PP19 Embryonic Development

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PP19Embryonic Development
Chapter 13 pg 284-296 ANS 3319Dr. Michael J.
FieldsUniversity of Florida
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Three Periods of Conceptus Development

• Cleavage - mitotic divisions without increase in
  cell mass (1 to 12 days).
• Differentiation - process in which cells form
  specific organs and formation of germ layers
  (starts day 12).
• Growth - growth of fetus, bones start to ossify
  (starts day 70).

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Zygote DevelopmentOviduct

• Cleavage - mitotic divisions of the fertilized
  ovum increase the number of blastomeres without
  an increase in mass.
• Blastomere - one of the cells formed in the
  segmentation of a fertilized ovum.
• Sensitive to high environmental temperatures.

Blastomere
Cleavage
Zygote 2-cell
Zygote 4-cell
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Two Cell Embryo Oviduct-Ampulla Hours after
sperm penetration Sow 12 14 Ewe 16 21 Cow 20
- 24
Blastomere
One to two cell embryo First 24 hours
Susceptible to heat stress
Zona Pellucida
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Zona Pellucida
Nucleus
Blastomere
Two Cell Embryo Oviduct-Ampulla
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2nd Polar Body
1st Polar Body
Zona Pellucida
Blastomere
Two Cell Embryo Oviduct-Ampulla
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Two Cell Embryo Oviduct-Ampulla
Blastomere
Zona Pellucida
Two to four cell embryo Additional 12 hours
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Morula DevelopmentUterus

• Morula (mulberry) - solid mass of Blastomeres.
  Cells become unequal in size.

Morula 32 64 cell embryo
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Morula Uterus
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Blastula DevelopmentUterus

• Blastula or Blastocyst - fluid-filled cavity
  surrounded with a layer of Blastomeres.

Zona Pellucida (clear layer) Blastomere
(cells) Blastocoele (hollow cavity)
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Blastula Uterus
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Blastula Uterus
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Superovulation Blastula Uterus
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Embryo Quality Grade
IETS Guidelines (1998)

• Grade 1 - Excellent or Good
• Individual blastomeres are uniform in size,
  color, and density. Symmetrical and spherical
  embryo mass.
• At least 85 of the cellular material should be
  in an intact, viable embryo mass.
• Grade 2 - Fair
• Moderate irregularities in overall shape of the
  embryo mass, or size, color, and density of
  individual cells.
• At least 50 of the cellular material should
  be intact, viable embryo mass.
• Grade 3 - Poor
• Major irregularities in shape of the embryo
  mass, or size, color, and density of individual
  cells.
• At least 25 of the cellular material should
  be intact, viable embryo mass.

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Grade 1 8 cells No fragmentation Cells even
regular
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Grade 2 8 cells Slightly fragmented
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Grade 3 5 cells Moderate fragmentation Unevenly
sized blastomeres
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Grade 3 4 cells Severe fragmentation Unevenly
sized blastomeres
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Grade 3 2 cells Severe fragmentation Very poor
quality
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Blastula DevelopmentUterus

• Blastocyst flattens against the Zona Pellucida.
• Trophoblast layer forms nourishes embryo and
  forms extra-embryonic membranes (Placenta)
• Blastocyst also forms Inner Cell Mass.
• Forms the Embryonic Disc that eventually becomes
  the embryo (Embryo Proper).
• Stem Cells come from Inner Cell mass.

Inner Cell Mass Embryonic Disc Trophoblast
Placenta
Before Hatching Blastocyst expands and compacts
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Gastrula DevelopmentDay 7- 8

• Trophoblasts become more organized and turn into
  Ectoderm (forms epidermis and neural tissue) and
  extra-embryonic membranes (placenta).
• Inner Cell Mass - differentiates to Ectoderm,
  Mesoderm and the Embryonic Disc (embryo proper).
• Endoderm - layer of cells forming on the
  underside of the inner cell mass which spreads to
  line the blastocyst.

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IETS Guidelines (1998)
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Time Line
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Hatching Uterus Day 8
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Hatched Embryos

• Developed to an expanded blastocyst and hatched
  from the Zona Pellucida (Stage 8 or 9)

Blastocyst
ZP
Jousan
Hatching Blastocyst
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Pig Conceptuses Day 11
Tubular
Spherical
Kowalski
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Blastula
Morula
Inner Cell Mass
Conceptus
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Time Line of Development