Post on 21-Jan-2016
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From Egg to Embryo
Pregnancy –
Conceptus –
Gestation period –
Preembryo –
Embryo –
Fetus –
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Relative Size of Human Conceptus
Figure 28.1
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Accomplishing Fertilization
The oocyte is viable for 12 to 24 hours
Sperm is viable 24 to 72 hours
For fertilization to occur, coitus must occur no more than:
Three days before ovulation
24 hours after ovulation
Fertilization – when a sperm fuses with an egg to form a zygote
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Blocks to Polyspermy
Only one sperm is allowed to penetrate the oocyte
Two mechanisms ensure monospermy
Fast block to polyspermy -
Slow block to polyspermy – zonal inhibiting proteins (ZIPs):
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Events Immediately Following Sperm Penetration
Figure 28.3
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Cleavage: From Zygote to Blastocyst
Figure 28.4
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Implantation of the Blastocyst
Figure 28.5a
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Implantation of the Blastocyst
Figure 28.5b
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Placentation
Figure 28.7a-c
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Placentation
Figure 28.7d
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Placentation
Figure 28.7f
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Ectopic Pregnancy
When embryonic mass implants someplace other than endometrium
Most often is tubular
In abdominal cavity must be delivered by cesarean section
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Maternal Serum Screen and Amniocentesis
Done after 16 – 17 weeks to detect fetal chromosomal abnormalities
Serum screen – looks for protein markers
Amniocentesis – more invasive
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Hormonal Changes During Pregnancy
Figure 28.6
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Parturition: Initiation of Labor
Estrogen reaches a peak during the last weeks of pregnancy causing myometrial weakness and irritability
Weak Braxton Hicks contractions may take place
As birth nears, oxytocin and prostaglandins cause uterine contractions
Emotional and physical stress:
Activates the hypothalamus
Sets up a positive feedback mechanism, releasing more oxytocin
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Parturition
Fetus becomes too large for uterus, triggers fetus anterior pituitary to release ACTH
ACTH acts on fetus adrenal cortex to produce cortisol,
Cortisol targets placenta
Inhibits its production of progesterone
Stimulates production of estrogen
Increases release of prostaglandins
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Parturition: Initiation of Labor
Figure 28.16