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PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
3
HUMAN
ANATOMY
PART 1
Basic
Embryology
fifth edition
MARIEB | MALLATT | WILHELM
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
Embryology
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Embryology – study of the origin and
development of single individual
Prenatal period
 Embryonic period – first 8 weeks
 Fetal period – remaining 30 weeks
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Embryonic Period
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.1 (1 of 2)
Fetal Period
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.1 (2 of 2)
The Basic Body Plan
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Skin – dermis and epidermis
Outer body wall – trunk muscles, ribs, vertebrae
Body cavity and digestive tube (inner tube)
Kidneys and gonads – deep to body wall
Limbs
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Basic Body Plan
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.2
The Embryonic Period

Week 1 – from zygote to blastocyst
 Conception – in lateral third of uterine tube
 Zygote (fertilized oocyte) moves toward the uterus
 Blastomeres – daughter cells formed from zygote
 Morula – solid cluster of 12–16 blastomeres
 “Mulberry”
 Blastocyst – fluid-filled structure – ~ 60 cells
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Embryonic Period

Stages of first week
 Zygote
 4-cell
 Morula
 Early blastocyst
 Late blastocyst (implants at this stage)
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Fertilization and the Events of the
First 6 Days of Development
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.3
Week 2 – The Two-Layered Embryo

Bilaminar embryonic disc – inner cell mass
divided into two sheets
 Epiblast and the hypoblast
 Together they make up the bilaminar embryonic disc
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Week 2 – The Two-Layered Embryo

Amniotic sac – formed by an extension of epiblast
 Outer membrane forms the amnion
 Inner membrane forms the amniotic sac cavity
 Filled with amniotic fluid
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Week 2 – The Two-Layered Embryo

Yolk sac – formed by an extension of hypoblast
 Digestive tube forms from yolk sac
 NOT a major source of nutrients for embryo
 Tissues around yolk sac
 Gives rise to earliest blood cells and blood vessels
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Implantation of the Blastocyst
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.4 (1 of 3)
Implantation of the Blastocyst
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.4 (2 of 3)
Implantation of the Blastocyst
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.4 (3 of 3)
Week 3 – The Three-Layered Embryo
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Primitive streak – raised groove on the dorsal
surface of the epiblast
Gastrulation – a process of invagination of
epiblast cells
 Begins at the primitive streak
 Forms the three primary germ layers
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Week 3 – The Three-Layered Embryo
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Three Germ Layers*
 Endoderm – formed from migrating cells that
replace the hypoblast
 Mesoderm – formed between epiblast and
endoderm
 Ectoderm – formed from epiblast cells that stay on
dorsal surface
*All layers derive from epiblast cells!
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Primitive Streak
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Figure 3.5e–h
The Notochord
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Primitive node – a swelling at one end of
primitive streak
 Notochord forms from primitive node and
endoderm
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Notochord – defines body axis
 Is the site of the future vertebral column
 Appears on day 16
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Formation of the Mesoderm and Notochord
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.6
Neurulation
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Neurulation – ectoderm starts forming brain and
spinal cord
 Neural plate – ectoderm in the dorsal midline
thickens
 Neural groove – ectoderm folds inward
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neurulation
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Neurulation (continued)
 Neural tube – a hollow tube pinches off into the
body
 Cranial part of the neural tube becomes the brain
 Maternal folic acid deficiency causes neural tube
defects
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neurulation
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Neural crest
 Cells originate from ectodermal cells
 Forms sensory nerve cells
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Induction
 Ability of one group of cells to influence
developmental direction of other cells
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Mesoderm Begins to Differentiate
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Somites – our first body segments
 Paraxial mesoderm
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Intermediate mesoderm – begins as a continuous
strip of tissue just lateral to the paraxial mesoderm
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Mesoderm Begins to Differentiate
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Lateral plate – most lateral part of the mesoderm
 Coelom – becomes serous body cavities
 Somatic mesoderm – apposed to the ectoderm
 Splanchnic mesoderm – apposed to the endoderm
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings