Fetal
Development
The Placenta




Mammalian structure that functions in gas,
nutrient, and waste exchange between the
embryo (later fetus)and mother’s
cardiovascular systems
First are chorionic villi (treelike projections)
that project into endometrium
Later, these disappear except where the
placenta is formed
By Week 10, the placenta is fully formed and
is producing estrogen and progesterone
The Placenta cont.
 Two
effects of these hormones:
1) negative feedback control of
hypothalamus and anterior pituitary 
prevention of any new follicles from
maturing
2) Maintain the uterine lining so that the
corpus lutuem is no longer needed
No menstruation during pregnancy!
More of the placenta





Fetal side = chorion
Maternal side = uterine tissues
Note: the chorionic villi are surrounded by
maternal blood BUT maternal and fetal blood
do not mix under normal conditions because
exchange happens over plasma membranes
C02 and other wastes go from the fetal to the
maternal side
Nutrients and oxygen go from the maternal
side to the fetal side
Umbilical Cord





The umbilical cord connects the placenta and the
fetus and takes fetal blood to and from the placenta
Lifeline of the fetus
Contains umbilical arteries and vein (transport these
wastes and nutrients in and out with placenta acting
as gatekeeper)
If the placenta tears from the uterine wall
prematurely, the lives of mother and child are at risk
Another concern is harmful chemicals crossing the
placenta, especially during the embryonic period
when many structures are forming, although each
organ has a sensitive period
Fetal Development
 Fetal
development occurs from month 3
to month 9. There is a drastic size increase
– weight multiplies 600 times (28 grams to
3 kilograms) and the fetus grows about 50
cm in length.
 The genitals grow in the third month so the
sex can be determined at that time.
 After that, hair, eyebrows, eyelashes,
toenails, and fingernails grow.
Fetal Development cont.





Lanugo (fine downy hair) covers arms and
torso.
Vernix caseosa (waxy substance) protects skin
from amniotic fluid
The skin is wrinkly because the fetus is growing
so quickly.
At month four, the fetus has increased
movement which is why the mother begins to
feel it at this time.
At the end of month four, the heartbeat can
be heard with a stethoscope.
The Birth
Process
The Stages of Birth



Latest findings: when the fetal brain is mature
enough, the hypothalamus causes the
pituitary gland to stimulate the adrenal cortex
which releases androgens into the
bloodsteam that the placenta uses to make
estrogens
These estrogens catalyze the production of
prostaglandin and oxytocin
These hormones cause contractions in the
uterus that will push the fetus out.
The Stages of Birth cont.
 Parturition
1.
2.
3.
(process of birth) – 3 stages
The cervix dilates to allow the baby’s
head and body to pass. This stage is also
typically when the amnion bursts.
The baby is born and the umbilical cord
is cut.
The placenta is delivered.
Infertility
 The
inability of a couple to achieve
pregnancy after one year of regular,
unprotected intercourse
 Some infertility can be solved by females
taking fertility drugs that have hormones
stimulating the ovaries to cause ovulation
 Others will decide to adopt
Artificial Insemination by
Donor (AID)
 Sperm
is placed in the vagina by a doctor
 Helpful if the male has a low sperm count
because the sperm can be collected
over time
 Sperm can be sorted through a DNAstaining chemical into those thought to
be X-bearing or Y-bearing to increase
chances of having a child of that sex if
the parent(s) desire
In Vitro Fertilization (IVF)




The sperm and the egg unite outside of the
body
Ultrasounds pick out follicles in the ovaries that
hold immature ooctyes that are brought to
maturity in glassware before the sperm is
added
After two to four days, the embryos are
placed in the uterus
This method is useful to overcome issues
involving conception, including blocked
oviducts
In Vitro Process
1.
2.
3.
4.
Week 1. A drug is injected daily for three
weeks that stops the woman’s normal
menstrual cycle.
Week 4. FSH is injected in large doses daily
for 10 to 12 days. This stimulates the ovaries
so they will develop lots of follicles.
Week 5. HCG is injected 36 hours before the
egg collection. This loosens the egg in the
follicles and matures it.
Week 5. The man provides semen and it is
processed to pool the healthy sperm.
In Vitro Process cont.
5. Week 5. The eggs are taken out of the follicles.
6. Week 5. Each egg is mixed with sperm. They are
placed in shallow dishes that sit in an incubator over
night.
7. Week 5/6. Check the dishes!!
8. Week 5/6. Two or three embryos are picked and
put into the uterus.
9. Beginning of week 8. A pregnancy test is done to
see if any implanted.
10. End of week 9. If so, a scan is done to ensure that
the pregnancy is normal. The fetal heartbeat should
be present.
Ethical Issues – IB Standards
 Aim
8: There is great variation between
human societies around the world on the
views held on IVF. This is the result of
cultural and religious diversity. There is little
evidence to suggest that children born as
a result of standard IVF protocols are
different in any way from children
conceived naturally. It is important that
there is parity of esteem for all children,
however they are conceived.
Ethical Issues – IB Standards
 TOK:
There are potential risks in the drug
treatments that the woman is given, and
there are concerns about the artificial
selection of sperm and the injection of
them into the eggs that occurs with some
IVF protocols. The natural selection of
sperm with consequent elimination of
unhealthy ones is bypassed and there is
evidence that there are higher rates of
abnormality in the offspring as a result.
Ethical Issues
Against IVF





Inherited forms of infertility may be
passed on to children.
Extra embryos are sometimes killed.
Embryologists pick which embryos
to transfer to the uterus so humans
decide which ones live and die.
IVF is an unnatural process
occurring in a lab, not an act of
love with natural conception.
Infertility should be accepted as the
will of God and it is wrong to use IVF
to circumvent it.
For IVF





Many forms of infertility are
because of the environment so
children won’t get them.
The embryos cannot feel pain or
suffer because they don’t have a
nervous system.
Suffering because of genetic
disease could decrease because
embryos are screened.
Parents willing to go through IVF
really want kids and will probably
be good parents.
Infertility makes many people
unhappy and IVF can overcome
this.
Animal
Reproduction
Asexual Reproduction






Sponges: asexual gemmules  new individuals
Cnidarians (ex. Hydra): budding
Flatworms: parasitic and reproduce during certain
stages of their life cycles
Annelids and echinoderms (ex. starfish): regenerate
from fragments
Parthenogenesis – modification of sexual
reproduction in which an unfertilized egg develops
into a complete individual
Example – the queen honey bee will make and store
sperm that she will selectively use to fertilize eggs;
any unfertilized egg will become a haploid male
Sexual Reproduction
 The
egg of one parent is fertilized by the
sperm of another
 Most animals are dioecious (separate
sexes); some are monoecious or
hermaphroditic (both female and male
sex organs in the same body)
 Some monoecious organisms self fertilize
(ex. Tapeworm) while others cross fertilize
(ex. Earthworms)
Sexual Reproduction





Animals typically produce gametes in gonads
(specialized organs – testes and ovaries)
Many aquatic animals practice external
fertilization
Copulation – sexual union to faciliate the
reception of sperm by a female
Terrestrial vertebrates – males usually have a penis
to deposit sperm into the vagina of females
Birds – lack a penis and vagina and instead have
a cloaca (chamber that receives products from
the digestive, urinary, and reproductive tracts)
that the two sexes press together
Life History Strategies




Oviparous – animal will deposit egg into
external environment (most aquatic animals)
Most oviparous animals have a larval stage
(immature form capable of feeding)
Extraembryonic membranes – contained in
leathery-shelled eggs to protect and help the
embryo; typically found in reptiles
Viviparous – placental mammals; do not lay
eggs and development occurs inside the
female’s body until offspring can live on their
own