Transcript Fetal Development

Blastocyst Development
• Zygote (fertilized egg) marks beginning of development
• Zygote develops into blastocyst
- Ball of cells
- ~ 5 days after fertilization
• Hormones (progesterone) released by corpus luteum
help zygote to develop and keep the uterine lining thick
Gastrula Development
• Blastocyst implants into
endometrium (lining of
uterus)
• Continues development
 Gastrula
–Ectoderm becomes skin &
nervous system
–Mesoderm becomes
muscles, blood, & internal
tissues
–Endoderm becomes
digestive & internal organs
Embryo Development
Blastocyst  Gastrula  Embryo
• Embryonic membranes protect & nourish embryo
• Endometrium becomes placenta
- Connects mother and embryo
• Umbilical cord develops
- Connects embryo to placenta
- Blood vessels from placenta to baby
• Mom’s & baby’s blood do not circulate
together!
• Can have 2 different blood types
• Nutrients move by diffusion
• Amniotic sac cushions embryo
- Amnion = membrane surrounding baby
- Amniotic fluid = “water” surrounding baby
• “water breaks” before baby is born
(membrane ruptures and fluid
escapes)
Fetal Development
Zygote  Blastocyst  Gastrula  Embryo  Fetus
• Fully formed fetus takes 38-40 weeks to develop
• Human pregnancies are divided into trimesters
Fetal Development
• First trimester (weeks 1-12):
- Body plan & early
development
• Heartbeat detected after
week 5
• Arms and legs begin to
develop
• Heart, brain, pancreas,
kidneys, liver begin to form
• Eyelids form then fuse for
iris to develop
• Hair, fingernails, and
toenails develop
• External sex organs show
sex of fetus (at end of
trimester)
Fetal Development
• Second trimester (weeks 13-27):
- Fetus more active & developed
• Most joints and bones have
started to form
• Skin is protected by fine air
and waxy substance
• Sleep cycles more regular
• Eyes open & blink
• Eyebrows/eyelashes form
• Fetus breathes amniotic
fluid (strengthens lungs)
• First movements felt by
mother
Fetal Development
• Third trimester (weeks 28-40):
- All organs fully form
• Fetus responds to light &
sound (from outside uterus)
• Fetus has periods of
dreaming
• Fine body hair thins, scalp
hair grows in
• Bones grow & harden
• Synapses between neurons
form in huge numbers
• Lungs complete
development
• Fetus turns head-down
(ready to exit)
Birth
• Baby is upside down
– Feet first = breech
position (not good)
• Cesarian-section (“Csection”)
• Labor
– Muscles help to thin &
open cervix
– Muscle contractions push
baby out
• After birth- placenta
detaches from uterus and
exits
The mother affects the fetus, and
pregnancy affects the mother.
• The fetus depends on the mother for all its
nutrition.
– mother's diet must support fetal health
– mother must avoid raw foods & toxic chemicals
• Pregnancy affects mother
– increase in Calories and body
weight
– pregnancy hormones affects
homeostasis
– regular medical checkups
needed
Review
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Define: blastocyst, gastrula, embryo
Explain the functions of the following:
Placenta
Umbilical cord
Amniotic sac
List at least 2 milestones for each trimester of pregnancy.
What might happen if the baby’s head is not upside down when ready for
birth?
Give 2 examples of how a mother and fetus affect one another.
Why might a pregnant woman need to be concerned about what she
eats and/or drinks?
A baby is born 12 weeks premature (early). The organs are developed,
but the baby must breathe using a ventilator. Explain why this might be
necessary.