THEATER 10 Lecture Notes - Lecture 20: Lateral Plate Mesoderm, Primitive Streak, Intermediate Mesoderm
Course CodeTHEATER 10
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Week 4 -- Body Takes Shape
• Derivatives of Germ Layers
• Ectoderm forms
• Brain, spinal cord, and epidermis (outside layer of human body)
• Endoderm forms
• Inner epithelial lining of gut
• Respiratory tubes, digestive organs, and urinary bladders
• Mesoderm forms (very complicated)
• Intermediate mesoderm
• Somatic and splanchnic mesoderm
Prenatal Period -- time between conception (union of egg and sperm) & birth [divide into 2
1. Embryonic (first 8 weeks)
• All major organs in place & embryo [early form of body] starts looking like a
2. Fetal (remaining 30 weeks)
• Organs grow larger and more complex
Blastocyst - fertilized egg in 2nd phase of growth.
• Forms a large, hollow ball of cells w/ a fluid center to meet growing cellular restraints.
3 Layered Embryo
Layers in which all body tissues develop
1. Ectoderm 2. Mesoderm 3. Endoderm
Germ layer begins to form when primitive streak appears. Epiblast cells migrate to streak &
displace the cells to become endoderm… the 3 germ layers all derived from epiblast cells
Ectoderm (outside skin) [colored blue in pic above]
Outermost of the three layer
• Forms outside layer of skin (epidermis), brain, and spinal cord (central nervous
o Sweat glands, hair, nails, teeth, lens of eye.
• On dorsal surface
Mesoderm (middle skin) [colored red]
• Forms muscle , bone, and connective tissue
• Between epiblast and endoderm
Endoderm (inner skin) [colored yellow]
• Forms innermost lining of inner tube (epithelial lining)
o Linings of respiratory and digestive tracts, liver, pancreas.
Notocord - primitive beginning to backbone.
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