Biology 3201
Unit 2 – Reproduction &
Development
Chapter 15
Continuance of Human Life
Ms. K. Morris 2010-2011
Section 15.1:
The Human Reproductive System
p. 486-499
The Human Male Reproductive System
Male Sexual Structures
• Sperm pass through the sperm duct (vas deferens)
and connect to a short ejaculatory duct that
connects to the urethra.
• The urethra passes through the penis and opens to
the outside. Secretions from the seminal vesicles
add fructose and prostaglandins to sperm as they
pass.
• The prostate gland secretes a milky alkaline fluid.
• The Cowpers (bulbourethral) gland secretes a
mucus-like fluid that provides lubrication for
intercourse. Sperm and secretions make up semen.
• Testes are suspended outside the abdominal
cavity by the scrotum, (for an optimal
temperature for sperm development).
• Seminiferous tubules are inside each testis,
and are where sperm are produced by
meiosis. Spermatocytes inside the tubules
divide by meiosis to produce spermatids that
in turn develop into mature sperm.
• Sperm production begins at puberty and
continues throughout life, with several
hundred million sperm being produced each
day.
• Once sperm form they move into the
epididymis, where they mature and are
stored.
• Four sperm are produced per meiosis. Sperm
are small, motile and contain an enzyme filled
acrosome that allows it to digest through the
egg.
• Testes- produces sperm and reproductive hormones.
They hang outside the body cavity within the scrotum
so that they have a cooler temperature for the
formation of healthy sperm. Testes develop inside the
body but descend during the last two months of fetal
development. Sterility usually results if the testes fail
to descend, but this can be corrected surgically.
• Scrotum- sac that contains the testes outside the
body.
• Seminiferous Tubules- long coiled tubules which
makes up the testes. It is here that spermatogenesis
occurs. The lining of each of these tubules is
composed of cells undergoing meiosis and sperm are
continuously produced and released from the inner
lining.
• Epididymis- as sperm are formed they move to the epididymis
where they mature and become motile.
• Sperm Duct (vas deferens)- the tube that leads upward from
the testes into the abdominal cavity where it joins the
urethra.
• Penis -male reproductive organ.
• Cowpers Gland and Prostate Gland -produce an alkaline fluid
which neutralizes acids in the female reproductive tract.
• Seminal Vesicles- provide a mucus like fluid containing
fructose which provides energy for the sperm.
• Cowpers gland, prostate, and seminal vesicles secrete fluid
into the urethra (also the tube where urine exits the bladder
and combine with sperm to produce semen).
Male Reproductive Hormones:
(1) Follicle Stimulating Hormone (FSH)- stimulates spermatogenesis
from the anterior pituitary.
(2) Inhibin- released by the seminiferous tubules and forms a negative
feedback loop with FSH. It acts on the hypothalamus to slow the
production of releasing factors that control the release of FSH.
Interaction of inhibin and FSH controls the rate of formation of
sperm.
(3) Luteinizing hormone (LH)- also from anterior pituitary, stimulates
the interstitial cells of the testes that surround the seminiferous
tubules to produce male sex hormones.
(4) Testosterone - the major androgen (male sex hormone) and is
responsible for the development of male secondary characteristics
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enlargement of penis and testes
enlargement of the larynx (Adams apple)
inhibits fat and promotes development of muscle tissue
stimulates formation of the face, chest, underarms and genitals
levels of testosterone in the blood inhibits the production of LH
Male Sex Hormones…
• The anterior pituitary produces folliclestimulating hormone (FSH) and luteinizing
hormone (LH). Action of LH is controlled by the
gonadotropin-releasing hormone (GnRH). LH
stimulates cells in the seminiferous tubules to
secrete testosterone, which has a role in sperm
production and developing male secondary sex
characteristics. FSH acts on cells to help in
sperm maturation. Negative feedback by
testosterone controls the actions of GnRH.
The Human Female Reproductive System
• The ovary contains many follicles composed
of a developing egg surrounded by an outer
layer of follicle cells. Each egg begins
oogenesis as a primary oocyte.
• At birth each female carries a lifetime supply
of developing oocytes, each of which is in
Prophase I.
• A developing egg (secondary oocyte) is
released each month from puberty until
menopause, a total of 400-500 eggs.
• Ovary- production of female gametes (ova).
• Follicles- tiny egg sac in ovary. They are composed of
many groups of cells, each of which contains a single
ovum.
• Oviduct (Fallopian tube)- tube which carries the egg into
the uterus or womb. The lining of each tube is ciliated to
created a current that moves the egg toward the uterus.
• Ova are released from different parts of the ovaries so the
openings of the oviducts consist of finger like projections
called fimbriae which sweep over the ovaries. They are
also ciliated to sweep an ovum into an oviduct for its trip
to the uterus.
• Uterus- fist sized organ with thick muscular walls; receives
a fertilized egg for further development (embryo implants
inside the uterus).
• Endometrium- lining of the uterus containing many blood
vessels that can nourish the developing embryo. It is
affected by the changing hormone levels during
menstruation.
• Cervix- forms the opening or exit to the uterus.
• Vagina- what the cervix extends downward into the birth
canal and leads to the outside of the female body.
• Note: human female has two separate openings for
urinary and reproductive function. Also the vagina has
two functions:
– (1) Allows entry of sperm into female body
– (2) Exit of baby during birth
Ovarian Cycles
• After puberty the ovary cycles between a follicular phase
(maturing follicles) and a luteal phase (presence of the corpus
luteum).
• These cyclic phases are interrupted only by pregnancy and
continue until menopause, when reproductive capability ends.
• The ovarian cycle lasts usually 28 days. During the first phase, the
oocyte matures within a follicle.
• At midpoint of the cycle, the oocyte is released from the ovary in
a process known as ovulation.
• Following ovulation the follicle forms a corpus luteum which
synthesizes and prepares hormones to prepare the uterus for
pregnancy.
• The uterus has an inner layer, the endometrium, in which a
fertilized egg implants.
• At the lower end of the uterus the cervix connects the uterus to
the vagina.
Hormones and Female Cycles
(FSH, LH – pituitary)
(progesterone, estrogen – ovarian)
• The ovarian cycle is hormonally regulated in two phases.
The follicle secretes estrogen before ovulation; the corpus
luteum secretes both estrogen and progesterone after
ovulation.
• The ovarian cycle covers events in the ovary; the
menstrual cycle occurs in the uterus. The menstrual
cycles’ first day of blood flow (day 0) known as
menstruation.
• During menstruation the uterine lining is broken down
and shed as menstrual flow. FSH and LH are secreted on
day 0, beginning both the menstrual cycle and the ovarian
cycle.
• Both FSH and LH stimulate the maturation of a single
follicle in one of the ovaries and the secretion of
estrogen.
• Rising levels of estrogen in the blood trigger secretion of
LH, which stimulates follicle maturation and ovulation
(day 14, or mid-cycle).
• LH stimulates the remaining follicle cells to form the
corpus luteum, which produces both estrogen and
progesterone.
• Estrogen and progesterone stimulate the development
of the endometrium and preparation of the uterine inner
lining for implantation of a zygote.
• If pregnancy does not occur, the drop in FSH and LH
cause the corpus luteum to disintegrate.
• The drop in hormones also causes the sloughing off of
the inner lining of the uterus by a series of muscle
contractions of the uterus.
Female Hormone Treatments
• With age there is a decrease in the number of
functioning follicles and therefore a decrease of
estrogen and progesterone in the blood. This signals
the onset of menopause, characterized by the
cessation (stopping) of menstruation.
Menopause Characteristics:
– cholesterol levels rise and bone mass declines
– blood vessels alternately constrict and dilate causing “hot
flashes”
– mood changes
Some doctors prescribe hormone replacement
therapy in the form of low levels of estrogen and
progesterone
Benefits of hormone replacement:
– relief of menopausal symptoms such as hot flashes, night
sweats and sleep disruptions
– prevention of bone loss (osteoporosis)
– improved memory
– decreased chance of urinary tract infection
– decreased chance of macular degeneration (a leading cause
of blindness)
– the risks of hormone replacement vary with the hormone
prescribed
Potential side effects of estrogen replacement:
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irregular vaginal bleeding
stomach upset
severe headaches
formation of blood clots
increased risk of breast and uterine cancer
Potential side effects of progesterone replacement:
– stomach upset
– irregular vaginal bleeding
– edema (water retention)
Potential side effects of combined estrogen and
progesterone replacement:
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formation of blood clots
increased risk of heart attack during first year of treatment
headaches
fluctuation of blood sugar level
edema
pre-menstrual like syndrome
• Contraception is another application of female
hormones. Birth control pills contain a combination of
progesterone and estrogen or progesterone alone. Many
of the risks associated with birth control pills are similar
to risks associated with hormone replacement therapy.
• One form of birth control contains synthetic forms of
estrogen and progesterone. This pill is taken everyday for
the first 21 days of each menstrual cycle, the
combination of estrogen and progesterone suppresses
secretions of FSH and LH as a result:
– (1) Ovulation is inhibited
– (2) The hormones cause the endometrium to develop
abnormally so that if ovulation does occur the egg is fertilized,
implantation cannot occur.
Sexually Transmitted Infections (STI’s) p.496-499
(diseases spread through sexual contact )
• Most common STI’s are caused by viruses or bacteria. In
the past bacterial infections such as gonorrhea and
syphilis were deadly. Today they can usually be cured
using antibiotics. Viral infections such as AIDS and genital
herpes cannot be cured but can be treated.
1. AIDS and HIV
• AIDS: acquired immunodeficiency syndrome. Caused by
the virus HIV and attacks helper T cells of the immune
system. Low helper T cells in blood leaves person
susceptible to a variety of diseases and usually leads to
sickness and death.
Transmission of HIV:
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vaginal or rectal intercourse
oral/genital contact
sharing needles among intravenous drug users
blood transfusions (today blood is screened)
children of mothers who are infected with HIV may be infected
before or during birth
Three Stages of AIDS:
• Stage A- lasts about one year. No symptoms but may
infect others, and as long as the body produces enough
helper T cells the person remains well.
• Stage B- 6-8 years. Begins when body cannot replace T
cells fast enough
• Stage C: Nervous disorders such as pneumonia and skin
cancers. With no treatments the person will die in 6-7
years.
2. Hepatitis A, B and C
• A- contracted by drinking contaminated water (sewage) or
oral and anal contact
• B- spread the same way as HIV
• C- transmitted by infected needles or syringes
Symptoms:
• fever, headache, loss of appetite, abdominal pain and
yellowish skin (jaundice)
• may progress to cause infection of the liver, leading to liver
failure, liver cancer or death
• some people recover completely while others become
asymptomatic and infect others
• vaccines are available for A and B
• hepatitis viruses may cross the placenta to infect the unborn
child
3. Genital Herpes
• Caused by herpes simplex 1 (HSV1) or herpes simplex 2 (HSV2)
• HSV 1- commonly causes cold sores and fever blisters on the mouth
• HSV 2- likely acquired through sexual contact and may cause genital herpes
Symptoms:
• tingling or itching, followed by blisters which rupture
• blisters may appear on genitals, buttocks or thighs or internal tissues and sores
may take from three to five weeks to heal
• flu like symptoms
• blisters may reoccur with varying frequency or none at all
• lymph nodes swell and a person experiences weight loss, night sweats, fatigue,
fever and diarrhea
• infections such as thrush (fungal infection) and herpes
• no cure for genital herpes and once infected you are infected for life
• herpes sores mean a risk of aids infection
• if a newborn baby encounters a sore during birth the infection can cause
blindness, neurological disorders or even death
• mothers with genital herpes are encouraged to have caesarean sections
4. Chlamydia
• caused by bacteria
• men experience burning during urination and discharge from
the penis
• women may have vaginal discharge and symptoms or
urinary tract infection including pain on urination and fever
• one of the main dangers of Chlamydia is that 75% of cases
are asymptomatic which means that many suffers do not
have any symptoms until irreversible damage is done
• if undetected women may develop sores on the cervix and
oviducts, the patient may develop pelvic inflammatory
disease (PID) which is painful and may lead to blocked
oviducts.
• if infection is caught early enough it can be treated and
cured with antibiotics
• if a baby comes in contact with Chlamydia during birth it can
develop inflammation of the eyes or pneumonia
5. Syphilis
- caused by bacteria
Stage one: chancre sores appear at infection site
Stage two : rash appears (usually on palms or soles of feet but may
appear anywhere on skin) this stage is extremely infectious
Stage three: infection affects cardiovascular and nervous system and
may develop blindness, mental illness, and heart disease
• large destructive ulcers may develop on skin or internal organs
• can be treated with antibiotics it can be diagnosed with a blood
test, symptom recognition or microscopic identification of bacteria
• it must be treated early before the bacteria causes permanent
damage
• syphilitic bacteria may cause birth defects or stillborn
6. Gonorrhea
• caused by bacteria
• causes infection of the urethra, rectum, cervix and throat
• pain on urination and thick greenish yellow discharge
from the urethra
• some people have no initial symptoms
• women may develop PID and become infertile
• infection may spread to heart valves, joints, or brain
• many strains are resistant to traditional antibiotics
• babies passing through the birth canal of infected
mothers may develop eye infections leading to
blindness. Therefore, eye drops are given to newborns as
a means of prevention
Section 15.2:
Reproductive Control
p. 500-505
Identify the causes of human infertility. (p. 501-502)
In Females:
(i) Blocked Oviducts – often caused by PID (pelvic
inflammatory disease) which is often caused by
STI’s.
(ii) Failure to Ovulate – caused by hormonal
imbalances that occur for a variety of reasons,
including being underweight or overweight.
(iii) Endometriosis – a painful condition in which the
endometrium grows outside the uterus.
(iv) Damaged Egg – which may be caused by
environmental factors, such as exposure to
chemicals.
In Males:
(v) Obstruction in the Vas Deferens or Epididymis –
which may be caused by complications arising
from STI’s or from varicose veins in the testicles.
(vi) Low Sperm Count – caused by numerous
factors, including overhead testicles, smoking,
and alcohol intake.
(vii) Abnormal Sperm – caused by factors including
overheated testicles, exposure to toxins, and
infections, such as STI’s.
Technological solutions to human infertility:
(p. 501, Table 15.1)
(i) Artificial Insemination (AI) – Sperm is placed
into the vagina by a physician. Used by: an
infertile couple, men with low sperm count,
women without male partners.
(ii) In Vitro Fertilization (IVF) – Fertilization takes
place outside the body, in a laboratory
procedure. The fertilized oocytes are
implanted in the uterus. Used by: a woman
who has damaged or blocked oviducts.
(iii) In Vitro Maturation (IVM) – Primary follicles
are removed from the uterus and induced to
mature into secondary oocytes. IVM is used to
produce numerous oocytes for in vitro
fertilization. Used by: a woman who will
undergo in vitro fertilization.
(iv) Surrogate Motherhood – A fertilized oocyte from
an infertile couple (obtained by IVF) is placed in the
uterus of a surrogate mother. Alternatively, a
surrogate mother undergoes AI, using sperm from
the male of the infertile couple. Used by: a woman
who cannot bring a child to term, or a couple who is
infertile due to unknown factors or factors that
cannot be overcome by other technologies.
(v) Superovulation (using fertility drugs) – Used to
produce multiple eggs for in vitro fertilization, to
increase the chance of pregnancy. FSH (follicle
stimulating hormone) injections stimulate the
development of multiple follicles. Cont’….
…HCG (human chorionic gonadotrophin)
stimulates ovulation. Used by: a woman who is
undergoing in vitro fertilization, or a woman who
does not ovulate regularly, frequently, or at all, to
increase her chances of pregnancy.
(vi) Embryo Storage (Cryopreservation) – Oocytes,
semen, and even embryos are preserved by
freezing. Used by: a male or female cancer patient,
who may become infertile or sterile due to
radiation therapy, or a sperm bank that supplies
semen for AI.
Evaluate the design of birth control technologies
and the way they function. Include: (p. 502)
A) Barrier Methods:
1. Male Condom – about 85% effective. A latex
sheath that fits over the erect penis. It traps the
sperm. Risk is a reaction to latex.
2. Female Condom – about 85% effective. A
polyurethane pouch that is inserted into the
vagina. It prevents the sperm from contacting
the vagina and cervix. No known risks.
3. Diaphragm – about 90% effective. A large latex
cup that fits over the cervix and prevents sperm
from entering. It is usually used with
spermicidal jelly or foam. Sperm is blocked at
the cervix. Risks are reaction to latex.
4. Cervical Cap – almost 85% effective. Must be
used with the jelly. A latex cap is attached to
the cervix by suction. Sperm is blocked, and
killed by the spermicide, at the cervix. Risks are
reaction to latex.
5. Spermicidal Jellies & Foams – about 75%
effective. These products are inserted into the
vagina before intercourse. They are often used
with a condom or diaphragm. A large percent
of sperm are killed. Risk is reaction to
spermicide.
6. IUD (interutine device) – over 90% effective.
An IUD is a plastic coil or armature that is
inserted into the uterus. It lasts about 5 years.
Implantation (of the egg) is prevented. Risk is
PID (pelvic inflammatory disease).
B) Hormonal Methods:
7. Birth Control Pill – close to 100% effective (if used
correctly). A daily hormone medication taken orally. FSH
and LH are not released. Risks include blood clots
(especially in smokers), and hormonal side effects.
8. Morning After Pill – close to 100% effective (if taken
properly). It can be taken up to 3 days after possible
fertilization but the sooner it is taken the higher the
success rate. Contains high doses of estrogen and
progesterone. Prevents or delays the release of oocyte
from ovary and if fertilization occurred it stops embryo
from implanting in the endometrium. Side effects:
nausea and vomiting.
9. Norplant (implant) – over 90% effective.
Hormones are implanted under the skin. FSH
and LH are not released. Risks are hormonal
side effects.
10. Depo-Provera (needle) - 99% effective. A
woman is given one hormone injection every
three months. FSH and LH are not released.
Risks are hormonal side effects.
C) Surgical Methods:
11. Tubal Ligation – close to 100% effective. The
oviducts are cut and tied. The eggs do not reach
the oviduct or uterus. Risks are that it is
permanent, irreversible, and sterility.
12. Vasectomy – close to 100% effective. The
sperm ducts are cut and tied. There is no sperm
in the ejaculate. Risks are that it is permanent,
irreversible, and sterility.
D) Other:
13. Rhythm Method – about 70% effective. The
date of ovulation is determined by record
keeping and temperature measurements.
Intercourse is avoided at the most fertile
times. No risks.
14. Abstinence - 100% effective. The woman
must refrain from sexual intercourse. Sperm
does not contact the vagina. No risks.
• Assess the effects of birth control technology on the
population demographics of developed and
underdeveloped countries & debate the merits of funding
solutions to human fertility problems versus human
population control. (Read p. 503-505)
– Investigate the methods of population/birth control of
various countries around the globe and assess the
effects of these conception control population
technologies on the demographics of these countries.
• China: 1 child per family rule
• Selection of 1 gender (usually male) and abortion of females
in some developing countries
Recall: Demographic Transition…
• Stage 2 is a period of rapid population growth
and in stage 3 birth rates begin to decline.
• Moving from stage 2 to stage 3 depends
largely on contraceptive technologies.
• More industrialized countries are in stage 3 of
demographic transition, whereas many less
industrialized countries (like some in Africa and
Asia) remain in stage 2 (rapid population
growth).
• The reason for this is the availability of
improved contraceptive technologies.
• Drop is birth rate is possible with improved
contraception, but yet some countries remain in
stage 2. Why?
– It is not enough for effective contraception to exist.
– People must know that it exists and they must know
how to use it.
– It must be accessible to the people who want to use it
(and this is not the case in less industrialized nations,
especially poor people).
– People must also want to have fewer children (cultural
attitudes must change).
– A power and education imbalance between women
and men can affect contraception use as well.
Section 15.3:
Development & Differentiation
p. 506-514
• Explain the processes of fertilization and
development in human reproduction. Trace the
journey of sperm and egg from their origin until
fertilization and implantation.
- Describe the following basic stages of embryonic
development. (p. 508)
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(i) cleavage
(ii) morula
(iii) blastocyst (blastula)
(iv) gastrula
(v) germ layers
(vi) neural development p. 509
• Development (fertilization, cleavage, blastulation,
gastrulation, neurulation, organogenesis)
• Fertilization - Contact between sperm and egg; entry of
sperm into the egg and fusion of egg and sperm nuclei
(upper third of the oviduct).
• One sperm fuses with receptors on the surface of the
secondary oocyte, triggering a series of chemical changes in
the outer oocyte membrane that prevent any other sperm
from entering the oocyte.
• The entry of the sperm initiates Meiosis II in the oocyte.
• Fusion of the egg and sperm nuclei forms the diploid
zygote.
• Cleavage converts a single-celled zygote into a multicelled embryo by mitosis.
• The blastula is produced by mitosis of the zygote, and is
a ball of cells surrounding a fluid-filled cavity (the
blastocoel).
• Gastrulation involves a series of cell migrations to
positions where they will form the three primary cell
layers:
– Ectoderm forms the outer layer - skin, epithelium, brain and
nervous system
– Endoderm forms the inner layer - digestive and respiratory
systems
– Mesoderm forms the middle layer - body muscles, cartilage,
bone, blood
• Organ formation occurs in the next stage of the
development of the embryo.
• Induction is the process in which one cell or tissue type
affects the developmental fate of another cell or tissue.
Induction affects patterns of gene expression through
physical contact or chemical signals. Formation of the
vertebrate eye is a well known example.
Travels of a Young Zygote
• Cleavage of the zygote begins while it is still in the
oviduct, producing a solid ball of cells (morula). The
morula enters the uterus, continuing to divide and
becomes a blastocyst.
Identify chemical control hormones
associated with implantation, birth and
lactation. Include:
– (i) progesterone
– (ii) estrogen
– (iii) oxytocin
– (iv) prolactin
– (v) human chorionic gonadotropin (HCG)
– This outcome is addressed in the notes that
follow…
Implantation
• The uterine lining becomes enlarged and
prepared for implantation of the embryo in the
trophoblast layer.
• Twelve days after fertilization, the trophoblast has
formed a two-layered chorion.
• Human chorionic gonadotropin (hCG) is secreted
by the chorion, and prolongs the life of the corpus
luteum until the placenta begins to secrete
estrogen and progesterone.
• Home pregnancy tests work by detecting elevated
hCG levels in the woman's urine.
p. 509-510:
The First Trimester (Weeks 1-12)
• The three embryonic tissue layers form (ectoderm, mesoderm and
endoderm). Cellular differentiation begins to form organs during
the third week. During the second month most of the major organ
systems form, limb buds develop. The embryo becomes a fetus by
the seventh week.
The Second Trimester (Weeks 13-24)
• The fetus increases in size during this trimester, and bony parts of
the skeleton begin to form. Fetal movements can be felt by the
mother.
The Third Trimester (Weeks 25-38)
• During this trimester the fetus increases in size. Circulatory and
respiratory systems mature in preparation for air breathing. Fetal
growth during this time uses large parts of its mother's protein
and calcium intake.
Describe the process of childbirth. Include:
• (i) dilation stage
• (ii) expulsion stage
• (iii) placental stage
Birth (p. 512-513)
• Birth is a positive feedback hormonal mechanism.
During birth, the cervix dilates to allow passage of the
fetus. Uterine contractions propel the fetus through
the birth canal, usually head first. Hormonal control of
the birth process involves the release of oxytocin and
prostaglandins.
1) Dilation - dilation of the cervix. Membranes of the
amniotic fluid rupture, lubricating the vagina.
2) Expulsion - Strong uterine contractions of a minute
in duration separated by two to three minute
intervals propel the fetus down the birth canal.
3) Placental –The placenta (or afterbirth) in expelled
through the vagina.
• Secretion of milk does not occur until delivery, and
the action of prolactin. Suckling by the infant causes
production of oxytocin to promote release of milk
into the ducts emptying into the nipple.
Explain how fraternal and identical offspring are
produced: p. 507
Fraternal Twin
• more than one egg is released from the ovary at the same
time
• two eggs become fertilized at the same time
• two children will be born at the same time but they will be
different since they developed from two different egg and
sperm
Identical Twin
• zygote splits into two separate bodies during early
development
• these children will be the same and are genetically equal
since they developed from the same zygote
Describe the functions of primary membranes during the
embryonic development of animals:
Development of the fetus can be compared to a chick embryo:
1. Chorion is the layer located just inside the shell. It surrounds
the embryo and other membranes. It controls the exchange of
gases.
2. Allantois is a sac-like structure that grows out of the digestive
tract of the embryo. It exchanges gases and collects the waste
material of the embryo.
3. Amnion is a sac that surrounds the embryo. It is filled with
fluid and keeps the embryo moist. It also cushions the embryo
for protection.
4. Yolk sac holds the yolk. The yolk is food for the embryo. The
embryo consumes all of the yolk before hatching.
Describe the roles of the placenta and umbilical cord
during pregnancy:
• During three trimesters, the fetus needs to be nourished,
get oxygen and get rid of waste. These functions are
performed by the placenta and the umbilical cord.
• Maternal and embryonic structures interlock to form the
placenta, the nourishing boundary between the mother's
and embryo's systems.
• The umbilical cord extends from the placenta to the
embryo, and transports food to and wastes from the
embryo.
• Placenta - a blood vessel-rich organ which is present only during
pregnancy.
• Begins to form from the chorion once fully implanted.
• Chorion develops projections which extend into the uterine wall
serving as an anchor. These projections contain blood vessels
which, with the chorion, form the placenta.
• Placenta is fully formed after the tenth week.
• During and after development it produces estrogen and
progesterone (prevents any new follicles from maturing and
maintain uterine lining).
• No ovulation or menstruation due to high levels of progesterone
and estrogen in the blood.
• The placenta is what the embryo of the fetus depends on for
survival. It is where it gets all the nutrients and oxygen and all
wastes are removed.
• Umbilical Cord - it is a lifeline, connecting the
developing embryo and fetus to the placenta.
• The mother’s blood and the fetus’s blood never
mix, but the transfer of nutrients and oxygen
from the mother to the fetus, and the transfer of
carbon dioxide and other waste substances from
the fetus to the mother take place across plasma
membranes.
Examine the effects of teratogens on the
development of the embryo:
• Teratogen- any agent that causes a structural
abnormality due to fetal exposure during pregnancy.
1. Cigarette Smoke - may constrict fetus’s blood
vessels preventing the fetus from getting enough
oxygen.
• Mothers who smoke or who are exposed to a lot of
second hand smoke may have babies that are under
weight.
• Also, the babies may suffer convulsions.
2. Alcohol - can affect the fetus’s brain, CNS, and
physical development.
• Babies that are born to women who drink
frequently or heavily during pregnancy are likely
to have fetal alcohol syndrome (FAS).
FAS babies:
• decreased height, weight and head size
• head and face may be deformed
• may show varying degrees of mental retardation
• may show unusual aggression or have personality
disorders
3. Prescription Drugs
• For example, thalidomide. Prescribed to pregnant
women in the 1950's to prevent morning sickness.
• At that time it was thought to have no side effects.
Doctors did not know it was teratogenic.
• Thalidomide caused the babies to be born with
deformed or missing limbs.
• Pregnant women should always check to see if
medication is safe for her developing baby.
• Other teratogenic factors:
– radiation (x-rays)
– pollutants
4 techniques used to monitor various stages of
embryonic or fetal development:
1. Ultrasound
• Sound waves beyond the level of human hearing are
sent through amniotic fluid.
• Waves bounce off the developing fetus and are used
to create a black and white, cross-sectional image of
the fetus.
• Image can be studied for physical abnormalities such
as a missing limb, malformed heart, or cleft palate.
2. Amniocentesis
• As a fetus moves inside amniotic sac some of its cells are
sloughed off and become suspended in amniotic fluid.
• A sample of this will give enough cells so that a karyotype
which can be used to check chromosomes for number.
• Cannot be done before the 14th week of pregnancy due
to possible injury to the fetus.
• A sample is taken with a long thin needle after the
position of the baby is determined by ultrasound.
• The sample of fluid is extracted, placed in a nutrient rich
solution and allowed to multiply until there are enough
fetal cells to get a good picture of all the chromosomes
and create a karyotype.
3. Fetoscopy
• Direct observation of the fetus occurs because of the
insertion of an endoscope (long tube with a camera
on one end) into a small incision in mother’s
abdomen.
• Enables procedures to take place inside womb such
as removal of excess brain fluid and fetal blood
transfusions.
• Also provides a way to get blood samples to create a
karyotype or to test genetic conditions such as Rh
factor or sickle cell disease.
4. Chorionic Villi Sampling (CVS)
• Amniocentesis cannot be done until 14th week and
there is potential danger involved and it may take weeks
to obtain results. Therefore:
• Chorionic villi sampling may occur after the 9th week
and cells can be removed from the chorion.
• The chorion surrounds amniotic sac and is one of the
tissues which makes up the placenta, which connects
mother’s blood with fetal blood.
• The chorion is made of fetal cells and also contains
genetic information about the fetus.
• Removed cells are grown in a special medium and a
karyotype allows a diagnosis to be made.