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The female reproductive cycle can be separated into three phases: the follicular phase, the ovulatory period and the luteal phase (5).
The follicular phase is the phase where an immature ovum is allowed to develop. From gonadotrophin releasing hormone (GnRH) in the hypothalamus, both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted from the pituitary gland. This early point in the menstrual cycle is the only point where FSH is higher than LH (5).
The latter two hormones go to the ovaries and allow the immature ovum to develop; the ovum's development allows for it to produce estradiol, progesterone and andrgoen (6,7). These estradiol levels continue to rise and will cause more GnRH to be released. This second surge of GnRH causes a spike in both LH and FSH, and is the signal for the ovum to be released from the follicle. This is the process of ovulation and it signals the start of the luteal phase (6).
The ovum will move through the fallopian tubes and into the uterus while the follicle that once held it becomes the corpus luteum. It is this secondary structure that continues to make estradiol and will introduce more progesterone into the picture. The estrogen causes the endometrial lining to thicken and the progesterone allows this thickened wall to be maintained. These hormones will also stop the production of FSH and LH (6).
Eventually, the corpus luteum dies and the hormones it was producing decrease. When estrogen and progesterone fall, the uterus' lining sloughs off and menstruation begins. Now, FSH and LH can begin to rise again, as they are unopposed; the cycle can begin again.
The follicular phase is the phase where an immature ovum is allowed to develop. From gonadotrophin releasing hormone (GnRH) in the hypothalamus, both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted from the pituitary gland. This early point in the menstrual cycle is the only point where FSH is higher than LH (5).
The latter two hormones go to the ovaries and allow the immature ovum to develop; the ovum's development allows for it to produce estradiol, progesterone and andrgoen (6,7). These estradiol levels continue to rise and will cause more GnRH to be released. This second surge of GnRH causes a spike in both LH and FSH, and is the signal for the ovum to be released from the follicle. This is the process of ovulation and it signals the start of the luteal phase (6).
The ovum will move through the fallopian tubes and into the uterus while the follicle that once held it becomes the corpus luteum. It is this secondary structure that continues to make estradiol and will introduce more progesterone into the picture. The estrogen causes the endometrial lining to thicken and the progesterone allows this thickened wall to be maintained. These hormones will also stop the production of FSH and LH (6).
Eventually, the corpus luteum dies and the hormones it was producing decrease. When estrogen and progesterone fall, the uterus' lining sloughs off and menstruation begins. Now, FSH and LH can begin to rise again, as they are unopposed; the cycle can begin again.