Dean Cruikshank

Menstrual cycles--special considerations in CF

All girls are born with eggs already produced and stored in her ovaries. Each egg is kept inside a single celled sac, called follicle. At time of her first period or menstrual cycle, she will have approximately 300,000 to 400,000 eggs with the potential to be conceived. However, due to a process called apoptosis, she will lose an average of 1000 follicles per month and this process speeds up after a woman reach age 37 years. By the time of menopause, her number of eggs may be down to only 1000. In reality, we do have a biological clock in terms of our ability to reproduce.

Anatomy and Structures

The first step to understand menstrual cycle is to gain some knowledge about the main organ or body system that help regulars the cycle and the hormones that help to make it happen.

First is the brain: There are two glands inside the brain that participate in regulating the menstrual cycle. These glands are the hypothalamus and the pituitary.

· Hypothalamus secrets a hormone called the gonadotropin releasing hormone (GnRH) to kick start a menstrual cycle.

· Pituitary gland sends out two hormones in sequences to the ovaries to control the ripening and release of an egg each month. These two hormones are follicle stimulating hormone (FSH) and Luteinizing hormone (LH)

Second are the components of the female reproductive system:

· Ovaries: A storage house for the eggs and each egg lives inside a single celled sac called follicles. When a young woman reaches menarche or time for her first menstrual period, the eggs inside the follicle will be stimulated to grow and ripen. During each menstrual cycle, only a few eggs are stimulated to ripen and usually only one egg matures. Once an egg matures, it will burst out of its follicle and ovary and ovulation occurs.

· The fallopian Tubes: These tubes connect each ovary to the uterus. Once an egg matures and bursts out of the ovary, the tiny hair or cilia in the fallopian tube brush the egg toward the uterus.

· The Uterus: This often referred to as the womb. This is where a fertilized egg develops into a fetus. The lining of this organ is subjected to the influence of important hormones namely Estrogen and progesterone. Estrogen helps to build or rebuild the lining of uterus (endometrium) during the first part of a menstrual cycle. Progesterone is released at the second half of the cycle, it makes the lining of the uterus spongy. Should the matured egg become fertilized; it will have a perfect lining to growth. If there is no fertilized egg, this lining is shed and it becomes the discharge of a "period".


Lastly but not least are the hormones: There are seven hormones involves with the reproductive cycle. Four of them come from the ovaries and two of them come from the pituitary gland and one come from the hypothalamus gland. These hormones are

1. Gonadotropin releasing hormone (GnRH) - from the hypothalamus gland that kick starts a menstrual cycle.

2. Follicle stimulating hormone (FSH) - from the pituitary gland that urges follicles (eggs inside the sacs) to grow.

3. Luteinizing Hormone (LH) - from the pituitary gland and it comes in a big burst when the matured egg is about to burst out of the follicle. This happens when ovulation occurs.

4. Estrogen - from the ovaries. This hormone comes in three forms. Estradiol (E2) is the most main one being released during our reproductive years. It comes from inside the follicles that are being stimulated to mature during the first part of a menstrual cycle and it is also the hormone that helps build or rebuild the lining of the uterus to prepare for a fertilized egg to grow. It also have effects on other parts of our body including our sexual organ, hair, breast, bones and brain. However, the level of this hormone will drop to lower than children and man when a woman reached menopause. Another form of Estrogen is called estrone (E1). It is produced by both of the ovaries and the adrenal glands. This is the main estrogen at menopause. It acts on all the same tissues but is weaker than estradiol. It is stored mainly in muscle and fat cells. The third form of Estrogen is estriol (E3). The ovaries least produce it and its level is only high during pregnancy only.

5. Progesterone: a small amount of this hormone is being made by the adrenal gland throughout our lives. This hormone is made most abundantly during the second half of a menstrual cycle called the Luteal phase (the phase immediately follow ovulation) and during pregnancy. It partners with Estradiol in preparing the lining of the uterus for conception. Progesterone acts on every tissue of our body.

6. Testosterone: contrary to most believe, testosterone is not a hormone in male only. Surprisingly, it is rather important to the menstrual cycle. Testosterone provides estradiol to help stimulate the dominant follicle to mature. The presence of testosterone in mid menstrual cycle my actually stimulate our sexual interest during the optimal time for conception.

7. Inhibins: Inhibin A and B. They are made in the ovaries but act on both the ovaries and the pituitary gland to control normal reproductive cycle. Inhibin A is created by the largest follicle and reflects the ovary's ability to ovulated. Inhibin B level reflect the number of follicles left in the ovaries and that is why its level becomes low early at perimenopause when one is still having regular menstrual periods.

Menstrual Cycle: the 2 phases

Day 1 of your period (first day of flow) is the first day of your new menstrual cycle. The whole cycle normally lasts 28 days on average, however there is great variation between women, and it could be as long as 33 days or as short as 24.

The first half of the menstrual cycle is called the Follicular Phase. This phase begins because the level of progesterone hormone in the blood falls, signaling the hypothalamus in the brain to increase the production of GnRH, and at the same time the pituitary gland will send out FSH, and this FSH will work on potentially maturing follicles (around 8-10 that are triggered). Then, only one (or rarely, two) follicles will swell with fluid containing the hormone estradiol. This estradiol will then enter the circulating bloodstream, and stimulate the lining of your uterus (endometrium) to build up and vascularize (grow blood vessels).

Once estradiol reaches its peak in the bloodstream, FSH will decrease and LH will increase to its maximum concentration. This surging of LH cause what is called ovulation. Ovulation is when the follicle bursts to release the egg (ovum) and fluid (mainly hormones).


Now we begin the second stage of the cycle, called Luteal Phase. Once the egg is released outside, now the woman has ovulated. The dominant follicle that has ruptured is now called the corpus luteum, and its job now is to secrete progesterone. As shown above, progesterone is responsible for developing the endometrial lining. Seven days after ovulation, the corpus luteum swells a great deal and then reaches its peak level of progesterone and high levels of estradiol.

The mature egg makes its way down the fallopian tube it is ready to meet a sperm cell and join together (fertilization). If fertilization does occur, estradiol and progesterone levels will remain high throughout the pregnancy. The egg lives in the fallopian tube for 24 hours after ovulation.

If no fertilization takes place, the low levels of FSH and LH will allow the corpus luteum to shrink and both estradiol and progesterone will decrease. The lowered hormone levels in the blood will cause the blood vessels in the endometrial lining to diminish or disappear. The endometrial cells then begin to die as there is no oxygen supply from the loss of the blood vessels. After two days have passed, the endometrial lining will shell blood, tissues and fluid. This makes up the content of the menstrual flow.


This is a wonderful resource for learning more about menstruation and menopause

Transitions through the perimenopausal years: demystifying the journey by Lissa Zala, Andrea Swan, Jerilynn C Prior.