Human Reproduction and Development Fertilization Pregnancy
Development Birth
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Human Reproduction and Development Sperm
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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
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3 Steps of Fertilization
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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Pregnancy Umbilical cord Contains: 2 fetal arteries Fetus to
placenta One fetal vein Placenta to fetus
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Pregnancy
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Childbirth Also called parturition 38 42 weeks from conception
Average = 40 weeks Three stages of childbirth 1.Labour 2.Delivery
3.Afterbirth
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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
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Childbirth 3.Afterbirth Immediately after delivery Blood
vessels in placenta contract Placenta separates from uterine wall
Expelled by muscle contractions
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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
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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
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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
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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
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Fetal Development A blastocyst embeds in the uterine wall
Consists of cells of the future embryo Surrounded by a sphere of
cells Embryonic membrane (extra- embryonic membrane) Support the
developing embryo
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Fetal Development Amnion Innermost embryonic membrane Next to
baby Fluid-filled sac that cushions the baby
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Fetal Development Umbilical cord Connection between mother and
baby Belly-button to placenta Carries babys blood to and from
placenta
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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
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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
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Gastrulation
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Human Gestation 1 st Trimester From fertilization to end of 3
rd month (0 13 weeks) Zygote begins cell division as it moves down
oviduct Becomes blastocyst and implants in uterus
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Human Gestation 1 st 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.
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Human Gestation 1 st 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
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Gastrulation
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6 weeks
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Gastrulation 7 weeks
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Gastrulation 8 Weeks
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8 weeks
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10 Weeks
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11 Weeks
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14 Weeks
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Human Gestation 2 nd Trimester Fetus grows rapidly To about 30
cm Quite active Hair begins to develop Cartilage of skeleton is
replaced by bone
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Gastrulation 18 weeks
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47 The Hand Picture May 2, 2000 USA Today
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48 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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49 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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50 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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51 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
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Human Gestation 3 rd 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
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Parturition
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Reproductive Technologies
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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