Pregnancy & Development
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Transcript Pregnancy & Development
Pregnancy & Development
Fertilization
Timing (egg “good for 12-24 hours; sperm
“good” for 48-72 hours)
Oviduct
Capacitation enables sperm to fertilize
ovum
Sperm numbers – about 50 “work” on the
egg
Fertilization
Diploid
Zygote
Sex determination
Twins
– Dizygotic (fraternal)
– Monozygotic (identical)
Cleavage
30 hours to 4 days
Mitosis
Oviduct
Morula
Blastocyst Stage
Day 5
Uterus
Rearrangement of cells
– Trophoblast cells will become placenta
– Inner cell mass will become fetus
Implantation – day 7 or 8
Gastrulation
Week 2
Ectoderm – destined to become nervous
tissue and skin
Mesoderm – destined to become skeleton,
muscles, heart, blood vessels…
Endoderm – destined to become gut &
lungs
Neurulation
Week 3
Embryo is 2mm long (pencil eraser size)
Neural groove
Neural tube
Destined to become brain and spinal cord
Organogenesis
Week 4
Embryo 5 mm long
All major organs have begun their
formation
Arm & Leg buds form
Thalidomide & German Measles examples
of what can go wrong.
Fetus
By end of third month, embryo is distinctly
human
All major organs are established
Growth for second and third trimester
Maintenance of Endometrium
Estrogen & Progesterone
From corpus luteum early
From placenta later
Birth control pills
Human Chorionic
Gonadotropin
HCG
Made by embryo
2-12 weeks
Maintains corpus luteum through first
trimester
Placenta
Development begins at 4 weeks and
functional by 12 weeks
Covers about 1/3 of inner uterus
Function
– Nutrients
– Waste
– Estrogen & Progesterone
Placenta
Maternal tissue
– Decidua basalis of the endometrium
Fetal tissue
– Chorion which develops from the trophoblast
cells
– Chorionic villi contain capillary beds from
umbilical arteries and vein
Fetal tissue
Umbilicus
Amnion
Amniotic fluid
Gestation
280 days
9 full months
Parturition
Mild contractions due to high levels of
estrogen.
Once contractions occur every 30 minutes,
labor occurs
Amniotic fluid released
Baby’s head serves as a “wedge”
Hormones
Estrogen increases which causes uterine
contractions, then levels drop as parturition
proceeds
Progesterone levels drop allowing the
uterine contractions
Local prostaglandins result in contractions
Hormones
Oxytocin causes strong uterine contractions
and works in a positive feedback
mechanism
Relaxin, made by placenta, dilates cervix,
relaxes symphysis pubis
Afterbirth
10-45 minutes later
Placenta