ReproductionReproduction6.6 and 11.4

Male Anatomy

Alternate View

Male Hormones Fun Fact: Men can be fertile until 94

years! Testasterone

› Determines the development of male gentalia during embryonic development

› Ensures the development of secondary sex characteristics during puberty

› Maintains the sex drive of males throughout their lifetime

Testes Tissue

The seminferous tubule is where the sperm cells are produced.

Testes Tissue Leydig/Interstitial Cells: produce the

male sex hormone, testosterone Germanal Epithelium Cells: will divide

by mitosis to make spermatagonia Developing Spermazoa: carrier of

gentic material in the formation of zygotes

Sertoli Cells: will provide the spermazoa with nutrients for development

Spermatogenesis

Spermatogenesis Cells in germinal epithelium divide by

mitosis These cells are pushed toward the center of

the seminiferous tubes, then grow Divide by meiosis to form two haploid cells Another division occurs in each haploid cell Thus four cells are produced and attach to a

Sertoli cell where they are nourished

Hormones in Spermatogenesis

Leutinizing Hormone (LH): stimulates Leydig cells to produce testosterone

Follicle Stimulating Hormone (FSH) and Testaterone: stimulate the meiotic divisions of spermatagonia into spermatazoa

Mature Sperm

Fun Fact: the average male ejaculates between 2 and 5mL of semen and there are anywhere between 50 and 130 million sperm in each milliliter.

Sperm Route

Sperm cells are carried through the lumen in the seminiferous tubules then…

Are stored and gain motility in the epididymis. Upon arousal, the sperm moves up the vas deferens

into the sperm duct The seminal vesicle pumps fluid (containing high

fructose levels to help sperm respirate) into the sperm duct.

The sperm duct travels into the prostate gland… The prostate adds alkaline (basic) fluid to help the

sperm resist the acidity of the vagina. Then it exits the male from the prostate and out the

urethra.

Side Note: The bulbourethral gland is located along

the urethra and below the prostate. Prior to ejaculation, the gland secretes a

clear mucus. The mucus neutralizes any acidic urine

left in the urethra. Fun Fact: The mucus does contain some

sperm which is why the pullout method of birth control has a high failure rate.

Female Anatomy

Head On View

Hormones in Menstrual Cycle

Animation: https://www.youtube.com/watch?v=l_wX285vrrU

Hormone Changes

Diagram of Ovary

Function of Ovary Parts 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

Oogenesis

The second meiotic division is not completed until fertilization.

Processes Involved in Oogenesis

Oogenesis describes the production of female gametes (ova) within the ovary

The process begins during foetal 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 fertilisation) It is released from the ovary (ruptured follicle develops into corpus luteum)

and, if fertilisation occurs, will complete meiosis The second meiotic division will produce an ovum and a second polar body

Mature Egg

Fertilization

In-Vitro Fertilization

In-Vitro Fertilization (IVF) For a period of three weeks, the women has to have a drug injected to stop

her normal menstrual cycle.  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.  HCG (another hormone) is injected 36 hours before the collection of the eggs.

HCG loosens the eggs in the follicles and makes them mature.  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.  A device that is inserted through the wall of the vagina is used to extract the

eggs from the follicles.  Each egg is then mixed with sperm in a shallow dish. The dishes are then put

into an incubator overnight.  The next day the dishes are looked at to see if fertilization has happened.  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. A pregnancy test is done a few weeks later to find out if any of the embryos

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

normally.

Ethical Issues of IVFArguments 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. 

Compare Spermatogenesis and Oogenesis

Similarities: Both processes result in the formation

of haploid gametes Both processes involve mitosis, growth

and meiosis

Differences

Process of Fertilization

Process of Fertilization 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) Fertilisation 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 fertilised 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 fertilised, the nucleus of the secondary oocyte completes meiosis II and

then the egg and sperm nuclei fuse to form a diploid zygote

Role of HCG in Pregnancy

Fun Fact: Human chorionic gonadotrophin, this is what is tested in pregnancy tests.

HCG 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

Early Embryo Development

Early Embryo Development After fertilisation, 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)

Role of the Placenta

Structure and Function of Placenta 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 of Placenta 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

Role of 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

Fetus.

Material Exchange Between Mother and Fetus

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

Birth and Hormonal Control

Child Birth! 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 labour is complete and the baby is birthed (no

more stretching of the uterine wall)

Final Thoughts!http://www.youtube.com/watch?v=Xath6kOf0NEhttp://www.youtube.com/watch?v=sPk_WM1ki4s