Difference Between Graafian Follicle and Corpus Luteum

The key difference between Graafian follicle and corpus luteum is that Graafian follicle is a specialized follicle that contains the secondary oocyte, while corpus luteum is a temporary gland structure formed after the release of the secondary oocyte from the Graafian follicle.

In biology, folliculogenesis is the maturation of ovarian follicles. Graafian follicle, also known as an antral follicle or tertiary follicle, is an ovarian follicle developed during a certain latter stage of folliculogenesis. Graafian follicle contains the secondary oocyte. Corpus luteum is formed after the release of the secondary oocyte from the Graafian follicle. The corpus luteum is a mass of cells that forms in an ovary. It is responsible for the production of progesterone hormone during early pregnancy.

CONTENTS

1. Overview and Key Difference
2. What is Graafian Follicle 
3. What is Corpus Luteum
4. Similarities Between Graafian Follicle and Corpus Luteum
5. Side by Side Comparison – Graafian Follicle vs Corpus Luteum in Tabular Form
6. Summary

What is Graafian Follicle?

The Graafian follicle is an ovarian follicle matured during a certain stage of folliculogenesis. It is also called the antral follicle. The Graafian follicle has a fluid-filled cavity called the antrum, adjacent to the oocyte. Graafian follicle appears as a mature follicle. There are no novel cells found in the Graafian follicle. The granulosa and theca cells present in the Graafian follicle continue to undergo mitosis. The above process is concomitant with an increase in antrum volume. Follicle-stimulating hormone (FSH) stimulates the development of the Graafian follicle. Graafian follicles can attain a tremendous size depending on the availability of the FSH hormone.

The Graafian follicle’s granulosa cells begin to differentiate into four subtypes based on oocyte-secreted morphogenic gradient. They are the corona radiata; surrounds the zona pellucida, membrana granulose;  that is interior to the basal lamina, periantral; that is adjacent to the antrum, and cumulus oophorus; that connects the membrana and corona radiata granulosa cells together. Theca cells of Graafian follicle contain receptors for LH (luteinizing hormone). LH stimulates the production of androgens (androstenedione) by the theca cells. Androstenedione is aromatized by granulosa cells to produce estrogens.

What is Corpus Luteum?

The Corpus luteum is a temporary endocrine structure involved in ovulation and early pregnancy. In fact, it is a transitory endocrine gland that is a yellow hormone-secreting body. It is formed after the release of the secondary oocyte from the Graafian follicle. During ovulation, a dominant mature follicle releases an egg. After the release of the egg and subsequent fertilization, the follicle seals off itself. Therefore, it forms the corpus luteum. Corpus luteum secretes a hormone called progesterone during early pregnancy. The Corpus luteum will continue producing progesterone until the fetus is producing an adequate level to sustain the pregnancy. It usually occurs between 7-9 weeks of the pregnancy. Progesterone is very important in early pregnancy. Progesterone allows the uterus to grow, and it supports the growth of the lining of the uterus.

Moreover, the Corpus luteum is also supported by the hormone human chorionic gonadotrophin (HCG). When fertilization does not occur, the corpus luteum will break down. This will decline the estrogen and progesterone levels. It leads to the start of another menstrual period.

What are the Similarities Between Graafian Follicle and Corpus Luteum?

• Graafian follicle and corpus luteum are two structures produced by the ovary.
• Both structures secrete hormones.
• They are very important for female reproductive function.
• Structurally, both are a mass of cells.

What is the Difference Between Graafian Follicle and Corpus Luteum?

The graafian follicle is the follicle that contains the secondary oocyte in the ovary. Meanwhile, the Corpus luteum is a temporary endocrine gland formed after the release of the secondary oocyte from the Graafian follicle. Thus, this is the key difference between Graafian follicle and corpus luteum. Moreover, the Graafian follicle secretes estrogen while the corpus luteum secretes progesterone. Besides, FSH regulates the development and maintenance of the Graafian follicle, while HCG regulates the development and maintenance of the corpus luteum. So, this is another significant difference between Graafian follicle and corpus luteum.

The following infographic lists the differences between Graafian follicle and corpus luteum in tabular form.

Summary – Graafian Follicle vs Corpus Luteum

The Graafian follicle is the follicle that contains the secondary oocyte. The cells in the Graafian follicle contribute to producing estrogen. Corpus luteum is formed after the release of the secondary oocyte from the Graafian follicle. It is a yellow, hormone-secreting body. The mass of cells in the corpus luteum produces the hormone progesterone during early pregnancy. Thus, this summarizes the difference between Graafian follicle and corpus luteum.

Reference:

1. “Antral Follicle.” Wikipedia, Wikimedia Foundation, 12 Dec. 2020, Available here.
2. “Corpus Luteum: Function, Formation, and Cysts.” Medical News Today, MediLexicon International, Available here.

Image Courtesy:

1. “Graafian follicle” By Dr. Roshan Nasimudeen – Department of Pathology, Government Medical College, Kozikode (CC BY-SA 3.0) via Commons Wikimedia
2. “334238 1 En 7 Fig1 HTML” By Dmcmdissa – Own work (CC BY-SA 4.0) via Commons Wikimedia