An ovarian follicle is the basic – fundamental unit of the female reproductive biology, and is composed of spherical aggregations of cells. A follicle contains one oocyte. The follicle is periodically instigated to grow and develop, culminating in ovulation. Eggs develop only once a month, i.e. once every menstrual cycle; a woman commences puberty with around 400,000 follicles.
Levels of oestrogen hormone peak towards the end of the follicular phase, which triggers a surge in the levels of the luteinizing hormone (LH) and follicle stimulating hormone (FSH). This tends to last from 24 – 36 hours, and causes a rupturing of the ovarian follicle, and results in the oocyte to be released from the ovary.
What Happens To The Ruptured Follicle After Ovulation?
Ovulation is characterized by a rupturing of the ovarian follicles and release of the ovarian cells. It is that phase of the menstrual cycle, when an egg is released from the ovaries. After ovulation, during the luteal phase, the egg is available to be fertilized by a sperm.
Ovulation is governed by the hypothalamus and the hormones, luteinizing hormone and follicle stimulating hormone released by the anterior pituitary gland. In the pre ovulatory phase, the follicle undergoes a series of transformations and changes and the primary oocyte is released.
Ovulation is set off by a raise in the levels of the luteinizing hormone and the follicle stimulating hormone. In the post ovulatory phase, the secondary oocyte travels via the fallopian tubes, and in to the uterus. In case fertilization takes place with a sperm, the ovum gets implanted in to the endometrium of the uterus.
In the follicular phase, the ovarian follicles mature. The phase lasts from the commencement of the menstruation to the start of ovulation. An increase in the cumulus cell number takes place, which results in an increase in the antrum fluid. This antrum fluid forms a big bulge at the surface of the ovary, called the ‘blister’.
Levels of the estrogen hormone rise; and cause a surge in the levels of luteinizing hormone as well as follicle stimulating hormone, which results in the rupturing of the ovarian follicles, triggering the oocyte to be released from the ovary.
Through a cascade triggered by the luteinizing hormone, proteolytic enzymes are released by the follicle which destroy the follicular tissue at the site of the ‘blister’, and form a hole. The oocyte complex then leaves the ruptured follicle and moves out into the fallopian tube and then goes in to the uterus.
With this, the follicle proper has met the conclusion of its lifespan. Without the oocyte, the follicle will fold inwards on itself, and it forms what is known as the corpus luteum. The corpus luteum releases hormones estrogen and progesterone. The action of progesterone increases the basal body temperature by one quarter to one half degree Celsius. The corpus luteum continues this hormone releasing action for the rest of the menstrual cycle, helping maintain the endometrial lining, before disintegrating in to scar tissue during menses.