Follikels

Follikels are small sac-like structures that appear in various tissues. In general, a follikel is a cavity lined by epithelium that surrounds or contains cells or fluids essential to tissue function or development.

In the skin, hair follikels are tubular invaginations of the epidermis that produce and anchor hair shafts. Each follikel houses a hair bulb, hair matrix cells, and often a sebaceous gland whose secretions lubricate the hair. Hair follikels undergo cyclical phases—anagen (growth), catagen (regression), and telogen (rest)—which determine hair growth and shedding. Disorders of hair follikels include folliculitis and other follicle-related conditions.

In the ovaries, ovarian follikels are functional units that enclose an oocyte and surrounding somatic cells. They progress from primordial to primary, secondary (pre-antral), and antral follicles, culminating in a preovulatory (Graafian) follikel. Ovulation releases the oocyte and transforms the remainder into the corpus luteum. Follicle-stimulating hormone and luteinizing hormone regulate development and rupture.

In dental development, the dental follikel surrounds the developing tooth and contributes to the formation of the supporting tissues, such as the periodontal ligament and alveolar bone.

These follikels are named in many European languages and are equivalents of the English follicle. Knowledge of follikels is relevant in fields including dermatology, reproductive biology, and dentistry.