The Menstrual Cycles

By Amy Demone and Anna Naylor

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Unlike the Male reproductive system, the women is born with only so many follicles (structures in the ovary that contain the egg and secrete estrogen), which constantly decline once your period has started.

Follicle development is controlled by a hormone produced in the pituitary gland. When your menstrual cycle begins, your estrogen level is low, so your hypothalamus sends a message to your pituitary gland to send our follicle stimulating hormone (FSH). This hormone triggers a few of your follicles to develop into mature eggs.

Follicle Stimulating Hormone (FSH) a beta chain of 115 amino acids, which gives it its

unique properties. Synthesis and release of FSH is triggered by the

arrival from the hypothalamus of Gonadotropin-releasing Hormone (GnRH) telling the pituitary gland that the estrogen level is low.

In sexually-mature females, FSH (assisted by LH) acts on the follicle to stimulate it to develop follicles into mature eggs.

Lutenizing Hormone (LH) a beta chain of 115 amino acids

LH in sexually-mature females: a surge of LH triggers the completion of meiosis I of the egg and its release (ovulation) in the middle of the cycle. It also stimulates the now-empty follicle to develop into the corpus luteum, which secretes progesterone during the latter half of the menstrual cycle.

Estrogen Follicle-stimulating hormone (FSH) and luteinizing

hormone (LH) stimulate the production of estrogen in the ovaries.

They promote the development of female secondary sex characteristics, such as breasts, and are also involved in the thickening of the uterine lining and other aspects of regulating the menstrual cycle.

Increase uterine growth. Reduce muscle mass.

Nutrient follicle cells surround the primary oocyte as it begins to divide. As the primary oocyte undergoes meiosis 1, the majority of the cytoplasm and nutrients move to form a second oocyte.

The original cell dies, and the the new oocyte (containg 23 chromosomes) is released when mature. It will break through ovary wall and begin its journey down the fallopian tube for fertilization.

The high level of estrogen will tell the hypothalamus and pituitary gland that there is a mature egg. A luteinizing hormone (LH) is then released which helps the mature egg through the ovary wall.

Video Links:http://www.mayoclinic.com/health/ovulation/MM00108

http://pennhealth.com/health_info/pregnancy/000153.htm

This process is known as ovulation. The follicles that surrounded the mature egg will transform into the corpus luteum and releases hormones needed for pregnancy.

The corpus luteum will release progesterone that helps thicken and prepare the uterine lining for implantation. If the mature egg is not fertilized though, the extra tissue, blood, and egg will exit your body, and the cycle will begin again.

The Menstrual Cycle The menstrual cycle is repeated throughout

a women’s reproductive lifetime. Takes an average of 28 days to complete. There are 4 phases:

The Flow Phase The Follicular Phase The Ovulatory Phase The Luteal Phase

Flow Phase The beginning of the menstrual cycle

begins with the flow phase. This is when the shedding of the endometrium happens. This is the only part of the menstrual cycle that can be determined externally. It’s the reason that the flow phase is what starts the beginning of the cycle. There are approximately five days required for the uterus to shed the endometrium.

The Follicular Phase The follicular phase is when the

development of follicles within the ovary occurs. During the cell’s development, the hormone estrogen is secreted. The follicles continue to develop and the estrogen concentration in the blood increases. This phase usually lasts between day 6 and day 13 of the menstrual cycle.

The Ovulatory phase The ovulatory phase is when the egg bursts

from the ovary and follicular cells differentiate into the corpus luteal.

The Corpus Luteal is a mass of follicle cells that forms within the ovary after ovulation; secrets hormones – estrogen and progesterone.

The Luteal Phase The last phase of the menstrual cycle is the

luteal phase. It lasts the longest, from day 15 to day 28. The luteal phase begins with the

development of the corpus luteum.

The Luteal Phase …continued

The development of the corpus luteum is when estrogen levels begins to decline when the oocyte leaves the ovary, but are restored somewhat when the corpus leutum forms. The progesterone continues to stimulate the endometrium and prepares the uterus for an embryo. It also inhibits uterine contractions and prevents them. When progesterone levels fall the uterine contractions would begin.

The Luteal Phase . . . continued The luteal phase prepares the uterus to receive a

fertilized egg. If fertilization of an ovum does not occur, the concentrations of estrogen and progesterone will decrease – which causes weak uterine contractions. The weak contractions make the endometrium pull away from the uterine wall. The shedding of the endometrium marks the beginning of the menstrual cycle, so therefore the cycle starts over again.

The Regulating Glands The hypothalamus – pituary complex is

what regulates the production of estrogen and progesterone.

Female follicle-stimulating hormone (FSH) and lutenizing hormone (LH) are what regulates the control of estrogen and progesterone.

Too much . . . Too little? Severe symptoms of PMS, pre-menopause

or menopause that don’t respond to a program of increased support for your body within a month or two is a sign that you may have steadily higher than normal levels of estrogen.

Too much estrogen in your body will cause tiredness

Too much … Too little? If there is not enough progesterone in your

body will cause irregular and heavy menstrual bleeding. As well as vaginal dryness.

Too much progesterone in your body will cause tiredness and sometimes sedation.

FUN FACT!

Estrogen may be used to help cure prostate cancer in males!