follikkelivaihe

Follikkelivaihe refers to the initial stage of the ovarian cycle in the human menstrual cycle. This phase begins on the first day of menstruation and lasts until ovulation. During the follikkelivaihe, the pituitary gland secretes follicle-stimulating hormone (FSH), which stimulates the development of several ovarian follicles. Each follicle contains an immature egg. As the follicles grow, one dominant follicle typically emerges and matures further, while the others degenerate. This dominant follicle produces increasing amounts of estrogen. Estrogen levels rise, which in turn causes the uterine lining, the endometrium, to thicken in preparation for a potential pregnancy. The rising estrogen also triggers a surge in luteinizing hormone (LH) from the pituitary gland, which ultimately leads to ovulation. The duration of the follikkelivaihe can vary between individuals and from cycle to cycle, but it generally lasts around 10 to 14 days.