Name: Date: Period:

Menstrual Cycle

Background: When a human female is born, her ovaries already contain all the immature eggs that

will later mature and produce functional eggs during her lifetime. Eggs usually begin to mature

between the ages of 12 and 14, when a release of hormones triggers puberty and a young woman

reaches sexual maturity. Most commonly, eggs mature every 28 days or so. They usually mature

one at a time, in alternating ovaries. This rhythmic maturation of eggs and the other chemical and

physical events that accompany the process are called the menstrual cycle.

As a reaction to increasing levels of hormone FSH (follicle stimulating hormone), eggs start to

mature in a woman’s ovary. Each egg matures inside an egg sac, or follicle, near the surface of one

of the ovaries. When the egg is fully mature, another hormone – LH (luteinizing hormone) –

reaches peak level. As a reaction to these high hormone levels, the follicle bursts open and releases

the egg. This process is called ovulation. Tiny microscopic hairs, called cilia, on the cells at the

opening to the Fallopian tube or oviduct, sweep the egg into the tube which leads to the uterus.

As a reaction to increasing levels of the hormone estrogen, the lining of the uterus has been

prepared to receive a fertilized egg by building up its lining with nurturing tissues and blood

vessels.

After the egg is released from the follicle in the ovary, the remaining follicle tissue becomes a

hormone secreting gland, the corpus luteum. The gland releases the hormone progesterone. High

levels of progesterone help maintain the uterine

in its build up, nurturing phase.

If the released egg remains unfertilized, it

doesn’t implant into the uterus lining. This

triggers further hormonal changes. Both

estrogen levels and progesterone levels drop.

This causes the lining of the uterus to

deteriorate. As a result both unfertilized egg and

uterus lining are shed and pass out of the body.

This periodic loss of tissues and fluids from the

uterus is a normal function known as

menstruation. Menstruation is considered the

beginning of the monthly menstrual cycle.

All of these changes are governed by

coordinated hormones carried in the

bloodstream from their releasing gland to their

responding target cells. These hormones act through feedback mechanisms. The pituitary gland, at

the base of the brain, secretes the two hormones that trigger the growth and development of the

egg in the ovary – FSH and LH. In response, the ovary then secretes the two sex hormones that

control development of the egg and uterus lining – estrogen and progesterone. When ovarian

hormones reach low levels, this feedback mechanism stimulates the pituitary gland to once again

secrete its hormones to stimulate the development of another egg for another cycle.

Follicular Phase Study

Within the ovaries are located many egg cells. Each egg is enclosed within a structure called a

follicle. The follicle is aid to be immature. Under the influence of a hormone called FSH, the follicle

matures.

1. Prepare a line graph of the data in Table 1.

Table 1: FSH Levels measured over a Menstrual Cycle

Day 1 3 5 7 9 11 13 15 17 19 21 23 25 27

Units of FSH 10 12 14 13 13 14 20 10 9 9 8 8 8 10

2. FSH is a hormone in the female body that causes a woman’s follicles to mature within the

ovary. Using your graph, on which day of the cycle has the follicle reached maturity?

Day ____

3. What happens to the egg follicle in the ovary as FSH rises (during Days 1 – 12)?

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4. If the picture below is illustrating a cell secreting FSH, then draw what the receptors would

look like on the target cell in the ovary.

5. Describe the overall trend of FSH over a menstrual cycle.

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Luteal Phase

Once a follicle is mature, it bursts open and the egg is released. This process is called ovulation. The

egg passes into the oviduct where it may or may not become fertilized. Meanwhile, the mature

follicle, once it loses its egg, forms a body within the ovary called the corpus luteum.

A hormone called luteinizing hormone is responsible for ovulation. Table 2 shows data obtained

from blood samples taken from a female and analyzed for the amount of LH present.

1. What is the purpose of the corpus luteum?

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2. Describe how an egg goes from immature to a mature-released egg.

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3. Prepare a line graph of the data from Table 2.

Table 2: LH Levels measured over a Menstrual Cycle

Day 1 3 5 7 9 11 13 15 17 19 21 23 25 27

Units of LH 12 14 14 14 14 16 70 12 12 12 12 12 8 8

4. Luteinizing hormone stimulates the follicle in the ovary to release an egg. Using your graph,

on which day of the cycle will an egg be released? Day ____

5. What gland secrets LH? _____________________________

6. What happens to the egg in the ovary on Day 14 after LH levels reach their peak?

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7. If the picture below is illustrating a cell secreting LH, then draw what the receptors would

look like on the target cell in the uterus.

8. Describe the overall trend of LH over a menstrual cycle.

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Changes in the Uterus

While the follicular and luteal stages are taking place in the ovaries, a series of changes is also

occurring in the uterus. The uterus lining changes from being very thin to being very thick. This

change in thickness occurs because the number of cells increases through rapid cell division. At one

point, the uterus ceases to thicken. The buildup of cells begins to break apart. This breakdown of

the uterine lining, both as tissue loss and bleeding, is called menstruation.

Two hormones are responsible for the thickening of the uterus, estrogen and progesterone. The

amount of these hormones in the bloodstream influences the changes just described.

1. Prepare a line graph of the data from Table 3 on the next page.

Table 3: Amount of Estrogen and Progesterone Presence

Day of Cycle Units of Estrogen Present in Blood

Day of Cycle Units of

Progesterone Present in Blood

1 50 1 5

3 50 3 5

5 50 5 5

7 75 7 5

9 125 9 5

11 225 11 5

13 200 13 10

15 75 15 40

17 100 17 60

19 100 19 110

21 100 21 150

23 100 23 150

25 50 25 100

27 50 27 30

2. Based on the graph, when do estrogen and progesterone reach their peaks?

a. Estrogen ___

b. Progesterone ___

3. What gland secretes estrogen? __________________________

4. What happens to the uterus lining during days 1 – 12, as estrogen is rising?

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5. If the picture below is illustrating a cell secreting estrogen, then draw what the receptors

would look like on the target cell in the uterus.

6. Describe the overall trend of estrogen over a menstrual cycle.

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7. On day 14 the egg is released (ovulation). After that the corpus luteum forms in the

remaining follicle and it starts releasing progesterone. On what day does the progesterone

reach its peak concentration? ____

8. While progesterone stays at a high level what happens to the lining of the uterus?

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9. If the woman does not get pregnant, then the corpus luteum breaks down and the level of

progesterone starts declining. Once progesterone decreases what happens to the lining of

the uterus?

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Figure 1

Answer the following questions using Tables 1, 2, 3, Graphs 1, 2, 3, and Figure 1.

1. After a follicle has released an egg it turns into a corpus luteum. This in turn releases

estrogen and progesterone, which cause the uterine lining to thicken and prepare to receive

a fertilized egg. On which day would the uterine lining be the thickest? Day____

2. Look at the LH graph. How much time passes from the time the egg is released until when

the uterine lining is the thickest? ____ Days

3. What might account for this? (Hint: Where does egg start and where is the uterus?)

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4. If an egg is not fertilized, estrogen and progesterone levels ___________. When this occurs,

the thick lining of the uterus falls off and is released. This causes menstrual flow, or the

menstrual period. During which days in the cycle does menstruation occur? Days ____

5. If an egg is fertilized, it will attach to the thick __________________ wall and estrogen and

progesterone will continue to be released. What two things do these hormones prevent

from happening?

a. _____________________________________

b. _____________________________________

6. There are four stages/phases in a given menstrual cycle. Match these stages/phases with

the days below. Draw a line connecting the stages/phases and their corresponding days.

a. Follicular Phase (follicle is developing) ~Day 14

b. Ovulation (egg is released) ~Day 1-5

c. Luteal Phase (corpus luteum releases E and P) ~Day 15-28

d. Menstrual Period (excess uterine lining and egg released) ~Day 6-13

7. How might one trick the female body into thinking it was pregnant?

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8. After an egg implants on the thick uterine lining, the egg releases a hormone called hCG, or

human chorionic gonadotrophin (home pregnancy kits test for this hormone). What might

be the purpose of this hormone?

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9. Under which situations/conditions would the menstrual cycle stop?

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10. Why would the menstrual cycle stop during pregnancy?

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11. Is it possible to become pregnant during menstruation? Why or why not?

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12. If you miss your period, does that mean that you are pregnant? Explain.

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13. In Figure 1 Events in Lining of Uterus chart, what process is occurring between Days 3 – 6?

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14. Describe the changes that take place during the menstrual cycle from Day 5 – 13 to the

following:

a. Unfertilized egg in ovary ________________________________________________

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b. Uterus lining __________________________________________________________

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15. Describe what happens to the egg during the menstrual cycle on Day 14.

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16. Describe the changes that take place to the an egg:

a. From Day 15 – 28, if no fertilization occurs __________________________________

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b. From Day 15 – 21, if fertilization occurs ____________________________________

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c. From Day 21 – 26, if fertilization does occur _________________________________

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17. Explain why the female needs a thick uterus lining if fertilization does occur. ____________

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18. At what time during a woman’s menstrual cycle is it easiest to become pregnant?

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No Fertilization of Egg

Cut out individual boxes and place on the appropriate empty date on the accompanying calendar

labeled “Figure 2B Day by Day Changes in the Menstrual Cycle: No Fertilization of Egg”. Note: Do

not paste over the days with writing in them. Paste into the empty day next to the correct

description.

Fertilization of Egg

Cut out individual boxes and place on the appropriate empty date on the accompanying calendar

labeled, “Figure 3B Day by Day Changes in the Menstrual Cycle: Fertilization of Egg”. Note: Do not

paste over the days with writing in them. Paste into the empty day next to the correct description.