the reason eyebrow hair have a much shorter length limit compared to hair on the head. Growth cycles are controlled by a chemical signal like epidermal growth factor. DLX3 is a crucial regulator of hair follicle differentiation and cycling.

Anagen phase

Anagen is the active growth phase of hair folliclesduring which the root of the hair is dividing rapidly, adding to the hair shaft. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2–7 years; this period is genetically determined. At the end of the anagen phase an unknown signal causes the follicle to go into the catagen phase.

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