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 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

Blastocyst  Gastrula  Embryo Embryo Development Embryonic membranes protect & nourish embryo Endometrium becomes placenta Placenta: provides oxygen & nutrients; removes waste Connects mother and embryo Umbilical cord develops Connects blood vessels from placenta to blood vessels of 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) Blastocyst  Gastrula  Embryo

Fetal Development Fully formed fetus takes 38-40 weeks to develop Zygote  Blastocyst  Gastrula  Embryo  Fetus Fully formed fetus takes 38-40 weeks to develop Human pregnancies are divided into trimesters

Fetal Development 1st 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 (at end of trimester)

Fetal Development 2nd trimester (weeks 13-27): Fetus more active & developed Most joints and bones have started to form Skin is protected by fine hair 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 3rd 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) Fetal Development

Birth Vaginal birth Baby is upside down Cesarean-section (C-section) Feet first = breech position (not good) Labor Muscles help to thin & open cervix Uterine contractions push baby out After birth: umbilical cord is cut; placenta detaches from uterus and exits

Health The fetus depends on the mother for 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 Define: blastocyst, 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.