The corpus luteum (CL) is a temporary structure that develops within the ovary. It plays a significant role in the female reproductive cycle, specifically in preparing the body for a potential pregnancy. This gland is fundamental for fertility and early gestation.
How the Corpus Luteum Forms
The corpus luteum develops from the remnants of an ovarian follicle after it releases a mature egg during ovulation. This transformation, known as luteinization, is triggered by a surge in luteinizing hormone (LH) from the pituitary gland. Follicular cells, including granulosa and theca cells, undergo changes, differentiating into luteal cells characterized by their increased size and lipid content. This process happens rapidly, marking the beginning of the luteal phase of the menstrual cycle.
Its Hormonal Functions
The corpus luteum primarily produces progesterone. This hormone prepares the uterine lining (endometrium) for potential implantation. Progesterone makes the endometrium thicker and more vascular, creating a nourishing environment. It also suppresses uterine contractions, providing a stable environment for a developing embryo.
The corpus luteum also produces estrogen and inhibin A. Estrogen also contributes to the preparation of the uterus for implantation. Inhibin A plays a role in a feedback loop to the pituitary gland, helping to regulate the release of other hormones like follicle-stimulating hormone (FSH) and LH. This hormonal activity ensures the proper progression of the menstrual cycle and supports reproductive health.
Its Role in Pregnancy
The corpus luteum performs a crucial function in maintaining early pregnancy. It continues to produce progesterone and estrogen, which are necessary to sustain the endometrial lining. This hormonal support prevents the uterine lining from shedding, preventing miscarriage during the initial weeks of gestation.
If fertilization occurs and an embryo implants, the developing embryo begins to produce human chorionic gonadotropin (hCG). This hormone, which is detected by at-home pregnancy tests, signals the corpus luteum to continue hormone production. The corpus luteum continues its function for the first 7 to 10 weeks of pregnancy, until the placenta develops sufficiently to take over hormone production.
What Happens When Pregnancy Doesn’t Occur
When fertilization and implantation do not happen, the corpus luteum undergoes a process called luteolysis, its degeneration. Without the signal from hCG, the corpus luteum regresses after about 10 to 14 days following ovulation. This regression leads to a drop in the levels of progesterone and estrogen.
The decrease in these hormones causes the uterine lining to break down and shed, resulting in menstruation. This shedding marks the end of one menstrual cycle and the beginning of a new one, preparing the body for another potential ovulation. The degenerated corpus luteum eventually forms a scar-like structure within the ovary called a corpus albicans.
Common Conditions Involving the Corpus Luteum
Sometimes, the corpus luteum may not regress as expected and can fill with fluid, forming a corpus luteum cyst. These are functional ovarian cysts and are generally benign. Most corpus luteum cysts are harmless, often resolving on their own within a few weeks or up to three menstrual cycles, and may not cause symptoms.
Another condition is corpus luteum insufficiency, also known as a luteal phase defect. This occurs when the corpus luteum does not produce adequate progesterone. Insufficient progesterone can make it difficult for the uterine lining to prepare for implantation, potentially leading to challenges with conception or maintaining an early pregnancy.