Reproduction: Topics 6.6 and 11.4

6.6.1 Draw and label diagrams of the adult male and female reproductive systems.

Male Reproductive System

Female Reproductive System

6.6.2 Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating hormone), LH (luteinizing hormone), estrogen and progesterone.

The Menstrual Cycle

1. FSH is secreted by the pituitary gland and its levels start to rise. This stimulates the follicle to develop and

the follicle cells to secret estrogen. 

2. Estrogen then causes the follicle cells to make more FSH receptors so that these can respond more

strongly to the FSH. 

3. This is positive feedback and causes the estrogen levels to increase and stimulate the thickening of the

endometrium (uterus lining). 

4. Estrogen levels increase to a peak and by doing so it stimulates LH secretion from the pituitary gland. 

5. LH then increases to its peak and causes ovulation (release of egg from the follicle). 

6. LH then stimulates the follicle cells to secrete less estrogen and more progesterone. Once ovulation has

occurred, LH stimulated the follicle to develop into the corpus luteum. 

7. The corpus luteum then starts to secrete high amounts of progesterone. This prepares the uterine lining

for an embryo. 

8. The high levels of estrogen and progesterone then start to inhibit FSH and LH. 

9. If no embryo develops the levels of estrogen and progesterone fall. This stimulates menstruation (break

down of the uterine lining). When the levels of these two hormones are low enough FSH and LH start to

be secreted again.

10. FSH levels rise once again and a new menstrual cycle begins.

6.6.3 Annotate a graph showing hormone levels in the menstrual cycle, illustrating the relationship between changes in hormone levels and ovulation, menstruation and thickening of the endometrium.

6.6.4 List three roles of testosterone in males.

1. Stimulates the development of prenatal genitalia.

2. Stimulates the development of the male secondary sexual characteristics such as growth of the skeletal

muscle and pubic hair. 

3. During adulthood it maintains the sex drive.

6.6.5 Outline the process of in vitro fertilization (IVF).

1. For a period of three weeks, the woman has to have a drug injected to stop her normal menstrual cycle. 

2. After these three weeks, high doses of FSH are injected once a day for 10-12 days so that many follicles

develop in the ovaries of the women. 

3. HCG (another hormone) is injected 36 hours before the collection of the eggs. HCG loosens the eggs in the

follicles and makes them mature. 

4. The man needs to ejaculate into a jar so that sperm can be collected from the semen. The sperm are

processed to concentrate the healthiest ones. 

5. A device that is inserted through the wall of the vagina is used to extract the eggs from the follicles. 

6. Each egg is then mixed with sperm in a shallow dish. The dishes are then put into an incubator overnight. 

7. The next day the dishes are looked at to see if fertilization has happened. 

8. If fertilization has been successful, two or three of the embryos are chosen to be placed in the uterus by

the use of a long plastic tube.

9. A pregnancy test is done a few weeks later to find out if any of the embryos have implanted.

10. A scan is done a few weeks later to find out if the pregnancy is progressing normally.

6.6.6 Discuss the ethical issues associated with IVF.

Arguments for IVF Arguments against IVF

Many types of infertility are due to environmental factors rather than genetic which means that the offspring would not inherit the infertility.

The infertility of the parents may be inherited by their offspring passing on the suffering to the next generation.

The embryos that are killed during the IVF process cannot feel pain or suffering as they do not have a developed nervous system.

More embryos are produced than needed and the ones that remain are usually killed which denies them the chance of a life.

Suffering caused by genetic diseases can be decreases by screening the embryos before placing them into the uterus.

Embryologists select which embryos will be placed into the uterus. Therefore they decide the fate of new individuals as they choose which ones will survive and which ones will die.

Since the IVF process is not an easy one emotionally and physically, is costly, takes time and there are no guarantees, parents who are willing to go through it must have a strong desire to have children and therefore are likely to be loving parents.

IVF is not a natural process which takes place in a laboratory compared to natural conception which occurs as a result of an act of love.

Infertility can cause emotional suffering to couples who want to have children. IVF can take away this suffering for some of those couples.

Infertility should be accepted as God’s will and to go against it by using IVF procedures would be wrong.

11.4.1 Annotate a light micrograph of testis tissue to show the location and function of interstitial cells (Leydig cells), germline epithelium cells, developing spermatozoa and Sertoli cells.

Testis Tissue

The testes are composed of seminiferous tubules which produce sperm

Each tubule is surrounded by a basement membrane which is lined by germline epithelium cells

The germline epithelium will divide by mitosis to make spermatogonia (which divide by meiosis to make

spermatozoa)

The developing spermatozoa are nourished by Sertoli cells

Outside of the tubules are blood capillaries and interstitial cells (Leydig cells), which produce the male sex

hormone, testosterone 

11.4.2 Outline the processes involved in spermatogenesis within the testes, including mitosis, cell growth, the two divisions of meiosis and cell differentiation

Spermatogenesis Spermatogenesis describes the production of

spermatozoa (sperm) in the seminiferous tubules

of the testes

The first stage of sperm production requires the

division of germline epithelium by mitosis

These cells (spermatogonia) then undergo a period

of growth

This is followed by two meiotic divisions that result

in four haploid daughter cells

These haploid cells then differentiate to form

sperm cells

The developing sperm cells are nourished

throughout by the Sertoli cells

11.4.3 State the role of LH, testosterone and FSH in spermatogenesis

LH:  Stimulates the interstitial cells (Leydig cells) to produce testosterone

FSH:  Stimulates the (first) meiotic division of spermatogonia

Testosterone:  Stimulates the (second) meiotic division of spermatogonia and the maturation of spermatozoa

through differentiation

11.4.4 Annotate a diagram of the ovary to show the location and function of germline epithelium, primordial follicles, mature follicles and secondary oocyte

Structure of the Ovary

The ovary contains follicles in various stages of development

Egg cells within primordial follicles have been arrested in prophase I and have yet to undergo meiotic division

Egg cells within mature follicles have begun meiotic division and are released from the ovary as secondary

oocytes (arrested in prophase II)

The ruptured follicle develops into a corpus luteum that will, in time, degenerate into a corpus albicans

The germline epithelium functions as an epithelial layer separating ovarian tissue from the rest of the body - it is

not involved in oocyte development

11.4.5 Outline the processes involved in oogenesis within the ovary, including mitosis, cell growth, the two divisions of meiosis, the unequal division of cytoplasm and the degeneration of polar body

Oogenesis Oogenesis describes the production of female

gametes (ova) within the ovary

The process begins during fetal development, when

a large number of cells (oogonia) are formed by

mitosis before undergoing a period of growth

These cells begin meiosis but are arrested in

prophase I until puberty

At puberty, some follicles continue to develop each

month is response to FSH secretion

These follicles complete the first meiotic division to

form two cells of unequal size

The cell with less cytoplasm is a polar body (which

degenerates), while the larger cell forms a

secondary oocyte

The secondary oocyte begins the second meiotic

division but is arrested in prophase II (until

fertilization) It is released from the ovary (ruptured follicle

develops into corpus luteum) and, if fertilization

occurs, will complete meiosis

The second meiotic division will produce an ovum

and a second polar body

11.4.6 Draw and label a diagram of a mature sperm and egg

11.4.7 Outline the role of the epididymis, seminal vesicle and prostate gland in the production of semen

Epididymis

Testicular fluids are removed, concentrating the sperm

Sperm mature and develop the ability to swim

Seminal Vesicle

Adds nutrients (including fructose) for respiration

Secretes prostaglandins, causing contractions to the female system and helping sperm move towards the egg

Prostate Gland

Secretes alkaline fluid which neutralizes vaginal acids (changes pH from 4 to 6 which aids sperm motility)

11.4.8 Compare the processes of spermatogenesis and oogenesis, including the number of gametes and the timing of formation and release of gametes

Similarities:

Both processes result in the formation of haploid gametes

Both processes involve mitosis, growth and meiosis

Differences:

11.4.9 Describe the process of fertilization, including the acrosome reaction, penetration of the egg membrane by a sperm and the cortical reaction

When the sperm enters the female reproductive tract, biochemical changes to the sperm occur in the final part

of its maturation (capacitation) 

The sperm is attracted to the egg due to the release of chemical signals from the secondary oocyte (chemotaxis)

Fertilization generally occurs in the oviduct (fallopian tube)

To enter the egg membrane, the sperm must penetrate the protective jelly coat (zona pellucida) surrounding the

egg via the acrosome reaction

The acrosome vesicle fuses with the jelly coat and releases digestive enzymes which soften the glycoprotein

matrix

The membrane of the egg and sperm then fuse and the sperm nucleus (and centriole) enters the egg

To prevent other sperm from penetrating the fertilized egg (polyspermy), the jelly coat undergoes biochemical

changes via the cortical reaction

The cortical granules release enzymes that destroy the sperm-binding proteins on the jelly coat

Now fertilized, the nucleus of the secondary oocyte completes meiosis II and then the egg and sperm nuclei fuse

to form a diploid zygote

11.4.10 Outline the role of hCG in early pregnancy

The endometrium is a blood-rich environment in which an implanted zygote can grow and it is sustained by the

hormone progesterone

If progesterone levels aren't maintained (i.e. the corpus luteum degenerates), then the endometrium will be

sloughed away (menstruation)

A fertilised zygote develops into a blastocyst that secretes human chorionic gonadotrophin (hCG)

hCG maintains the corpus luteum post-ovulation so that the blastocyst can remain embedded in the

endometrium and continue to develop

Gradually the placenta develops and produces progesterone (at around 8 - 10 weeks), at which point the corpus

luteum is no longer needed

Role of hCG in Early Pregnancy

11.4.11 Outline early embryo development up to the implantation of the blastocyst

After fertilization, the zygote undergoes several mitotic divisions to create a solid ball of cells called a morula (at

around 4 days)

Unequal divisions beyond this stage cause a fluid-filled cavity to form in the middle - this makes a blastocyst (at

around 5 days)

The blastocyst consists of:

An inner mass of cells (this will develop into the embryo)

An outer layer called the trophoblast (this will develop into the placenta)

A fluid filled cavity (called the blastocoele)

These developments all occur as the developing embryo is moving from the oviduct to the uterus

When the blastocyst reaches the uterus, it will embed in the endometrium (implantation)

Early Embryo Development

11.4.12 Explain how the structure and function of the placenta, including its hormonal role in secretion of estrogen and progesterone, in maintaining pregnancy

Structure and Function The placenta is a disc-shaped structure that nourishes the developing embryo

It is formed from the development of the trophoblast upon implantation and eventually invades the uterine wall

The umbilical cord connects the fetus to the placenta and maternal blood pools via open ended arterioles into

intervillous spaces (lacunae)

Chorionic villi extend into these spaces and facilitate the exchange of materials between the maternal blood and

fetal capillaries

Nutrients, oxygen and antibodies will be taken up by the fetus, while carbon dioxide and waste products will be

removed

The placenta is expelled from the uterus after childbirth

Hormonal Role The placenta also takes over the hormonal role of the ovary (at around 12 weeks)

Estrogen stimulates growth of the muscles of the uterus (myometrium) and the development of the mammary

glands

Progesterone maintains the endometrium, as well as reduces uterine contractions and maternal immune

response (no antibodies against fetus)

Both estrogen and progesterone levels drop near time of birth

Structure of the Placenta

11.4.13 State that the fetus is supported and protected by the amniotic sac and amniotic fluid

The fetus develops in a fluid-filled space called the amniotic sac

Amniotic fluid is largely incompressible and good at absorbing pressure, and so protects the child from impacts

to the uterine wall

The fluid also creates buoyancy so that the fetus does not have to support its own body weight while the skeletal

system develops

Finally, amniotic fluid prevents dehydration of the tissues, while the amniotic sac provides an effective barrier

against infection

11.4.14 State that materials are exchanged between the maternal and fetal blood in the placenta

The fetus relies on the exchange of materials across the placental wall to grow and develop:

11.4.15 Outline the process of birth and its hormonal control, including the changes in progesterone and oxytocin levels and positive feedback

The process of childbirth is called parturition and is controlled by the hormone oxytocin

After nine months, the fetus is fully grown and takes up all available space in the uterus, stretching the walls of

the uterus

This causes a signal to be sent to the brain, releasing oxytocin from the posterior pituitary

Oxytocin inhibits progesterone, which was inhibiting uterine contractions

Oxytocin also directly stimulates the smooth muscle of the uterine wall to contract, initiating the birthing

process

The contraction of the uterine wall causes further stretching, which triggers more oxytocin to be released

(causing even more contraction)

Additionally, the fetus responds to the cramped conditions by releasing prostaglandins which cause further

myometrial contractions

As the stimulus causing oxytocin release is increased by the effects of oxytocin, this creates a positive feedback

pathway

Contractions will stop when labor is complete and the baby is birthed (no more stretching of the uterine wall)

The Hormonal Control of Child Birth