Human Reproduction and
Development
 Fertilization
 Pregnancy
 Development
 Birth
Human Reproduction and
Development
Sperm
Human Reproduction and
Development
3 Steps of Fertilization
1. Capacitating
– Acidic environment of the female
reproductive tract causes small
pores to open in the acrosome
(“enzyme-loaded” head) of the
sperm
3 Steps of Fertilization
3 Steps of Fertilization
1. Capacitating
– Acidic environment of the female
reproductive tract causes small
pores to open in the acrosome
(“enzyme-loaded” head) of the
sperm
2.
Acrosomal reaction
– Enzymes released from acrosome digest
the outer membrane surrounding the egg
cell
3 Steps of Fertilization
3. Fertilization
– A single sperm cell fuses with the
plasma membrane of ovum
– Head passes into the cytoplasm
– Electrochemical reaction in egg
• Makes membrane
impermeable to other sperm
Fertilization
•
Fertilization must occur within a
very short window of opportunity.
– Egg is only fertile for 12-24 hours
– Sperm can survive up to 5 days in
the body
– Sex (copulation) must occur no
more than 5 days before or 1 day
after ovulation
Pregnancy
• If pregnancy is established, menstruation does not
occur.
• Fertilized egg is called a zygote.
– Once cell division brings the total cell count to
around 8, it is called a blastocyst.
• Takes 3-5 days for blastocyst to travel through
oviduct to uterus.
• Blastocyst must implant into endometrium
– Occurs 2-4 days after reaching the uterus
Fertilization
• If pregnancy is established, menstruation does not
occur.
• Fertilized egg is called a zygote.
– Once cell division brings the total cell count to
around 8, it is called a blastocyst.
• Takes 3-5 days for blastocyst to travel through
oviduct to uterus.
• Blastocyst must implant into endometrium
– Occurs 2-4 days after reaching the uterus
Fertilization
• If pregnancy is established, menstruation does not
occur.
• Fertilized egg is called a zygote.
– Once cell division brings the total cell count to
around 8, it is called a blastocyst.
• Takes 3-5 days for blastocyst to travel through
oviduct to uterus.
• Blastocyst must implant into endometrium
– Occurs 2-4 days after reaching the uterus
Fertilization
• If pregnancy is established, menstruation does not
occur.
• Fertilized egg is called a zygote.
– Once cell division brings the total cell count to
around 8, it is called a blastocyst.
• Takes 3-5 days for blastocyst to travel through
oviduct to uterus.
• Blastocyst must implant into endometrium
– Occurs 2-4 days after reaching the uterus
Pregnancy
• During implantation, the blastocyst produces a
hormone called HCG
– Human chorionic gonadotropin
– Prevents degeneration of corpus luteum
– Stimulates corpus luteum to increase
progesterone secretion
• Maintains uterine lining
• Prevents contractions
– Pregnancy test detects HCG in the urine of
women.
• “Turns the stick blue”
Pregnancy
• Tissue grows out from the embryo and mingles
with endometrium to form placenta
– A disc-shaped organ
– Size of dinner plate
– Weighs less than 1 kg.
– Contains maternal & fetal blood vessels
• NO mixing of maternal and fetal blood!!
– Diffusion of gasses, nutrients, & wastes
– Continues production of HCG, estrogen,
progesterone
• Maintains endometrium
• Corpus luteum not needed – dissolves
Pregnancy
• Progesterone & estrogen have a
negative feedback effect on the
hypothalamus
– No secretion of FSH
– No secretion of LH
– No new follicles mature
• Embryo remains firmly attached to
placenta by umbilical cord.
Pregnancy
• Umbilical cord
–Contains:
• 2 fetal arteries
–Fetus to placenta
• One fetal vein
–Placenta to fetus
Pregnancy
Childbirth
•
•
Also called parturition
38 – 42 weeks from conception
– Average = 40 weeks
• Three stages of childbirth
1. Labour
2. Delivery
3. Afterbirth
Childbirth
1. Labour
– Involuntary
– Rhythmic contractions of the uterus
– Causes cervix to open
• Diameter = 10 cm
2. Delivery
– Involuntary uterine contractions
– Conscious abdominal contractions
– Mother forces baby out through cervix and
vagina
Childbirth
3. Afterbirth
– Immediately after delivery
– Blood vessels in placenta contract
– Placenta separates from uterine
wall
– Expelled by muscle contractions
Childbirth
• Why??
– Nobody totally knows.
– Baby plays some role in the timing.
– Progesterone decreases
• Allows uterus to contract
– Oxytocin from posterior pituitary
• Stimulates stronger uterine contractions
– Relaxin
• produced by placenta
• Causes ligaments of pelvis to loosen
• Larger passageway for baby
Lactation
• During pregnancy, high levels of estrogen and
progesterone prepare the breasts for milk
production
– Each breast has about 20 milk glands
– Connect to the nipple by ducts
– Breast enlarges during pregnancy in
preparation for lactation
• Expulsion of the placenta causes the mother's
pituitary to secrete prolactin,
– Initiates lactation
Lactation
• Prolactin inhibits the release of LH
– menstrual cycle is suppressed in
nursing mothers
• The high estrogen and progesterone
levels during pregnancy are thought
to inhibit release of prolactin
Lactation
• The first fluid formed by the mammary glands is
colostrum,
– Thick
– contains lactose and milk proteins,
– lacks fat
– after a few days, milk is produced
• Oxytocin is released from hypothalamus when
infant suckles
– Causes milk to be released from mammary
glands
Fetal Development
• A blastocyst
– embeds in the uterine wall
– Consists of cells of the future
embryo
– Surrounded by a sphere of cells
• Embryonic membrane (extraembryonic membrane)
• Support the developing embryo
Fetal Development
• Amnion
– Innermost embryonic membrane
• Next to baby
• Fluid-filled sac that cushions the
baby
Fetal Development
• Umbilical cord
– Connection between mother
and baby
• Belly-button to placenta
– Carries baby’s blood to and
from placenta
Embryonic Development
• Placenta (review)
– A disc-shaped organ
– Size of dinner plate
– Contains maternal & fetal blood vessels
• NO mixing of maternal and fetal
blood!!
– Diffusion of gasses, nutrients, & wastes
– Continues production of HCG, estrogen,
progesterone
Embryonic Development
•
A blastocyst undergoes gastrulation
–
Series of cell movements and shape changes
–
Produces an embryo with 3 cellular layers
1. Ectoderm
•
Outer layer of cells
•
Will become skin and nervous system
2. Mesoderm
•
Middle layer of cells
•
Skeleton, muscles gonads, kidneys, circulatory
system
3. Endoderm
•
Inner layer of cells
•
Liver, pancreas, lungs, lining of digestive tract
Gastrulation
Human Gestation
• 1st Trimester
–From fertilization to end of 3rd
month (0 – 13 weeks)
–Zygote begins cell division as it
moves down oviduct
–Becomes blastocyst and
implants in uterus
Human Gestation
• 1st Trimester
– Development of body organs
– Heart starts beating by week 4
– Week 7, testosterone begins to be
secreted if a Y-chromosome is
present
• This testosterone causes
development of testes.
Human Gestation
• 1st Trimester
– By week-8 all major structures of
the adult are present (in basic
form)
• Embryo is now called a fetus
– Embryo is most sensitive during
first trimester
• Due to rapid development
• Sensitive to radiation and drugs
Gastrulation
Gastrulation
6
weeks
7 weeks
Gastrulation
Gastrulation
8 Weeks
8 weeks
10 Weeks
11 Weeks
11 Weeks
14
Weeks
Human Gestation
• 2nd Trimester
– Fetus grows rapidly
• To about 30 cm
– Quite active
– Hair begins to develop
– Cartilage of skeleton is
replaced by bone
18 weeks
Gastrulation
The Hand Picture
May 2, 2000
USA Today
47
An Amazing Story -- Aug.19, 1999
• Samuel Armas' tiny hand grips Dr. Joseph P.
Bruner's finger just as Bruner finishes
returning him to his mother's womb.
• Bruner, director of fetal diagnosis and
treatment at Vanderbilt University Medical
Center (Nashville), was performing a
cutting-edge procedure on the 21-week-old
fetus.
• The procedure on Samuel took about an
hour.
48
An Amazing Story -- Aug.19, 1999
• Bruner and Samuel's parents hope the
surgery will alleviate the effects of spina
bifida, a disabling birth defect in one or two
of every 1,000 babies born.
• Because fetuses undergoing this procedure
are so young -- Samuel could not survive
outside his mother's womb -- this kind of
surgery is gaining attention nationwide from
the medical community and the media.
49
An Amazing Story -- Aug.19, 1999
• During the procedure, surgeons remove the
uterus from the mother, drain the amniotic
fluid, perform surgery on the tiny fetus,
replace everything and put the entire
package back inside the mother.
• Dr. Bruner said regarding the picture, "The
baby did not reach out," Bruner says. "The
baby was anesthetized. The baby was not
aware of what was going on."
50
An Amazing Story -- Aug.19, 1999
• Bruner says he saw the hand "sort of pop
up in the incision" on the womb, and he
"reached over and picked it up."
• Samuel, now nearly 5 months old [may 2,
2000], & is “developing normally and hitting
his monthly milestones. He smiles often and
is nearly sitting up on his own.”
• It will take years to know how much
difference the surgery made, but Alex
Armas [father] says he's happy the photo
has been seen by millions.
51
Samuel
Armas
21 weeks
Human Gestation
• 3rd Trimester
– Rapid growth of fetus
• To about 53 cm
• 3-3.5 kg
– Fetal activity decreases
• Less room to move
– Fully mature
– Ready for birth
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Parturition
Reproductive Technologies
Birth Control
• Sterilization
– Most effective
– In males vas deferens is cut off and
sealed
• Only effects sperm content of
semen so minimal side effects
– In females tubal ligation or cutting of
the oviducts
• Disadvantages of sterilization - hard to
reverse
Birth Control
• “The pill"
– A combination of estrogen and
progesterone given for 21 days of the
28 day cycle
– Effectively shuts down FSH and LH
production so follicles do not develop.
– Many of the early problems have been
sorted out but side effects possible
Birth Control
• Barrier Methods
– Diaphragms, Cervical Caps, Vaginal Sponges,
Condoms
• Condom
– fits over the penis and prevents semen from
entering the female;
• Diaphragm
– which fits over the cervix and prevents
semen from entering the uterus
• both of these methods are more reliable when
used in conjunction with a spermicidal foam or
jelly
Birth Control
• IUD
– Inter-Utarian Device
– placed in the uterus by a physician,
– prevent implantation of the blastocyst
in the endometrium.
– Best for women who have had one
pregnancy, middle to older and are at
low risk for STI’s
Birth Control
• "Natural family planning"
– Requires knowledge of the day of ovulation
– If known, can avoid the 4 days either side of
ovulation to account for unusually long -lived
sperm or eggs.
– Women need exceptionally regular cycles to
be effective
– "Basal" body temperature measurements (T
rises at ovulation), vaginal pH measurements
(more alkaline), mucus thickness can help
determine time ovulation.
Birth Control
• "Morning after pill“
– Most are essentially a controlled overdose of
normal birth control pills
– RU-486 now distributed by Planned
Parenthood.
– Blocks progesterone receptors causing
uterine lining to slough off taking embryo
with it.
– Many people have ethical problems with
these pills since they remove fertilized eggs.
• i.e. after "conception" has occurred.
• “abortion pill”
Reproductive Technologies
• Ultrasound
– the use of high-frequency sound waves to
visualize the fetus
• Amniocentesis
– a long needle is used to remove a sample of
amniotic fluid from the amniotic sac
surrounding the fetus,
– fetal cells in the fluid are cultured for 2 to 4
weeks and then analyzed for chromosomal
defects and other genetic disorders
Amniocentesis
Reproductive Technologies
• Chorionic Villi Sampling (CVS)
– a small sample of tissue is removed from the chorion,
• the fetal part of the placenta.
– Can be performed earlier in the pregnancy than
amniocentesis
– results can be obtained within a few days
– greater risk of spontaneous abortion from CVS than
from amniocentesis
– ethical considerations: essentially all detectable fetal
disorders remain untreatable in the uterus, and many
cannot be corrected even after birth
Reproductive Technologies
• In Vitro Fertilization
– ova can be surgically removed from a woman
whose oviducts are blocked
– These are fertilized in a petri dish in a
laboratory
– The resulting embryos can than be inserted
into the woman's uterus (or into a surrogate
mother's uterus)
– Ethical considerations: post-menopausal
woman can now have children; in surrogacy,
who is the legal mother???
STIs
Crabs
Epididimitis
Genital Warts
Syphilis
Gonorrhea
STIs
• Syphilis
– caused by a spirochete bacterium.
– The first symptoms of syphilis may go
undetected because they are very mild
and disappear spontaneously.
– The initial symptom is a chancre;
• usually a painless open sore that
usually appears on the penis or near
the mouth, anus, or on the hands.
STIs
– may go on to more advanced
stages, including a transient rash
and, eventually, serious
involvement of the heart and
central nervous system.
– The full course of the disease can
take years.
– Penicillin remains the most
effective drug to treat people with
syphilis.
Initial Chancre on Hand
STIs
• Gonorrhea
– discharge from the vagina or penis
• “Ooooze”
– and painful or difficult urination.
– The most common and serious complications
occur in women and, these complications
include PID, ectopic pregnancy, and infertility.
– Historically, penicillin has been used to treat
gonorrhea, but in the last decade, four types of
antibiotic resistance have emerged.
– New antibiotics or combinations of drugs must
be used to treat these penicillin resistant strains.
STIs
• Chlamydia
– many cases involve no symptoms and therefore
infected persons may not seek medical
treatment.
– This infection is now the most common of all
bacterial STD's, with an estimated 4 to 8 million
new cases occurring each year.
– In both men and women
– abnormal genital discharge
– burning with urination
– In women, untreated chlamydial infection may
lead to pelvic inflammatory disease,
• one of the most common causes of ectopic
pregnancy and infertility in women.
STIs
– Many people with chlamydial
infection, however, have few or no
symptoms of infection.
– Once diagnosed with chlamydial
infection, a person can be treated
with antibiotics
STIs
• Genital herpes
– Affects an estimated 60 million Americans.
– Approximately 500,000 new cases of this
incurable viral infection develop annually.
– Caused by herpes simplex virus (HSV).
– painful blisters or open sores in the genital area.
– These may be preceded by a tingling or burning
sensation in the legs, buttocks, or genital region.
– The herpes sores usually disappear within two to
three weeks, but the virus remains in the body
for life and the lesions may recur from time to
time.
STIs
• Genital herpes
– Severe or frequently recurrent genital herpes is
treated with one of several antiviral drugs that
are available by prescription.
• These drugs help control the symptoms but
do not eliminate the herpes virus from the
body.
• Suppressive antiviral therapy can be used to
prevent occurrences and perhaps
transmission.
– Women who acquire genital herpes during
pregnancy can transmit the virus to their babies.
– Untreated HSV infection in newborns can result
in mental retardation and death.
STIs
• AIDS (acquired immunodeficiency syndrome)
• First reported in the United States in1981.
• It is caused by the human immunodeficiency virus
(HIV),
– a virus that destroys the body's ability to fight off
infection.
• An estimated 900,000 people in the United States
are currently infected with HIV.
• People who have AIDS are very susceptible to many
life-threatening diseases (called opportunistic
infections) and to certain forms of cancer.
• Transmission of the virus primarily occurs during
sexual activity and by sharing needles used to inject
intravenous drugs.
STIs
•
Genital warts
– Caused by human papillomavirus,
• a virus related to the virus that causes common skin warts.
– Genital warts usually first appear as small, hard painless bumps
in the vaginal area, on the penis, or around the anus.
– If untreated, they may grow and develop a fleshy, cauliflowerlike appearance.
– Genital warts infect an estimated 1 million Americans each
year.
– In addition to genital warts, certain high-risk types of HPV
cause cervical cancer and other genital cancers.
– Genital warts are treated with a topical drug (applied to the
skin), by freezing, or if they recur, with injections of a type of
interferon.
– If the warts are very large, they can be removed by surgery.
STIs
• Genital herpes
– Affects an estimated 60 million Americans.
– Approximately 500,000 new cases of this
incurable viral infection develop annually.
– Caused by herpes simplex virus (HSV).
– painful blisters or open sores in the genital area.
– These may be preceded by a tingling or burning
sensation in the legs, buttocks, or genital region.
– The herpes sores usually disappear within two to
three weeks, but the virus remains in the body
for life and the lesions may recur from time to
time.
STIs
• Genital herpes
– Affects an estimated 60 million Americans.
– Approximately 500,000 new cases of this
incurable viral infection develop annually.
– Caused by herpes simplex virus (HSV).
– painful blisters or open sores in the genital area.
– These may be preceded by a tingling or burning
sensation in the legs, buttocks, or genital region.
– The herpes sores usually disappear within two to
three weeks, but the virus remains in the body
for life and the lesions may recur from time to
time.