What is the Difference Between Folliculogenesis and Oogenesis

Both folliculogenesis and oogenesis occur in sexually developed women. The ovarian cycle is the growth and maturation of an oocyte in preparation for fertilization and reproduction in the future. It repeats every 28 days from puberty until menopause and can be mainly divided into two interrelated processes: folliculogenesis and oogenesis.

The key difference between folliculogenesis and oogenesis is that folliculogenesis is the growth and development of ovarian follicles while oogenesis is the production of female gametes.

CONTENTS

1. Overview and Key Difference
2. What is Folliculogenesis  
3. What is Oogenesis
4. Similarities – Folliculogenesis and Oogenesis
5. Folliculogenesis vs Oogenesis in Tabular Form
6. Summary – Folliculogenesis vs Oogenesis
7. FAQ – Folliculogenesis and Oogenesis

What is Folliculogenesis?

Folliculogenesis is the growth and development of ovarian follicles such as oocytes and their supporting cells. This process leads to ovulation of one follicle approximately every 28 days. Meanwhile, other multiple follicles that do not ovulate will die. The death of multiple other ovarian follicles is called atresia, and it can occur at any point during follicular development. There are four major regulatory events involved in folliculogenesis; these include recruitment, preantral follicle development, selection, and atresia.

Figure 01: Folliculogenesis

Folliculogenesis is regulated by the central nervous system, anterior pituitary, and ovary cascade mechanism. Specialized hypothalamic neurons secrete gonadotropin-releasing hormone (GnRH) into the portal blood vessels, which acts on the gonadotrophs to cause the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Later, these hormones act on ovarian follicle cells to control folliculogenesis.

What is Oogenesis?

Gametogenesis in the female is known as oogenesis. It is the differentiation of the ovum. Oogenesis results in the formation of ova in females. The process of oogenesis takes place in three stages: pre-natal (growth of primary oocytes), antral (formation of fluid-filled space called the antrum and secondary follicles) and preovulatory (polar body and secondary oocyte formation).

Figure 02: Oogenesis

The ovulation is the release of a secondary oocyte from ovaries. If the fertilization does not occur, the oocyte degenerates 24 hours after ovulation. Moreover, oogenesis begins in the fetus prior to birth. The hypothalamus releases the gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary. This releases two gonadotropic hormones named FSH (follicle-stimulating hormone) and LH (Luteinising hormone). FSH is the hormone that stimulates follicular growth and oocyte maturation.

Similarities Between Folliculogenesis and Oogenesis

1. 1. Folliculogenesis and oogenesis are the main processes of the ovarian cycle.
   2. Folliculogenesis and oogenesis are two interrelated processes.
   3. Both processes are only observed in women.
   4. These processes are under the control of GnRH, FSH, and LH.
   5. They are extremely important for fertilization and sustenance of life.

Difference Between Folliculogenesis and Oogenesis

Definition

1. Folliculogenesis is the process of creating a follicle that contains the egg cell.
2. Oogenesis is the process of creating an egg cell.

When It Begins

1. Folliculogenesis begins at puberty and continues throughout the reproductive years.
2. Oogenesis begins in the female fetus and is a continuous process throughout the reproductive years.

Process

1. Folliculogenesis describes the process of differentiation of the ovum or egg cell into a cell competent to further develop when fertilized.
2. Oogenesis describes the process of progression of a number of small primordial follicles into large preovulatory follicles.

Key Steps

1. Key steps of folliculogenesis include recruitment, preantral follicle development, selection, and atresia.
2. Key steps of oogenesis include pre-natal, antral, and preovulatory.

The following table summarizes the difference between folliculogenesis and oogenesis.

Summary – Folliculogenesis vs Oogenesis

Folliculogenesis is the process where the primordial follicle is recruited for further development into a Graafian follicle with the potential to either ovulate its egg to be fertilized or to die by atresia, while oogenesis is the process by which mature female gametes or ova, develop from primordial germ cells. This is the basic difference between folliculogenesis and oogenesis.

FAQ: Folliculogenesis and Oogenesis

1. What is the ovarian cycle?

• The ovarian cycle consists of follicular maturation, oogenesis and ovulation. It also involves the alternate fate of the corpus luteum if the egg does not undergo fertilization where it occurs corpus luteum regression and menstruation. Moreover, the first day of menstrual bleeding is designated as the first day of the ovarian cycle.

2. What are the four stages of follicle development?

• The main purpose of folliculogenesis is to produce a single dominant follicle or specialized Graafian follicle from a pool of growing follicles. There are four major regulatory events involved in this process: recruitment, preantral follicle development, selection, and atresia.

3. Which hormone is responsible for folliculogenesis?

• Folliculogenesis is regulated by the central nervous system, anterior pituitary, and ovary cascade mechanism. Folliculogenesis and oocyte maturation are complex processes that require the action of both LH and FSH.

4. What happens in the oogenesis process?

• Oogenesis is the formation of a mature ovum from the oogonia in females. It takes place in the ovaries. It begins in the female fetus and is a continuous process throughout the reproductive years.

5. What is the importance of oogenesis?

• Oogenesis is an important and complex process in mammals. It facilitates the female gamete development for fertilization. It helps for the sustenance of life. Moreover, it is regulated by numerous intra and extra-ovarian factors.

Reference:

1. “Folliculogenesis – An Overview.” ScienceDirect Topics.
2. Gilbert, Scott F. “Oogenesis.” Developmental Biology. 6th Edition., U.S. National Library of Medicine.

Image Courtesy:

1. “Figure 28 02 04” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Oogenesis Labeled” By Alexandra Garcia – Own work (CC BY-SA 4.0) via Commons Wikimedia

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