Reviewer: Leng Jinhua (Peking Union Medical College Hospital)
Author: Dai Yi (Peking Union Medical College Hospital)
Speaking of the endometrium, female friends may not be familiar with it. In fact, menstruation is the result of the periodic shedding of the endometrium (once a month). The endometrium is related to the regularity of menstruation. , more or less quantity, etc. How does the lining of the uterus form menstruation? Why is it so mysterious? Now let’s unravel the “mystery” of the endometrium.
Image source: Zhanku Hailuo
1. From the morphological point of view
Endometrial morphologically can be divided into functional layers (including the dense and spongy layers, two-thirds of the endometrial surface) and basal layers (near the myometrium) one of the intima).
Functional layer: Under the influence of ovarian sex hormones, periodic proliferation, secretion and shedding changes occur, and the periodic shedding of the functional layer forms menstruation.
Basal layer: not affected by ovarian sex hormones and does not undergo periodic changes. After menstruation, it can regenerate and repair the wound surface of the endometrium, and re-form the functional layer of the endometrium.
2. From the perspective of cyclical changes
According to the histological changes of the endometrium, the endometrium can be divided into three stages: proliferative, secretory, and menstrual (see figure below). Take a normal menstrual cycle (28 days) as an example:
Proliferative phase: Corresponding to the 5th to 14th day of menstruation, which corresponds to the mature stage of the follicular phase in the ovarian cycle. Under the action of estrogen, the thickness of the endometrium at this stage changes from 0.5 mm to 0.5 mm. Thickened to 3-5 mm, the epithelium, glands, stroma, and blood vessels on the intimal surface showed proliferative changes.
Secretory phase: Corresponding to the 15th to 28th day of the menstrual cycle, corresponding to the luteal phase in the ovarian cycle, the progesterone and estrogen secreted by the corpus luteum of the ovary make the proliferative endometrium continue to thicken. Thickness up to 10 mm. At this time, the intima is thick and soft, which is rich in nutrients, which is conducive to the implantation and development of fertilized eggs.
Menstrual period: Corresponds to the 1st to 4th day of the menstrual cycle, when estrogen and progesterone decrease, and the endometrial lining that has lost its “nourishing” falls off, resulting in menstruation.
Image source: Zhanku Hailuo
3. From different age groups
Puberty: A girl’s first menstrual cramp, called menarche, is an important sign of puberty. However, girls who have just entered puberty have not yet established a mature menstrual cycle in their bodies, and often have follicles that mature and do not ovulate, so the menstrual cycle is often irregular.
Sexual maturity: At this time, a regular menstrual cycle has been established in the body, and the endometrium undergoes periodic changes under the action of sex hormones. This stage is the most prosperous period of female reproductive function. Also known as the fertile period.
menopausal transition period (a period before menopause): due to the gradual decline of ovarian function, follicles cannot mature and ovulate, so irregular menstruation, clinically more common anovulatory menstruation.
Image source: Zhanku Hailuo
Postmenopause: complete ovarian failure, endometrial atrophy, and menstrual cessation. It is worth noting that if women have vaginal bleeding or discharge after menopause, they should go to the hospital in time to rule out the possibility of endometrial malignant transformation.
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