Where does menstrual bleeding occur?

Menstruation is basically a physiological phenomenon that exists in every normal female body, and most women do not want this phenomenon to exist in their bodies. Because menstruation can make women's bodies weak and even cause some gynecological diseases. Women will experience bleeding from their lower body during menstruation. People who don't know much about the female body structure may even wonder where the menstrual blood comes from?

What causes menstrual bleeding?

1. What causes menstrual bleeding?

Menstruation is vaginal bleeding caused by the periodic shedding of the endometrium due to cyclical changes in ovarian hormones. After puberty, the ovaries gradually develop under the stimulation of gonadotropin secreted by the hypothalamus-pituitary gland. Under the action of pituitary follicle-stimulating hormone, the follicles gradually grow, mature, and secrete a large amount of estrogen. Under the action of estrogen, the endometrium proliferates and thickens, showing proliferative changes. Under the action of luteinizing hormone, the mature follicle ruptures and discharges the egg. After ovulation, the follicle forms a corpus luteum, and the luteal cells secrete progesterone. Under the combined action of estrogen and progesterone, the endometrium further proliferates and shows secretory phase changes due to the secretion of its glandular epithelial cells. If the egg is not fertilized, the corpus luteum begins to shrink. The average lifespan of the corpus luteum is 14 days. After the corpus luteum atrophies, the levels of ovarian estrogen and progesterone drop rapidly, causing the endometrium to lose support and atrophy, and also fall off due to ischemia and necrosis, resulting in vaginal bleeding, which is commonly known as menstruation.

The first onset of menstruation is called menarche. The age of menarche is mostly between 13 and 15 years old, and its timing is affected by various internal and external factors, such as climate, personal physique, nutritional status, etc.

2. What are the periods for menstruation to occur?

Proliferation phase. Before the ovaries produce mature eggs, they begin to secrete estrogen, stimulating the thickening of the endometrium.

Secretory phase. When a follicle in the ovary matures and ruptures to release the egg, the follicle itself becomes a corpus luteum. The progesterone it secretes causes the endometrium to continue to thicken and become congested in order to prepare for the reception and nourishment of the fertilized egg. Because the secretory glands of the endometrium are elongated and filled with nutrient fluid during this period, it is called the secretory phase.

Menstrual period. If the egg is not fertilized after being released, the corpus luteum will slowly shrink. At this time, the ovaries can only secrete a small amount of estrogen and progesterone, so that the endometrium can no longer maintain its current state and falls off. The blood and broken mucosa are discharged from the uterine cavity through the vagina. This is "menstruation". This type of menstrual blood discharge is regular, with one flow occurring once a month, hence the name “menstruation”. Menstruation plays a cleaning role in the shedding of the endometrium.