folículo

A folículo is a biological structure that produces hair. These structures are found in the skin of mammals. A hair follicle is a small, sac-like invagination of the epidermis that envelops the root of a hair. The follicle is responsible for the growth and cycling of the hair shaft.

The development of a hair follicle begins during fetal development. A downgrowth of epidermal cells penetrates the underlying dermis, forming a cord that will eventually become the follicle. At the base of this cord, a dermal papilla, a small cluster of connective tissue, invaginates. This papilla is crucial for hair growth as it contains blood vessels that supply nutrients to the growing hair.

The hair follicle is composed of several layers. The outer root sheath is a continuation of the epidermis, while the inner root sheath is a specialized structure that surrounds and supports the developing hair shaft. The hair shaft itself is made of keratin, a tough protein.

Hair follicles go through cycles of growth. The anagen phase is the active growth period, during which the hair shaft elongates. This is followed by the catagen phase, a transitional period where growth stops and the follicle begins to shrink. Finally, the telogen phase is the resting period, after which the old hair is shed and a new one begins to grow from the same follicle. The length of these phases varies depending on the location of the follicle on the body and individual factors. Diseases and conditions can affect the normal functioning of hair follicles, leading to hair loss or changes in hair texture.