Science
Quarter 3 - Module 2
Feedback Mechanisms in the
Female Reproductive System
Department of Education ● Republic of the Philippines
10
Science- Grade 10
Alternative Delivery Mode
Quarter 3 – Module 2: Feedback Mechanisms in the Female Reproductive System
First Edition, 2020
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Co-Chairpersons
Members
:
:
:
:
:
Crystal Jade S. Mongas
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Ellen A. Azuelo, PhD, Rejynne Mary L. Ruiz, PhD
Crystal Jade S. Mongas
: Arturo B. Bayocot, PhD, CESO III
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: Victor G. De Gracia Jr., PhD, CESO V
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: Randolph B. Tortola, PhD, CESO IV
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Lesson 1
The Menstrual Cycle
What’s New
WHAT’S THE WORD?
Direction: Observe the four pictures and solve the puzzle by working out what the word is.
Every box corresponds to a certain letter. Write your answer in a separate sheet
of paper.
Figure 1.1 What’s the word model
Source: www.google.com Images Labeled for Reuse
This process only occurs among females. It is a normal vaginal bleeding that occurs as part of a
female’s monthly cycle which is known as menstruation.
What Is It
We have previously discussed that an ovary normally releases only one egg every 28
days. What controls the timing are the hormones. Hormones control many of the changes in
the reproductive system. They also coordinate the development of the ovum and the uterus.
Remember that hormones are chemicals that can affect certain body organs. This cycle
among females occurs every month starting when a female is 10 to 13 years old and it
continues for about 40 years. If an ovum is not fertilized in the fallopian tube, the corpus
luteum degenerates, the progesterone production stops, and the inside membrane of the
uterus breaks down. The breakdown and discharge of the soft uterine tissues and the
fertilized egg is called menstruation. This is the monthly changes or periods that take place
in the female reproductive system.
3
1
The Menstrual Cycle
The female sex hormones control the secondary sex characteristics as well as the
ovarian and uterine cycle. Like males, females also secrete follicle stimulating hormone
(FSH) and luteinizing hormone (LH) as directed by the pituitary gland during puberty. This
signals the start of puberty which includes the development of the secondary sex
characteristics in females and the onset of menstruation. A female experiences body
changes even before the first menstruation which is also known as menarche. The female
secondary sex characteristics include the development of the breast; growth of underarm
and pubic hair; rounded body shapes brought about by a widespread layer of fat in areas like
the abdomen, hips and thighs; widening of the hips in preparation for childbirth; and the
development of higher pitched voice. At puberty, the master gland which is the pituitary
gland starts a series of hormonal changes that make a woman capable of pregnancy. These
hormonal changes and the effects they produce is called the menstrual cycle. While the
length of this cycle varies, the typical cycle is about 28 days. During this process, changes in
both the ovary and the uterus take place.
The Ovarian Cycle
At the start of the cycle, the pituitary gland secretes increased amount of FSH and
this allows an ovarian follicle to mature. The female sex hormone called estrogen, is also
secreted as the follicle cells develop. When the follicle cells multiply, the cells signal an
increased level of estrogen in the blood, and the pituitary gland secretes another hormone,
the luteinizing hormone (LH).
LH and FSH
bring
about
the
maturation
of
the
follicle which results to
ovulation
-the
releasing of the mature
egg. Ovulation usually
occurs on the 14th day
of the cycle. During
ovulation, the egg is
ready for fertilization
within 24 hours from its
release. Still under the
influence of LH, the
cells of the ruptured
follicle develop into a Figure 1.2 The ovary (Source: www.google.com Labeled for Reuse)
yellow body called the
corpus luteum. The yellow body then produces more estrogen and another female sex
hormone called the progesterone. Both hormones prepare the uterine wall for the possible
implantation of a fertilized egg. The rise in the level of estrogen and progesterone exerts a
feedback control over the pituitary gland to inhibit the secretion of LH and FSH. The corpus
luteum is deprived of the hormones that maintain it with the drop in the amount of these two
hormones, hence the corpus luteum begins to degenerate. Thus, the gland’s influence on
the progesterone level will affect the endometrial wall in a domino effect.
The Uterine Cycle
A series of changes also happens in the uterus as a consequence of the hormones
while events are taking place in the female’s ovary. With the low levels of progesterone, the
surface of the endometrium or wall begins to disintegrate and the blood vessels rupture.
Blood and some accompanying endometrial tissues flow out of the vagina in a process
called menstruation. This menstrual phase lasts for about five days.
24
The Uterine Cycle
A
series
of
changes also
happens in
the uterus as
a
consequence
of
the
hormones
while events
are
taking
place in the
female’s
ovary. With
the low levels Figure 1.3 The ovarian and uterine cycle(Source: www.google.com Labeled for Reuse)
of
progesterone, the surface of the endometrium or wall begins to disintegrate and the blood
vessels rupture. Blood and some accompanying endometrial tissues flow out of the vagina in
a process called menstruation. This menstrual phase lasts for about five days.
After the menstrual period, the endometrium starts to build up due to the increasing
amount of estrogen by the developing follicles in the ovary. This is the proliferative phase of
the uterine cycle which lasts for 6 to 14 days. The formation of the corpus luteum and the
secretion of progesterone trigger the endometrium to double in thickness and prepare itself
for a developing embryo. The uterine glands also become mature and they produce a thick
secretion. Hence, the secretory phase of the uterine cycle begins on the 15 th day until before
the onset of the next menstrual phase. However, this cycle may be interrupted by stress,
health concerns and pregnancy. But if pregnancy does not occur, the cycle begins anew.
What’s More
ACTIVITY: CAN YOU DESCRIBE ME?
In this activity, you will describe how menstruation occurs in the female reproductive system.
Direction: Study the diagram below to describe how menstruation occurs and answer the
guide questions that follow.
Figure 1.4 The phases/cycles (Source: www.google.com Labeled for Reuse)
35
Guide Questions
1. Record your observations on the table below.
Phases
Hormones Involved
2. How does the menstrual cycle occur in females?
_____________________________________________________________
_____________________________________________________________
Remember, hormones coordinate the development of the ovum and the uterus.
Lesson 2
Hormone Feedback and
Menstruation
What’s New
Menarche is the most obvious signal of the onset of puberty in females. This is
the first menstrual discharge of
blood
from
the
vagina.
Menarche also signals the
beginning of cyclic changes in
the ovary.
Oocytes
that
were
unripe or untouched are now
brought up to become active.
Thus, every month, an ovarian
cycle takes place. Figure 2.1
shows the changes in the lining
of the uterus as the month
progresses.
Before moving on, let us
Figure 2.1 Changes in the uterine lining
first try an activity. In this
(Source: www.google.com Labeled for Reuse)
activity, you are expected to
compare the changes that occur during the menstrual cycle. Try to figure out what
occurs in its every stage.
Direction: Complete the table below by comparing the changes that occur during the
menstrual cycle.
Part
Event
Blood Flow
Follicular
Ovulation
Luteal
Menstruation occurs.
The follicles are formed in the ovary.
The oocytes burst from the ovary.
The corpus luteum is formed.
46
Number of
Days
5
Hormone
Produced
What Is It
The human ovaries
can usually produce only one
egg during a 28-day cycle of
activity. The mass of ovarian
cells produces an ovum or an
egg and it also forms a
follicle. The cycle is controlled
by FSH or the FollicleStimulating Hormone. This
hormone is produced in the
anterior lobe of the pituitary
gland. The follicle becomes
filled with a fluid containing
the hormone estrogen when
the egg reaches maturity.
Figure 2.2 A cross section of the ovary
Most importantly, the rising
level of FSH stimulates follicle maturation and estrogen production.
Figure 2.2 shows the cross section of a human ovary with different stages of
development. As the cycle continues and after the ovum has been discharged, the follicle
turns yellow and it forms the corpus luteum. The yellow body formation is controlled by
another hormone of the pituitary gland called the LH or luteinizing hormone. The corpus
luteum then produces another hormone known as progesterone. Progesterone brings about
effects in the secondary characteristics primarily on the breasts. During pregnancy,
progesterone causes breast enlargement. Moreover, this hormone maintains the growth of
the mucus lining of the uterus.
To summarize, the important female hormones are as follows:
Female
Hormone
Estrogen
Location
Follicles/Ovary
Progesterone
Corpus Luteum/Ovary
LH
Pituitary Gland
FSH
Pituitary Gland
Function
Responsible for secondary female
characteristics; thickens endometrium; inhibits
growth of facial hair
Stimulates endometrium; inhibits uterine
contractions and ovulation
Develops and maintains the corpus luteum;
stimulates ovulation
Stimulates the formation of follicles in the
ovaries
Have you experienced menstrual cramps? Probably yes, you have. In reality, some
females experience menstrual cramps every month. Did you know that menstrual cramps
are the results of the strong contractions of the uterine wall that occur before and during
menstruation? What do you think is its cause?
Cramps can be caused by the excessive secretion of prostaglandins. Shedding of
the endometrium of the uterus results in the inflammation of the endometrial layer. As a
consequence of this inflammation, prostaglandins are produced.
In a nutshell, the following summarizes the important events during the menstrual
cycle:
1. The pituitary gland begins the cycle.
2. The pituitary releases hormones that cause the egg in the ovary to mature.
The luteinizing hormone (LH) initiates the maturation of the follicles, converts
ruptured follicle into the corpus luteum and cause the secretion of
75
progesterone. The other hormone, follicle stimulating hormone (FSH)
assists in the maturation of the follicles and cause the secretion of estrogen
from the follicles.
3. Meanwhile, the ovary itself releases a hormone called estrogen. Estrogen is a
hormone that causes changes in the female reproductive system. This
hormone also causes the uterus to increase in thickness. The uterus becomes
thicker so that the fertilized egg can attach to it.
4.
5.
6.
7.
8.
The ovary releases an egg on day 14. Now, assume that no sperm was present.
The egg moves through the oviduct and enters the uterus.
At the same time, the uterus continues to thicken.
The egg has not been fertilized, therefore, it will not attach to the uterus.
The thick uterus is no longer necessary, so it begins to break apart. The cells of
the thickened uterus break off and leave the vagina. The unfertilized egg is also
lost. Some blood is lost, too. This loss of cells from the uterus lining, blood and
egg is called menstruation.
9. After menstruation, the cycle starts again.
What is a feedback mechanism?
A
feedback
mechanism is the process
through which the level of a
certain substance influences
the
level
of
another
substance.
A
negative
feedback
affects
the
production of hormones in
the
menstrual
cycle.
Moreover, high levels of one
hormone may inhibit the
production
of
another
hormone. Figure 2.3 presents
the
negative
feedback
mechanisms in the menstrual
cycle. Based on the figure,
Figure 2.3 Negative feedback mechanisms in the menstrual cycle
follicle stimulating hormone or
FSH stimulates the ovaries to
release estrogen. High levels of estrogen then prevent more production of FSH.
Estrogen then stimulates the release of luteinizing hormone or LH from the pituitary
gland, which in turn, controls the production of progesterone. Moreover, high levels of
progesterone can then inhibit the further release of LH.
86
What’s More
ACTIVITY 1: CAN YOU JUSTIFY ME?
Objective
Determine the hormones involved in regulating the processes in the female
reproductive system
Procedure
Check “Yes” if the hormone is involved in regulating the given process, otherwise
check “No”. If your answer is “No”, please state the reason behind it. Write your
answers in the table.
Hormone
Yes
No
Reason
1. Adrenocorticotropic
2. Estrogen
3. Antidiuretic Hormone
4. Progesterone
5. Parathyroid Hormone
6. Luteinizing Hormone
7. Epinephrine
8. Follicle Stimulating Hormone
9. Testosterone
10. Melatonin
Activity 2
A. Study the given pictures to describe the feedback mechanisms involved during the
menstrual cycle and answer briefly the guide questions below.
A
B
Source: www.google.com Images Labeled for Reuse
9
97
Guide Questions
1. How long does a menstrual cycle usually last if fertilization has not taken place?
2. Describe what happens to the egg during the first 14 days of the cycle in Part B.
3. Describe what happens to the egg and the uterus during the last 14 days of the
cycle in Part A.
4. What takes place after fertilization?
Hormone Feedback and
Pregnancy
Lesson 3
What’s New
Now that you have already known about the parts and functions of the human
reproductive system, let us now trace what happens to the ovulated egg to its orderly
sequence of events from the time an egg is ovulated. In this activity, you should be able to
arrange the sequence from the beginning to the end of fertilization and implantation in the
uterus.
Direction: Complete the table below by sequencing the events from the time an egg is
ovulated. Arrange orderly by numbering the items from 1 to 7. Write your answer
inside the table.
Event
Sequence
Fertilized egg attaches to the uterus
Fertilized egg moves out of the oviduct
Egg is fertilized in the oviduct
Vagina receives the sperm
Egg moves into the oviduct
Egg is released from the ovary
Egg is in the ovary
What Is It
A zygote or a fertilized egg is formed when a
sperm successfully penetrates the nuclei fuse. A
fertilization membrane develops to prevent other
sperms to further penetrate the egg. This process
wherein the sperms’ nucleus and the ovum’s unite is
called fertilization. It usually takes place while the egg
is traveling along the oviduct or fallopian tube. It will
take about 7 to 10 days for an egg, fertilized or not, to
reach the uterus.
Figure 3.1 The zygote
Source: www.google.com Image Labeled for Reuse
108
Upon successful implantation of a developing embryo in the endometrium, the
developing embryo and the uterine lining jointly form a special organ called the placenta.
This will provide nourishment for the embryo. It also secretes the hormone called human
chorionic gonadotropin (HCG), which is related to LH since they act on the same receptor.
Remember that the LH maintains the corpus luteum. With the corpus luteum intact,
progesterone production is maintained and the uterine wall will not menstruate. HCG actually
passes in the urine. It is the
same hormone detected in
pregnancy tests. If the embryo is
abnormal or if it dies, HCG will
drop and the endometrium will
disintegrate causing a woman to
have a miscarriage.
As your guide, refer below for the
summary of the stages of
reproduction:
Figure 3.2 Pregnancy test
Source: www.google.com Image Labeled for Reuse
1. Egg cells are formed in each ovary.
2. Each month, one ovary releases an egg.
Normally, only one egg is released about
every 28 days. The ovaries usually take turns in releasing the eggs.
3. Once released from the ovary, the egg moves into a tube called oviduct.
Oviducts are tube-like organs that connect the ovaries to the uterus. The uterus
is a muscular organ in which the fertilized egg develops.
4. Sperm cells are released into the vagina during mating. The vagina is a
muscular tube that leads from the outside of the female’s body to the uterus.
Sperm cells swim from the vagina into the uterus and into the oviducts. If an
egg is present, fertilization takes place. Once fertilized, the egg moves down the
oviduct into the uterus.
5. The fertilized egg then attaches itself
into the wall of the uterus which is called
implantation. Once attached, it will
remain there for nine months as it
develops into a baby.
Figure 3.3 A human embryo
Source: www.google.com Image Labeled for Reuse
What
is
ectopic
pregnancy? Ectopic pregnancy
results if implantation occurs
anywhere other than the uterine
cavity. The most common site of
ectopic pregnancy is in the
fallopian tube. Implantation in the
fallopian tube can be fatal and can
cause the tube to rupture. In
some cases, implantation can
occur in the mesenteries of the
abdominal cavity and the fetus
can develop normally, but must be
delivered by caesarian section.
Figure 3.4 A cross section of the ovary
Source: www.google.com Image Labeled for Reuse
119
As a summary, outlined below are the different processes involved during pregnancy.
Ovulation
This refers to the release of a mature egg from the ovary. It usually takes
place on the 14th day from the first day of menstruation if the cycle is a 28-day cycle.
Fertilization
When a sperm encounters an egg cell in the fallopian tube, it releases digestive
enzymes. Those enzymes clear the path for the sperm nucleus to fuse with the
nucleus of the ovum or egg cell. A zygote is now formed.
Implantation
This occurs before the end of the first week. By this process, the zygote
attaches to the uterine lining, and some of its cells send out projections that has been
part of the maternal tissue. The inner cell mass becomes the embryonic disc. This disc
will give rise to the embryo proper during the week following implantation.
Birth or Parturition
“Happy birthday!” is a very common greeting to mark the anniversary of a person’s
birth.
Birth takes place about 39 weeks after fertilization. The birth process begins when
the uterus starts to contract. For the next two to eighteen hours, the contraction becomes
stronger and more frequent. The cervical canal dilates fully and the amniotic sac ruptures.
Birth typically occurs less than an hour after full dilation. Immediately afterward,
uterine contraction forces fluid, blood and the placenta out of the body. The umbilical cord
is now cut, and the newborn embarks on its nurtured existence in the outside world.
What’s More
ACTIVITY: A-MAZE-ING EGG RACE!
Objective Trace the processes involved during the release of an egg and fertilization
Procedure
Shade the arrow that correctly traces the processes involved during the release of an
egg. Your answers will guide you to the end of the maze.
12
10
Assessment (Unit Test)
Direction: Choose the CAPITAL LETTER of the best answer. Write the chosen letter on a
separate sheet of paper.
1. Which days of the cycle does menstruation occur?
A. days 1-6
B. days 7-13
C. days 14-20
D. days 21-28
2. A biologist made a hypothesis that the pituitary and the ovary both influence the uterine
cycle in females, which of the following observation would best support this hypothesis?
A. The removal of pituitary is followed by death.
B. The removal of the ovary can greatly affect the menstrual cycle.
C. The removal of the ovary is followed by a non-functioning pituitary.
D. The uterine development takes place only when both pituitary and ovary are present.
3. A woman’s unsafe period is the day near or during _________.
A. fertilization
B. menstruation
C. ovulation
D. sexual intercourse
4. In a typical 28-day menstrual cycle, on which day following the beginning of the menstrual
period is the level of luteinizing hormone most likely to be the highest?
A. day 7
B. day 14
C. day 21
D. day 28
5. What happens during ovulation?
A. A sperm can fertilize an egg.
B. A zygote becomes an embryo.
C. An ovum is released from the ovary.
D. A follicle releases the hormone FSH.
6. It is the process through which the level of a certain substance influences the level of
another substance?
A. FSH
B. LH
C. menstruation
D. feedback
7. An increase in FSH may also indicate a reduction in the production of good quality eggs
and embryos for _________.
A. fertilization
B. menstruation
C. ovulation
D. all of the choices
8. It is an abnormally high levels of LH during non-ovulatory times in the menstrual cycle.
A. menarche
B. menopause
C. LH
D. FSH
9. What signals the beginning of cyclic changes in the ovary?
A. menarche
B. menopause
C. LH
D. FSH
10. Which of the following is produced by the mass of ovarian cells?
A. sperm
B. ovum
C. LH
D. FSH
11. Where are the sperm cells released during mating?
A. ovaries
B. uterus
C. fallopian tube
D. vagina
12. What does the ovary release every month?
A. egg
B. sperm
C. LH
D. FSH
13. If the embryo is abnormal or if it dies, _______ will drop.
A. HCG
B. LH
C. FSH
D. all of the choices
14. What results to the disintegration of the endometrium?
A. menarche
B. menopause
C. menstruation
D. miscarriage
15. Which of the following is the most common site of ectopic pregnancy?
A. ovaries
B. fallopian tube
C. uterus
D. vagina
13
11
Answer Key
Lesson 1
What’s New
MENSTRUATION
What’s More
ACTIVITY: CAN YOU DESCRIBE ME?
1. Follicular Phase - Estrogen
Luteal Phase - Estrogen and Progesterone
2. The egg travels through a thin tube called fallopian tube. If the egg is fertilized by a sperm it attaches itself
to the wall of the uterus, where over time, develops into a baby. If the egg is not fertilized, the uterus lining
breaks down and bleeds causing menstrual flow.
Lesson 2
What’s New
1. Blood flow – none
2. Follicular – Estrogen
3. Ovulation – None
4. Luteal – Estrogen and Progesterone
What’s More
ACTIVITY 1: CAN YOU JUSTIFY ME?
1. No – synthesis of sex steroids
2. Yes
3. No – increase water absorption
4. Yes
5. No – stimulates calcium uptake
6. Yes
7. No – increases heart rate and blood sugar
8. Yes
9. No – male development
10. No- blocks secretion of LH and FSH, promotes sleep
Activity 2
1. 28 days
2. It moves out of the uterus
3. The egg is fertilized and attaches to the uterus for implantation.
4. Implantation
Lesson 3
What’s New
What’s More
ACTIVITY: A-MAZE-ING EGG RACE!
Assessment
1. D
11. D
2. B
12. A
3. C
13. A
4. B
14. D
5. A
15. B
6. D
7. A
14
12
8. B
9. A
10. B