GESTATION

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GESTATION

• Honors Biology

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Introduction

• Gestation is when sperm fertilizes an egg
• Results in a ZYGOTE
• How many chromosomes are in a zygote?
• In 9 months zygote ? trillions of cells

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FERTILIZATION

• Sperm
• Vagina ? cervix ? uterus ? fallopian tube
• 48 72 hours may encounter an egg from ovulation
• Head of sperm digests protective layer of egg
• Head of sperm and egg fuse together
• Egg membrane changes so no more can enter
• Haploid sperm (23 chromosomes) haploid egg (23
  chromosomes) diploid zygote (46 chromosomes)

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Cleavage and Implantation

• In tube the zygote begins MITOSIS (cleavage)
• Makes a ball of cells same size as zygote
  (MORULA)
• Makes a fluid filled BLASTOCYST
• Reaches uterus and implants in lining (thick)
  IMPLANTATION
• PREGNANT (6 days after fertilization)

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PREGNANCY

• First trimester
• Ball of cells ? 3 layers Differentiation
• Amnion forms makes amniotic sac
• Placenta nutrients, gases, drugs pass forom
  mother to fetus umbilical cord
• Blood never mixes diffusion
• HCG secreted to retain uterine lining (also
  progesterone and estrogen)

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PREGNANCY

• First Trimester
• Brain, spinal cord and nervous system by 3rd week
• Heart beats at 21 days
• Body plan developed
• 8 weeks ? birth fetus

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PREGNANCY

• Second Trimester
• Abdomen swells
• Uterus enlarges
• Hear heartbeat
• Wake and sleeps
• Movement
• Swallow, hiccup, suck thumb
• Eyes open

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PREGNANCY

• Third Trimester
• Fetus grows and gets ready to survive on the
  outside
• See light and dark
• React to sound
• Develops fat to
• insulate body

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CHILDBIRTH

• 270 days after fertilization
• Hormones stimulate childbirth
• Smooth muscles in uterus contract
• Amniotic sac breaks
• Muscles in vagina and cervix relax
• Contractions push fetus out of vagina
• Birth to afterbirth
• Soon respiratory and circulatory becomes own!

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