What is the Difference Between Graafian Follicle and Corpus Luteum

The main difference between Graafian follicle and corpus luteum is that the Graafian follicle is the tertiary vesicular follicle or the mature ovarian follicle whereas the corpus luteum is the ruptured Graafian follicle to release the egg.

Generally, the Graafian follicle and corpus luteum are two end-stage structures of the ovarian follicle, a roughly spheroid cellular aggregation set found in the ovaries. Usually, it secretes hormones, influencing the stages of the menstrual cycle.

Key Areas Covered

1. What are Graafian Follicle
– Definition, Structure, Function
2. What are Corpus Luteum
– Definition, Structure, Function
3. Similarities Between Graafian Follicle and Corpus Luteum
– Outline of Common Features
4. Difference Between Graafian Follicle and Corpus Luteum
– Comparison of Key Differences

Key Terms

Corpus Luteum, Graafian Follicle

What is Graafian Follicle

The Graafian follicle is the tertiary follicle that develops from the secondary follicle. It has completed the first mitotic division and the egg or the oocyte is a secondary oocyte that is going to undergo the second mitotic division. During the first mitotic division, most of the cytoplasm goes into one of the two daughter cells and the other cell becomes a polar body. In the meanwhile, follicular fluid fills a single space called the antrum surrounded by follicular cells called membrane granulosa. Here, granulosa cells surround the oocyte and project it into the antrum.

Figure 1: Graafian Follicle

Furthermore, there are two layers of theca; theca interna and theca externa. Here, theca externa merges with the surrounding stroma cells. In ovulation, the oocyte, zona pellucida, and the follicular cells that surround the oocyte enter into the fallopian tube. The oocyte undergoes a second mitotic division after the release from the Graafian follicle.

What is Corpus Luteum

The Corpus luteum is the ruptured and collapsed Graafian follicle. Also, the collapsed Graafian follicle contains a blood clot and granulosa cells that are enlarged and become vesicular. Further, these granulosa cells become folded and are called granulosa lutein cells. Theca interna cells fill the space between folds. However, these cells also become glandular and are known as theca lutein cells.

Figure 2: Corpus Luteum

Moreover, granulosa lutein cells start to secrete progesterone. The corpus luteum also secretes estrogen, which inhibits follicle-stimulating hormone (FSH), and relaxin, which relaxes the fibrocartilage of the pubic symphysis. If the pregnancy does not occur, the corpus luteum degenerates into the corpus albicans and the levels of oestrogen and progesterone fall, thus, allowing the release of FSH and LH. In contrast, if pregnancy occurs, the corpus luteum persists.

Similarities Between Graafian Follicle and Corpus Luteum

• Graafian follicle and the corpus luteum are two end-stages of the ovarian follicle.
• Both occur inside the ovary.
• Both secrete hormones.
• These structures continuously develop on a regular basis in the menstrual cycle.

Difference Between Graafian Follicle and Corpus Luteum

Definition

Graafian follicle refers to a fluid-filled structure in the mammalian ovary within which an ovum develops prior to ovulation while corpus luteum refers to a hormone-secreting structure that develops in an ovary after an ovum has been discharged but degenerates after a few days unless pregnancy has begun.

Significance

Usually, the Graafian follicle is the tertiary vesicular follicle while the corpus luteum is the ruptured Graafian follicle to release the egg.

Structure

The Graafian follicle is a heterogeneous family of relatively large follicles (400 μm to >2 cm at ovulation) that display an antrum containing follicular fluid, or liquor folliculi while there are two main types of cells in corpus luteum: follicular theca cells and follicular granulosa cells.

Occurrence of the Egg

The Graafian follicle contains the egg while the corpus luteum does not contain the egg.

Ovulation

Graafian follicle occurs before ovulation while the corpus luteum occurs after ovulation.

Function

Graafian follicle allows the maturation and release of a fertilizable oocyte while the corpus luteum releases progesterone to prepare the uterus for pregnancy.

Hormones

Graafian follicle secretes estrogen while the corpus luteum secretes progesterone.

Conclusion

In brief, the Graafian follicle and corpus luteum are two structures developed from the ovarian follicle. Usually, the Graafian follicle is the tertiary vesicular follicle that contains the egg. Therefore, it occurs before ovulation. Importantly, the Graafian follicle secretes estrogen and it allows the egg to mature inside the follicle. In contrast, the corpus luteum is the remains of the Graafian follicle after the release of the egg. Also, the main function of the corpus luteum is to release progesterone, preparing the uterus for pregnancy. Therefore, the main difference between Graafian follicle and corpus luteum is the structure and function.

References:

1. Paxton, Steve, et al. “The Leeds Histology Guide.” Home: The Histology Guide, 1 Jan. 1970.

Image Courtesy:

1. “Graafian Follicle, Human Ovary (3595817584)” By Ed Uthman – Own work (CC BY 2.0) via Commons Wikimedia
2. “334238 1 En 7 Fig1 HTML” By Dmcmdissa – Own Work (CC BY-SA 4.0) via Commons Wikimedia