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💀anatomy and physiology i review

Primary Follicle

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

A primary follicle is an early stage of follicular development in the ovary, which contains an immature oocyte (egg cell) surrounded by a single layer of granulosa cells. It is the first stage in the maturation process of a female's egg before ovulation.

5 Must Know Facts For Your Next Test

  1. Primary follicles are the earliest stage of follicular development, arising from primordial follicles in the ovary.
  2. The primary follicle is characterized by a single layer of cuboidal granulosa cells surrounding the immature oocyte.
  3. Follicle-stimulating hormone (FSH) from the pituitary gland stimulates the growth and development of primary follicles.
  4. As the primary follicle matures, it develops multiple layers of granulosa cells and the oocyte increases in size.
  5. Primary follicles must progress through several developmental stages, including secondary and antral follicles, before they can ovulate and release a mature egg.

Review Questions

  • Describe the structure and function of a primary follicle in the ovary.
    • A primary follicle is the earliest stage of follicular development in the ovary. It consists of an immature oocyte (egg cell) surrounded by a single layer of cuboidal granulosa cells. The granulosa cells provide nutrients and support for the growing oocyte. Follicle-stimulating hormone (FSH) from the pituitary gland stimulates the growth and development of primary follicles, which must progress through several more advanced stages before they can ovulate and release a mature egg.
  • Explain the role of primary follicles in the process of folliculogenesis.
    • Primary follicles are the first step in the process of folliculogenesis, which is the development and maturation of ovarian follicles. They arise from primordial follicles and contain an immature oocyte surrounded by a single layer of granulosa cells. As primary follicles mature, they progress through secondary and antral follicle stages, during which the granulosa cell layer proliferates, the oocyte grows larger, and a fluid-filled cavity called the antrum forms. This maturation process is essential for preparing the oocyte for ovulation and fertilization.
  • Analyze how the transition from primary to secondary follicles is regulated and what changes occur during this stage of development.
    • The transition from primary to secondary follicles is regulated by complex hormonal signaling, primarily involving follicle-stimulating hormone (FSH) from the pituitary gland. As primary follicles develop, the granulosa cells proliferate to form multiple layers, and the oocyte increases in size. This morphological change, along with increased secretion of estrogen by the granulosa cells, signals the follicle to progress to the secondary stage. At this point, the follicle acquires a distinct theca cell layer outside the granulosa cells, and the antrum (fluid-filled cavity) begins to form. These structural and functional changes prepare the follicle for the final stages of maturation and ovulation of the oocyte.