Patient's question:
Why do girls get their period?Doctor's answer:
First, it is essential to understand the structure and physiological functions of the female reproductive organs to explain this issue.The female internal reproductive organs consist of the ovaries, uterus, and fallopian tubes. The primary function of the ovaries is to produce oocytes and synthesize ovarian hormones, while the uterus and fallopian tubes are the reproductive organs. The ovaries contain tens of thousands of follicles, each containing one oocyte.
Before puberty, the follicles are essentially non-functional. During puberty, under the influence of gonadotropin-releasing hormone (GnRH) from the anterior lobe of the pituitary gland, immature follicles gradually develop while synthesizing estrogen. When the follicles mature and ovulate, the follicular wall collapses, the cells enlarge and turn yellow, forming a corpus luteum, which synthesizes estrogen while also producing progesterone.
As the ovaries change, the endometrium is also affected and undergoes corresponding cyclical changes. Estrogen causes the endometrium to thicken, with an increase in the number and size of endometrial cells, as well as the tortuosity of small arteries in the stroma, forming the proliferative phase endometrium. After ovulation, due to the combined effects of estrogen and progesterone, the endometrium becomes edematous, glandular secretion increases significantly, and glycogen accumulates, causing the endometrium to thicken from 1 mm to 6 mm, forming the secretory phase endometrium.
If the released oocyte is fertilized, the fertilized egg travels through the fallopian tube to the uterus for development, resulting in pregnancy. The pregnancy tissue synthesizes human chorionic gonadotropin (hCG), which supports the continued development of the corpus luteum. If the oocyte is not fertilized, around 14 days after ovulation, the corpus luteum atrophies and stops secreting estrogen and progesterone. At this time, the blood vessels in the endometrium contract, leading to necrosis and shedding of the endometrium, causing bleeding and forming menstruation.
Therefore, the length of the menstrual cycle depends on the length of the ovarian cycle, typically ranging from 21 to 30 days, but it varies from person to person, with some having cycles as short as 23 days or as long as 45 days, or even 3 months or 6 months per cycle. As long as it is regular, it is generally considered normal menstruation.
The bleeding period usually lasts 2 to 7 days, and the total amount of menstrual blood loss is typically 30 to 50 ml. Some believe that menstrual blood loss exceeding 80 ml is a pathological condition.