PP7 Early Embryonic Growth II

1
PP7Early Embryonic Growth II

• Chapter 3 pg 43-62
• ANS 3043
• University of Florida
• Dr. Michael J. Fields

2
Inner Cell Mass

• Compact cell mass that pushes into blastocoele
  and eventually forms embryo proper
• Forms from rapid cell proliferation from one side
  of blastocyst called Posterior Marginal Zone
• Cell Mass migrates across blastocyst to form Area
  Pellucida (Area of Transparency)

3
Inner Cell Mass

• Embryo Develops from part of Inner Cell Mass
  known as Embryonic Disc
• Two layers
• Epiblast origin of animal tissues
• (Epi outside Blast blastomere cells)
• Hypoblast participtes in formation of
  extraembryonic membranes (Yolk Sac)

4
Gastrulation

• Cell Layer Formation
• Regions of embryo exert more control over
  development than individual cells controlling
  their own fate
• Cellular autonomy regions are developing rather
  than individual cells
• Cellular reorganization and movement of epiblast
  cells
• Trophoblast forms the placenta

5
Will become inner cell mass or embryonic disc
Area Pellucida
Trophectoderm eventually becomes chorionic cells
6
Embryonic Disc
Epiblast cells proliferate and migrate into
Hensons Node forming a long streak Primitive
Streak
Forms Yolk Sac
7
Gastrulation

• Hensons Node Replication of epiblast cells at
  posterior end of embryo
• Allows epiblast cell migration into blastocoele
• Primitive Streak Forms on caudal end of
  embryonic disc
• Marks future longitudinal axis of embryo (60-75
  length becomes spinal cord)
• Cells migrate towards anterior (head) and
  posterior (tail) ends

8
Gastrulation

• Primitive Groove depression forms at dorsal
  aspects of primitive streak
• Epiblast cells migrate medially and ventrally
  into groove
• Cells migrate beneath epiblast layer and above
  hypoblast layer to form a three layered embryo
• Three Layered Cake
• Forms Ectoderm, Mesoderm, Endoderm

9
Epiblast Becomes Ectoderm Mesoderm Endoderm
Becomes Yolk Sac
Ectoderm
Mesoderm
Endoderm
Neural Tube Spinal Cord
Notochord
10
Head
Longitudinal Axis Primitive Streak disappears
11
Embryonic Germ Layer Specification
ECTODERM CNS Sense organs Mammary glands
Sweat glands Skin Hair Hooves
MESODERM Circulatory system Skeletal system
Muscle Reproductive system Kidneys Urinary
ducts
ENDODERM Digestive system Liver Lungs
Pancreas Thyroid gland Most other glands

12
Gastrulation

• Germ Layer Formation
• Division, Migration and Induction of cells
• Juxtaposition of cellular sheets
• Ecto
• Meso
• Endo
• Allows for cell and tissue differentiation due to
  cell to cell interactions (migration)

13
Neurulation

• Formation of spinal cord precursors
• Occurs simultaneously with gastrulation
• Neural tube and notochord earliest identifiable
  structures of spinal cord
• Neural Crest Cells cells on apex of primitive
  groove
• Non-neural ectoderm forms the epidermis of fetus
• Notochord believed to form the disc between the
  vertebrae

14
Two types of ectoderm

• Formation of spinal cord precursors, occurs
  simultaneous with gastrulation

• Continued development of primitive groove, ridges
  form and elevate
• Neural ectoderm - outermost cell layer of
  primitive groove
• Precursors to the neural tube due to convergence
  and fusion of ridges
• Notochord located ventral to neural tube
• Neural tube and notochord earliest identifiable
  structures of spinal cord

Primitive Groove
15
Cavities of Body
- Muscle
Verterbral Column/Skelton
______
_____
Ectoderm
Neural Tube Spinal Cord
Mesoderm
Endoderm
Notochord