Structure, functions and phases of hair growth

Hair is very important for a person, and not only for biological, but also for cosmetic and aesthetic reasons, hair allows you to emphasize the image of a person, make it more attractive and attract the attention of the opposite sex. Many writers describe the beauty of women's hair and its magic. It's not for nothing that they say that a woman without beautiful hair is like a picture without a frame.

Hair covers almost the entire human body and performs the following functions:

  • protect the body from the harmful effects of the environment and mechanical influences;
  • participate in heat regulation (maintain the temperature balance of the body);
  • are organs of touch, as they are surrounded by the finest nerve endings.

The approximate chemical composition of healthy hair is as follows:

  1. 15% water,
  2. 6% lipids,
  3. 1% pigment,
  4. 78% protein.

Hair structure: outer and inner part

Each hair can be conditionally divided into 2 parts: the shaft (trunk) and the root. Kernel - This is the visible part of the hair that protrudes above the surface of the skin and grows from the hair follicles. The hair root is located in the skin layer and is surrounded by the root sheath. Together they are called hair follicle.

The hair shaft can be located at different angles relative to the surface in a wide range: from 10 to 90 degrees. A small angle of growth (~ 10-20 degrees) can sometimes create problems when creating a hairstyle, since it is difficult to style the hair in the opposite, unnatural direction for them. Also, with such a small angle of growth, it is possible for hair to grow into the skin, which causes inflammation.

The outer part of the hair has three layers:

  1. The core (inner part) contains non-keratinized cells.
  2. The cortex (cortex) makes up 90% of the hair mass. Consists of cells of an elongated shape. This is where melanin is found, which is responsible for hair color.
  3. The cuticle (outer layer) in structure resembles cone scales or shingles, where each subsequent part slightly coincides in area with the previous one.

Hair shaft structure

Other structures adjoin the hair follicle: the sebaceous gland, the sweat gland and the muscle that lifts the hair (thanks to which the expression “the hair stands on end” exists). In addition, the hair follicle is well vascularized. In men prone to baldness, the vascular apparatus of the hair follicle is hypersensitive to hormones (androgens): dihydrotestosterone and the enzyme 5-alpha reductase, which converts testosterone into dihydrotestosterone. During puberty, when the amount of androgens in the blood is increased, the vessels of the follicle persistently spasm, the nutrition of the hair follicle is disturbed, and, as a result, baldness occurs (even Hippocrates said that eunuchs do not go bald). It is important to note that only the hair of certain areas of the head has such an increased sensitivity to androgens, but not all hair on the human body.

Hair structure

The hair follicle is a receptacle for the hair root, which is also called the bulb. Bulb - This is a small thickening and consists of cells that are dividing intensively to form hair. The bulb has an unusual immune status, the violation of which is presumably one of the causes of alopecia areata.

In the lower part, adjacent to the bulb hair papillawhich contains blood vessels. The papilla is a very important part of the follicle, as it controls the condition and growth of the hair. If the papilla dies, the hair also dies. However, if for any reason the hair dies (for example, it is torn out by the roots), and the papilla is preserved, then a new hair will grow in its place.

Hair follicle Is a complex structure that is in constant cyclical development: the stages of anagen, catagen and telogen.

Hair growth stages

Anagen - the period of active hair growth.Lasts an average of 2-6 years. With age, the duration of the anagen phase decreases. The anagen growth phase is also divided into 6 stages:
The cells of the hair follicle increase in size, there is an intensive synthesis of RNA.
The hair follicle grows down into the epidermis and practically surrounds the dermal papilla. Cell differentiation begins into the various layers of the hair and the outer root sheath in the matrix ring that surrounds the dermal papilla.
Cell division continues. At this point, the hair follicle reaches its maximum length, which is 3 times longer than in the resting phase. The dermal papilla is also fully formed. Melanocytes (epidermal cells that are responsible for the production of melanin, which color the hair in a specific color) are located along the papilla cavity, each of which (each of the melanocytes) forms melanin granules. The outer shell of the follicle cavity is now an elongated cone that expands from above.
At this stage, melanocytes begin to produce melanin (pigment). Although the hair is already formed, it still does not extend beyond the cone-shaped cavity, which continues to expand.
The hair grows to the upper border of the epidermis, the bulb takes on a finished shape, which in some hairs is symmetrically rounded, in others it is compressed like an ellipse.
The last stage begins as soon as the hair begins to rise above the skin and continues until the catagen phase. In mice at the 6th stage of anagen, hair grows at a rate of 1 mm per day. In humans, this stage lasts from 2 years or more. Hair is produced at a rate of 0.5 mm per day.

Catagen - the period of transition from one stage to another. In the catagen stage, atrophy of the hair papilla begins, as a result of which the cells of the hair follicle, deprived of nutrition, stop dividing and undergo keratinization. This stage lasts only a few weeks, after which the short telogen stage begins, which smoothly passes into the developmental stage.

Telogen - a period of rest or rest of the hair. Interestingly, the mechanical removal of hair in the telogen stage always entails the onset of the anagen stage, that is, the hair begins to grow again. All hair that remains on the comb or falls out during the day is telogen hair.

Hair growth phases

Typically, in healthy people, approximately 80-90% of hair is in the anagen stage, 1-2% in the catagen stage, and 10-15% in the telogen stage. Studies show that profuse hair loss corresponds to a change in the above ratio: the percentage of hair in anagen and catagen decreases, but the percentage of telogen hair increases. If you notice that the amount of hair falling out during the day has increased dramatically, then know that this is the first sign of a deterioration in the condition of your head of hair. In people who are not prone to baldness, each new hair does not differ in thickness, potential length and other characteristics from the previous ones; at the same time, in balding hair, each new generation of hair decreases in thickness, color (brightens), the growth rate and duration of the anagen phase decrease. Ultimately, healthy hair gradually degrades to vellus and colorless hair.

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