Name _______________________
LAB: Graphing the Human Menstrual
Cycle
Menstrual Cycle
When a human female is born, her ovaries already contain the primary oocytes that will
mature and produce eggs during her lifetime. Maturation of primary oocytes generally
begins between the ages of 12 and 14, when the female reaches sexual maturity. Most
commonly, eggs usually mature every 28 days or so, usually one at a time, in alternating
ovaries. The rhythmic maturation of eggs and the events that accompany the process are
termed the menstrual cycle.
Each egg matures inside an egg sac, or follicle, near the surface of one of the ovaries. When
the egg is fully mature, the follicle bursts. The egg is released in a process called ovulation.
Cilia sweep the egg into the Fallopian tube, which leads to the uterus. An unfertilized egg
will pass from the female’s body in a short time. The lining of the uterus, which has been
prepared for the arrival of an embryo, deteriorates and also passes out of the body. The
periodic loss of tissues and fluids from the uterus is a normal function known as
menstruation. A menstrual cycle is considered to begin at the onset of menstruation.
Hormones carried in the bloodstream bring about the changes in the menstrual cycle by
means of “feedback mechanisms.” The pituitary gland below the brain secretes hormones
that signal the growths and secretions in the ovary. Later, when the ovarian secretions reach
low levels, these low levels stimulate the pituitary gland to secrete more hormones, which
stimulate the development of another egg.
Problem: How do the levels of reproductive hormones influence the human menstrual
cycle?
Materials: Graph Paper, pencils, and the data table below
The relative hormone levels vary greatly during the menstrual cycle. The table below
shows the relative levels of the four major hormones by day.
Day
Luteinizing
Hormone (LH)
Follicle Stimulating
Hormone (FSH)
1
6
10
10
2
2
7
11
10
2
3
8
12
10
2
4
8
13
10
2
5
8
14
10
2
6
8
13
13
2
7
8
12
16
2
8
8
12
19
2
9
8
12
22
2
10
10
13
28
2
11
12
14
35
2
12
22
16
28
3
13
32
20
22
4
14
20
15
19
5
15
6
10
16
8
16
6
9
15
10
17
6
8
15
12
18
6
8
15
15
19
6
8
15
18
20
6
7
15
24
21
6
6
15
28
22
6
6
15
28
23
6
6
15
28
24
5
6
13
24
25
4
6
10
18
26
3
8
10
12
27
3
10
10
7
28
3
10
10
2
Estrogen Progesterone
Procedure:
Graphing
 Plot the data points and then draw a line graphs in "connect-the-dot" fashion.
 Do two different graphs.
o Plot estrogen and progesterone on one of the graphs.
o Plot FSH and LH on the other graph.
 Make certain you key each graph, label the axes, and title your graphs.
Conclusion Questions Answer the questions which follow using your knowledge of the
menstrual cycle and your information on the graph you will construct.
1. On which day are estrogen levels highest?
2. On which day are LH levels the highest?
3. How does the increase in the estrogen level correspond to the thickness of the
uterine lining (endometrium)? Explain why this makes sense based on the function
of estrogen.
4. What happens to the thickness of the uterine lining when the level of the hormone
progesterone reaches its highest levels? Why does this make sense based on the
function of progesterone?
5. List an event the hormone LH appears to trigger based on the rapid occurrence of
these events soon after it reaches its highest level.
6. Why is it logical for the level of FSH to fall greatly following ovulation?
7. Explain why it makes sense that the levels of estrogen and progesterone are low
in the blood of a female during menstruation. (Keep in mind the uterine lining is shed
at this time.)
8-11. State the role in the menstrual cycle of the following hormones; FSH, LH,
estrogen, and progesterone.
12-13. Complete the following chart.
Menstrual Cycle Stage
1. ____________________________
Major Event(s) of Stage
-- production of ova
occurs in tiny cavities in
the ovary called
_________________
-- enlarging follicle
produces estrogen which
causes the uterus to get
ready for embryo
implantation (thickens
its lining)
2. Ovulation
3. ________________________________
4. ________________________________
-- yellow tissue fills the
follicle after ovulation
-- called the
____________________
"yellow body" -secretes the hormone
__________________
which maintains the
thickness of the uterine
lining, thus readying the
uterus for pregnancy
-- periodic shedding of
the thickened lining of
the uterus which occurs
if fertilization does not
occur