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Menstrual Cycle Phases

Learn how understanding the different phases of your menstrual cycle can help you better manage your period and improve your overall health.

Review of Menstrual Cycle Phases

The menstrual cycle is a normal and necessary part of a woman's reproductive system. It is a complex system that involves hormones, the uterus, the ovaries, and other tissues and organs in the body. To better understand the menstrual cycle, it is useful to break it down into four distinct phases. These are the follicular phase, ovulatory phase, luteal phase, and the menstrual phase. Each of these phases has different histological characteristics, which are discussed in this review.

Follicular Phase

The follicular phase is the first phase of the menstrual cycle and is typically characterized by the growth of a follicle in the ovary. In the follicular phase, the endometrium of the uterus undergoes a series of histological changes. The first of these is the proliferation of the endometrium, which is caused by an increase in estrogen levels. This results in the endometrium becoming thicker and more vascularized, which can be seen under the microscope. A second histological change in the endometrium during the follicular phase is the presence of an increased number of glands. These glands are responsible for secreting substances that will help to nourish the egg when it is released from the ovary.

Ovulatory Phase

The ovulatory phase is the second phase of the menstrual cycle and is characterized by the release of an egg from the ovary. This is caused by a surge in luteinizing hormone, which causes the follicle to rupture and release the egg. Histologically, the endometrium continues to thicken and the number of glands increases, but the most prominent change is the presence of a large number of cilia in the endometrium. These cilia are responsible for helping the egg to travel through the uterus towards the fallopian tubes.

Luteal Phase

The luteal phase is the third phase of the menstrual cycle and is characterized by the formation of the corpus luteum in the ovary. The corpus luteum forms after the egg is released and is responsible for producing progesterone, which helps to prepare the uterus for implantation of the egg. Histologically, the endometrium continues to thicken and the number of glands increases. Additionally, the endometrium begins to show signs of secretory activity, which can be seen under the microscope.

Menstrual Phase

The menstrual phase is the fourth and final phase of the menstrual cycle and is characterized by the shedding of the endometrium. This is caused by a decrease in progesterone, which causes the endometrium to break down and be shed from the body. Histologically, the endometrium is significantly thinner and lacks the secretory activity that was present in the luteal phase. Additionally, the number of glands is reduced and the presence of cilia is no longer seen.


In conclusion, the menstrual cycle is a complex process that involves a number of different histological changes. By breaking the cycle down into four distinct phases, it is possible to better understand the histological changes that occur and how they relate to the overall process. Understanding the histology of the menstrual cycle can help to provide insight into the biology of reproductive health and can help diagnose and treat any potential issues.

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