Anatomy I - Module 4 (Early stages of embryology)

Connecting stalk

Developing umbilical cord

What does inner cell mass become

Epiblast and Hypoblast
Bilaminar embryonic disk

Epiblast

Becomes embryo
Develops amniotic sac and cavity (Water that breaks and surrounds embryo)
Becomes 3 germ layers

Hypoblast

Extraembryonic membranes
Forms yolk sac

Gastrulation

Formation of the 3 germ layers
Day 13-14

What happens to epiblast during gastrulation

Elongates into oval shape
Cells multiply and thicken forming primitive streak

Primitive streak

Determines caudal/cephalic end
cephalic is away caudal is toward

What are the 3 layers

Endoderm
Mesoderm
Ectoderm

Endoderm

Cells that move through the primitive streak, pushing on hypoblast
Becomes digestive system, lungs

Mesoderm

Inbetween epiblast and endoderm
Forms bones, muscles, blood vessels

Ectoderm

Cells that don’t move through primitive streak
Becomes skin and nervous system
Outer layer

Notochord

Forms from mesoderm cells
Involved in induction to form neural plate
Looks like cylinder

Induction

Group of cells that send signals to other cells to develop a specific way
Notochord sends signal to ectoderm to form Neural plate

Oropharyngeal membrane

Cephalic end
Mouth opening

Cloacal membrane

Caudal end
Opening to anus

Formation of neural tube

Neural plate thickens and folds, forming neural folds and neural groove
Once 2 sides get close, merge and become neural crest (Skin layer)
Form neural crest cells (PNS (non controlled nerves))

Neural tube

Becomes brain and spinal cord and CNS

Somites

Formed from mesoderm
Becomes ribs, vertebral column, skeletal muscle