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Lecture 20

THEATER 10 Lecture Notes - Lecture 20: Lateral Plate Mesoderm, Primitive Streak, Intermediate Mesoderm

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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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