Exercise 44

1
Exercise 44

• Survey of Embryonic Development

2
Objectives

• Fertilization, zygote, morula, blastocyst,
  gastrula, fetus, chorion, chorionic villi,
  placenta, amnion, yolk sac, umbilical cord
• Embryonic structures and functions

3
Fertilization

• Fusion of two haploid (1n) gametes, occurs in
  uterine tube usually within a day after ovulation
• Sperm
• Delivers paternal chromosomes to fertilization
  site
• Egg
• Provides all the cellular organelles,
  nourishment, genetic programming for development
  AND maternal chromosomes
• 2000x the volume of the sperm cell
• Secondary oocyte has been suspended in Metaphase
  II until now

Fig. 29-1
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Zygote

• Product of fertilization (union of gametes)
• Contains 46 chromosomes (normal for a somatic
  cell)

Fig. 29-1
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Prenatal Development Atlas Diagrams

• 1st trimester
• Embryological early fetal development
• Beginnings of organ systems appear
• 2nd trimester
• Organs and systems nearly complete
• 3rd trimester
• Rapid fetal growth
• Most organ systems functional

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Embryonic Development MORULA

• Day 3-4 of development/cleavage (cell divisions)
• Solid multicellular (gt 4-cell stage) ball
• Morula mulberry
• Reaches uterus on day 4

Fig. 29-2
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Embryonic Development BLASTOCYST

• Over next 2 days
• Hollow ball with inner cavity
• Outer cellular layer (trophoblast, provides
  nutrients)
• Inner layer of cells (clustered at one end, will
  form the embryo)
• Implants in uterine wall

Fig. 29-2
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Embryonic Development GASTRULA

• Day 12
• Third layer formscells on surface migrate to
  central line primitive streak
• Migrating cells move between the 2 layers
• Now have 3 embryonic layers
• Ectoderm
• Mesoderm
• Endoderm

Fig. 29-4
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Embryonic Germ Layers
Neural tissue

• Ectoderm
• Mesoderm
• Endoderm

Connective tissues
Epithelia glands
Muscle tissue
Fig. 29-4
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Embryo to Fetus

• Fetus
• Start of month 3 to delivery

Fig. 29-5
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Extra-embryonic membranes

• Yolk sac
• Endoderm mesoderm
• Amnion
• Ectoderm mesoderm
• Allantois
• Endoderm mesoderm
• Chorion
• Mesoderm trophoblast

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Yolk sac

• Endoderm mesoderm
• Pouch
• Important site of blood cell formation

Fig. 29-5
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Amnion

• Ectoderm mesodermal cells form this two layered
  structure
• Enlarges throughout development
• Amniotic cavity contains amniotic fluid
• Surrounds, cushions developing embryo/fetus

Fig. 29-5
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Chorion

• Mesoderm and trophoblast cells form this vascular
  layer
• Provides transport of nutrients to the growing
  embryo/fetus (multicellular now, so diffusion
  alone wont suffice)
• Chorionic villi branches in contact with
  maternal tissues
• Embryonic blood vessels in each
• Supplies embryonic heart (beating by week 3)
• Gases and nutrients diffuse between embryonic and
  maternal circulationsno mixing of actual blood
  (separated by trophoblast)

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Chorion
Fig. 29-6
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Placenta

• Appearance of blood vessels in the chorion 1st
  step in creation of a functional placenta
• Temporary structure in uterine wall that allows
  the diffusion between fetal and maternal
  circulatory systems
• Fetal side
• Maternal side

Fig. 29-6
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Umbilical cord

• Connection between fetus and placenta
• Contains the allantois, placental blood vessels,
  yolk stalk of the yolk sac

Fig. 29-6
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Fig. 29-8
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Fig. 29-10
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Video

• The Miracle of Life