2. 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

3. 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

4. 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)

5. Fetal Development Zygote  Blastocyst  Gastrula  Embryo  Fetus
Fully formed fetus takes weeks to develop
Human pregnancies are divided into trimesters

6. 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)

7. 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

8. 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)

9. Birth Baby is upside down Feet first = breech position (not good)
Cesarian-section (“C-section”)
Labor
Muscles help to thin & open cervix
Muscle contractions push baby out
After birth- placenta detaches from uterus and exits

11. 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

12. Pregnancy affects mother
increase in Calories and body weight
pregnancy hormones affects homeostasis
regular medical checkups needed

13. Review 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.