Fertilization and Development. Fertilization Fertilization of the Ovum occurs in the oviduct...
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Transcript of Fertilization and Development. Fertilization Fertilization of the Ovum occurs in the oviduct...
![Page 1: Fertilization and Development. Fertilization Fertilization of the Ovum occurs in the oviduct –Only one sperm allowed Electrical block Surface of ovum.](https://reader036.fdocuments.us/reader036/viewer/2022081503/56649cb45503460f94977ee1/html5/thumbnails/1.jpg)
Fertilization and Development
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Fertilization
Fertilization of the Ovum occurs in the oviduct– Only one sperm allowed
• Electrical block
• Surface of ovum altered
• Binding sites for sperm altered
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Development
Nuclei of sperm and ovum fuse to form the zygote– 1st division (mitosis) Occurs in oviduct 30 hrs
after fertilization
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Development
Cell division continues as mass moves through the oviduct to the uterus – a central hollow forms and fills with fluid– Now called a blastocyst
• Cells on inside develop into embryo• Outer cells develop into
supportive cells
– Identical Twins
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Implantation
On 6th day blastocyst breaks free of zona
Implantation blastocyst in uterine wall on day 7- 8
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Implantation
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Implantation
Endometrium is maintained – Human corionic gonadotropic hormone (HCG)
sectreted by outer cells (Chorion) of blastocyst to maintain corpus luteum
• LH levels remain high
• HCG used in pregnancy tests
– Corpus luteum maintains levels of estrogen and progesterone to maintain endometrium
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The Embryo
During implantation, the outer layer of cells of the blastocyst produces two membranes that surround, protect, and nourish the embryo – Chorion forms the placenta– Amnion forms amniotic sac
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Development
Considered an embryo after implantation is complete – Approx. 2 weeks from fertilization
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Chorion
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Amnion
Forms a fluid filled sac that insulates the embryo and fetus that protects from– Infection– Dehydration– Impact– Temperature changes
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Umbilical cord
Contains one vein and two arteries– vein carries nutrient and oxygen rich blood
to the fetus. – two arteries return blood containing waste
from fetal circulation back to the placenta. • It takes about 30 seconds for a blood cell to
make the round trip through the cord
– cord can be as long as 4 feet at birth.
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Prenatal Development
The in’s and then outs
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Prenatal development
Pregnancy usually last for approximately nine months
Divided into three trimestersFirst Trimester
– Fertilization to the end of the 3rd month– by second week – germ layers form
• Ectoderm, endoderm, and mesoderm
– At one month – size is only 7mm
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Prenatal development
First Trimester (Cont.)– Heart and brain have formed
• heart rate can be heard at 10 weeks with a special instrument called a Doppler
– Limb buds with fingers and toes present– Placenta begins developing– Considered fetus after 8th week– Movement occurs around 9th week
• Sucking reflex
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1st Trimester
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4 wks
8 wks
12 wks
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2nd Trimester
Fetus is 57 mm – 350 mm long recognizable body form
– Arms, hands, fingers, legs, feet and toes are fully formed
• Bone begins to replace cartilage
most of organs and tissues developed– Eyes are almost fully developed
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2nd Trimester
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16 wks 20 wks
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2nd Trimester
At the end of 16 wks: – Fetus is developing reflexes such as sucking and
swallowing – Sex is identifiable – Skin is bright pink, transparent and covered with soft,
downy hairAt the end of 20 wks:
– Mother begins to feel fetal movement – Internal organs are maturing – Eyebrows, eyelids and eyelashes appear
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At the end of 24 weeks:– Eyelids begin to part and eyes open
occasionally for short periods of time – Skin is covered with protective coating called
vernix – Fetus is able to hiccup
2nd Trimester
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3rd Trimester
Rapid growth– Fetus is 350 mm – 530 mm long– Body mass increases from 0.68 kg to 3.4 kg– Organs are maturing
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3rd Trimester
At the end of 7 months: – If born at this time, he/she will be considered a
premature baby and require special care– Taste buds have developed – Fat layers are forming – Skin is still wrinkled and red
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3rd Trimester
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3rd Trimester
At the end of 8 months: – Tremendous brain growth occurs at this time – Most body organs are now developed with the
exception of the lungs • Movements or "kicks" are strong enough to be
visible from the outside • Kidneys are mature • Skin is less wrinkled • Fingernails now extend beyond fingertips
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3rd Trimester
At the end of 9 months: – The lungs are mature – Baby is now fully developed and can survive
outside the mother's body • Skin is pink and smooth
• Baby settles down lower in the abdomen in preparation for birth and may seem less active
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Parturition (Birth)
Uterine contractions signal beginning of labor– Cervix thins and begins to dilate (max. 10 cm)
– Labor starts when contractions are 10-15 min
Amniotic membrane is forced into birth canal– Often bursts and amniotic fluid lubricates the canal
(water breaking)
– Usually ruptures during delivery but may occur before
Contractions start moving baby through birth canal
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Parturition
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Hormones involved in birth
Relaxin– Produced by placenta causes ligaments in
pelvis to loosen
Oxytocin – positive feedback loop enhances strength of
contractions– Prostaglandins also involved
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Hormones involved in birth
Milk Production– Prolactin
• Levels increase dramatically after birth occurs
• estrogen & progesterone levels drop
• Stimulates glands in the breasts to produce fluids 1.5 L/day
– Oxytocin• Stimulates contractions that move milk into ducts
• Also causes contractions of sm. Muscle in uterus to return to normal size