Lisääntymiskiertokulun

Lisääntymiskiertokulku refers to the cyclical changes that occur in the female reproductive system to prepare for potential pregnancy. In humans, this cycle is primarily regulated by hormones and typically lasts around 28 days, although variations are common.

The cycle begins with menstruation, the shedding of the uterine lining, which occurs when pregnancy has not taken place. Following menstruation, the follicular phase begins. During this phase, follicles in the ovary develop, and one dominant follicle matures, producing estrogen. Estrogen causes the uterine lining, the endometrium, to thicken and become receptive.

Ovulation, the release of a mature egg from the ovary, typically occurs around the midpoint of the cycle, triggered by a surge in luteinizing hormone (LH). After ovulation, the luteal phase begins. The ruptured follicle transforms into the corpus luteum, which produces progesterone. Progesterone further prepares the endometrium for implantation and prevents further ovulation.

If fertilization and implantation occur, the corpus luteum continues to produce hormones to maintain the pregnancy. If pregnancy does not occur, the corpus luteum degenerates, leading to a drop in estrogen and progesterone levels. This hormonal decline triggers menstruation, and the cycle begins anew.

The exact timing and duration of each phase can vary between individuals and even from cycle to cycle. Factors such as stress, illness, and age can influence the regularity of the reproductive cycle. Understanding these changes is fundamental to reproductive health and family planning.