Folikel

Folikel, or follicle in English, is a term used in biology to describe a small sac, cavity, or structure that contains or produces something essential. Several types of follicles occur in different organ systems, each with distinct roles.

Hair follicle: A complex organ located in the skin's dermis that produces hair. It includes the hair bulb, matrix cells, and a dermal papilla with blood vessels. The hair shaft grows through cycles known as anagen (growth), catagen (transition), and telogen (rest). The follicle often associates with a sebaceous gland and a small muscle called the arrector pili, which can cause hair to stand erect.

Ovarian follicle: A sac within the ovary containing an immature oocyte. Follicles mature through stages: primordial, primary, secondary, antral, and Graafian. Follicle-stimulating hormone (FSH) promotes growth, while luteinizing hormone (LH) triggers ovulation. After ovulation, the ruptured follicle forms the corpus luteum, which produces hormones such as estrogen and progesterone.

Dental follicle: Connective tissue surrounding a developing tooth, contributing to the formation and eruption of teeth by supporting the periodontal ligament and related structures.

Lymphoid follicle: A organized cluster of immune cells within lymphoid tissues such as lymph nodes and the spleen. It contains germinal centers where B cells proliferate and differentiate during immune responses.

Plant follicle: In botany, a type of dry fruit that splits open along one side to release seeds, seen in several plant families.

Clinical relevance: Follicles can be affected by conditions such as folliculitis (inflammation of hair follicles) or disorders of folliculogenesis, which can impact hair growth or reproductive processes.