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Corpus Luteum: Growth, Structure & Function

Corpus Luteum: Growth, Structure & Function

The final active stage of an ovarian follicle’s lifecycle is called corpus luteum (also known as corpora lutea), and without it, maintaining early pregnancy cannot be easy. Unfortunately, the corpus luteum does not get enough credit for the vital role it plays in the menstrual cycle and pregnancy. It forms from the empty follicle that the ovulated egg leaves behind after ovulation.

Your ovary contains many follicles, which are tiny sacs filled with fluid. Each follicle contains an oocyte or immature egg. During the first 2 weeks of your menstrual cycle, the hormones that the hypothalamus regulates and the pituitary gland releases will trigger some of these follicles to grow. This is how the eggs in the follicles mature in preparation for ovulation.

Ultimately, the follicles become dominant, and that’s where the ovulated egg comes from in every other cycle. The eggs will burst from the follicle and leave behind an inhabited shell of cells. After the egg leaves, the cells go through a change. They collapse in on themselves and change the hormones they secrete. The collapsed follicle is what forms the corpus luteum. If you would like to know more about the role of the corpus luteum, this post is for you. Keep reading to learn more and share this post with other women in Australia.

 How Does the Corpus Luteum Affect Fertility?
How Does the Corpus Luteum Affect Fertility?

The corpus luteum and production of hormones

While corpus luteum is a temporary loan structure, its role cannot be ignored. It helps in secreting the progesterone and estrogen hormones which prepare the body for conception in case the ovulated egg is fertilized. The hormones assist in building up the uterus lining, creating a nice bed for the fertilized egg to implant into. The hormones also help maintain this lining throughout the pregnancy period.

In case the conception doesn’t occur, the corpus luteum starts to break down, which causes a drop in estrogen and progesterone hormone hence triggering menstruation. The reproductive cycle begins all over again after the periods.

Corpus luteum role in the menstrual cycle

To understand how the corpus luteum works, you need to learn more about the ovulation process. Generally, there are two primary phases in each menstrual cycle; the follicular and luteal phases. In the follicle phase, a selected number of follicles will mature, but only one of them will release an egg. During the luteal phase or post-ovulation, the body will prepare to accept the fertilized egg/ embryo.

Before ovulation occurs, you will experience a luteinizing hormone surge and a positive ovulation test, a hormone that plays an essential role in ovulation and what happens after you ovulate. When you are about to ovulate, the luteinizing hormone triggers a follicle and speeds up the growth of the developing egg. The hormone also triggers an enzyme to break down the external walls of the follicle where the egg is being developed. Once the egg reaches its full maturity, the follicle walls will burst open, releasing the mature egg in the process we call ovulation.

Immediately after the egg is released, the luteinizing hormone continues to affect the cellular structure of the follicle that released the egg. Before ovulation, the theca and granulosa cells found in the follicle produce the estrogen hormone. After ovulation, however, the luteinizing hormone triggers these cells to change, so they can start producing the progesterone hormone.

The progesterone hormone plays a vital role in the luteal phase. To begin with, it signals the hypothalamus and pituitary gland in your brain to start slowing down the production of the follicle-stimulating hormone (FSH), luteinizing hormone, and gonadotropin-releasing hormone. This ensures that other follicles do not develop further in preparation for ovulation.

The progesterone hormone also prepares the uterine lining or endometrium by triggering it to secrete proteins. The proteins help maintain the endometrium and create a nourishing environment for the embryo. Another role the progesterone hormone plays is to signal the breast tissue to start preparing for milk production. This is the reason why the breast becomes tender after ovulation and before having your periods.

Corpus luteum and conception

If the ovulated egg is fertilized and the embryo implants itself into the uterus, a clear placenta will form. The placenta is responsible for releasing the pregnancy hormone hCG (this is the hormone that pregnancy tests detect in the urine sample).

Due to the presence of the hCG hormone, the corpus luteum is signalled to continue producing more progesterone. Progesterone will prevent the endometrium from being broken down and prevent ovulation. But if pregnancy does not occur, corpus luteum disintegrates slowly, a process that happens within 10 to 12 days after ovulation or 2-3 days before menstruation begins.

While the corpus luteum breaks down, its cells will stop producing progesterone hormone. The dropping levels of progesterone will cause the endometrium to break down, allowing menstruation to begin. Reduced levels of progesterone also signal the hypothalamus and pituitary glands to produce more luteinizing hormone, follicle-stimulating hormone, and gonadotropin-releasing hormone. This will restart your menstrual cycle, and the follicular phase will start again.

The corpus albicans

Every time the corpus luteum breaks down, scar tissue remains behind. The scar tissue is made up of cartilage, also known as corpus albicans. Generally, the corpus luteum is yellowish, but the corpus albicans is white.

Corpus albicans stay on the ovary for several months until it’s broken down. Unlike corpus luteum, corpus albicans do not act like other glands or secrete hormones.

Corpus luteum cysts

As mentioned earlier corpus luteum forms an open follicle after releasing an egg. In some cases, the corpus luteum opening gets sealed. Fluids usually fill the cavity forming a cyst. This form of cyst is known as a functional cyst, and they are not cancerous and can go away naturally. Corpus luteum cysts are harmless and painless.

A corpus luteal cyst may be spotted if you are undergoing fertility treatment, and an ultrasound is done at the beginning of the cycle. Depending on the cyst size, your doctor may delay your treatment to drain the cyst first.

If you develop a corpus luteum cyst regularly, your fertility doctor may opt to put you on contraceptives before starting the treatment. This will prevent ovulation in the month before treatment hence preventing a potential formation of a cyst.

If an ultrasound is done and the cyst appears to be growing, large, or painful, it may need to be removed or drained surgically.

Does corpus luteum cyst mean pregnancy?
Does corpus luteum cyst mean pregnancy?

Corpora Lutea cyst pain

Although it’s rare, a corpus luteum cyst can sometimes cause mild discomfort. This may come as a short sharp pain on one side or more constant pain on one side of the pelvic area. If you are pregnant, the pain may continue for longer during the first few weeks of your pregnancy. If you didn’t conceive, the pain will likely go away in a few days after the periods start.

Provided you don’t experience severe pain or have worrisome symptoms such as fever or vomiting, you’ll have nothing to worry about. You can always discuss this with your healthcare provider, but this does not mean that you need medical assistance right away.

But if you experience unusual bleeding or severe pain, inform your provider or visit the nearest emergency room because ovarian torsion can be severe.

Corpus luteum defect or deficiency

Sometimes, the corpus luteum may fail to produce enough progesterone, leading to abnormal spotting. Low progesterone levels can also lead to light spotting, which will make you think that you are not pregnant when you actually are.

When the levels of progesterone are low after ovulation, it means that you have a corpus luteum defect or luteal phase defect. The deficiency of corpus luteum might increase early miscarriage risks. The treatment for this might include taking progesterone supplements or using fertility drugs like clomiphene, or getting hCG injections.

However, there isn’t any current evidence to show that these treatments will help. The corpus luteum defect diagnosis is also unclear and controversial so if you are in Australia, consult with your fertility doctor first to know your options. Based on the current evidence, luteal phase defect isn’t recognized as a specific infertility cause.

The corpus luteum is created from a follicle that holds a mature ovum. The corpus luteum is a vital small temporary organ.