Menstrual Cycle

By: Erin Martin

Explain how hormone levels fluctuate throughout the cycle:

Hormone level LH is low until it reaches its peak during mid-cycle and then it begins to decrease again to low levels. Hormone level FSH is higher than LH until mid-cycle and then becomes lower from mid-cycle to end of cycle. Hormone level progesterone remains low until mid-cycle then peaks during the luteal phase near of the menstrual cycle. Hormone level Estrogen reaches its peak during mid-cycle and is lower than progesterone from mid-cycle to the end of the menstrual cycle.

Description of how endometrial lining changes due to hormones:

In follicular phase the estrogen and progesterone slowly rise until mid-cycle when peak. The endometrial lining is prepared by high estrogen levels for egg implantation. Progesterone levels decrease and the lining sloughs for menstruation. If pregnancy occurs progesterone levels do not decrease as fast and no menstruation.

Description of follicular development based on hormones:

The increase in FSH stimulates the ovarian follicle to develop in time for development of egg. LH carries out different roles in the two halves of the menstrual cycle. In weeks one to two of the cycle, LH is required to stimulate the ovarian follicles in the ovary to produce the female sex hormone, estrogen. Around day 14 of the cycle, a surge in LH levels causes the ovarian follicle to tear and release a mature oocyte (egg) from the ovary, a process called ovulation. For the remainder of the cycle, which are weeks three to four, the remnants of the ovarian follicle form a corpus luteum. Luteinising hormone stimulates the corpus luteum to produce progesterone which is required to support the early stages of pregnancy, if fertilization occurs.

If a pregnancy occurs, explanation of how hormone levels change:

If the egg is fertilized the estrogen level is going to stay high and is high throughout pregnancy. The progesterone level will drop initially so that you don't menstruate then it slowly rises until delivery when it is very high. Once conception occurs LH and FSH are not active during pregnancy.

If a pregnancy occurs, explanation of how the endometrial lining changes:

The lining remains mature so that the fertilized egg can implant in the uterus. The progesterone levels allow the lining of the uterus to nourish the fertilized egg without a fertilized egg the lining would slough.