Transcript Week 17-18 notesx

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 (“enzymeloaded” 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 (“enzymeloaded” 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
• Chorion
–Outermost membrane
• Part of the placenta
• Secretes HCG
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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
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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.
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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.
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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."
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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.
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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
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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
You need to know which STIs are
bacterial (and therefore curable
through antibiotics) and viral
(uncurable)
Virus
Bacteria
HPV (human papilloma virus) – Can
cause genital warts, some strains can
lead to genital cancers
Chlamydia
Herpes
Gonorrhea
HIV (Human immunodefficiency virus)
– Can develop into AIDS
Syphilis
This website has more information on STIs and sexual health