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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
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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
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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

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
3
HUMAN
ANATOMY
PART 2
Basic
Embryology
fifth edition
MARIEB | MALLATT | WILHELM
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
Changes in the Embryo
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.7a, b
Changes in the Embryo
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.7c, d
Week 4 – The Body Takes Shape

Folding of embryo laterally and at the head and
tail
 Embryonic disc bulges; growing faster than yolk
sac
 “Tadpole shape” by day 24 after conception
 Primitive gut – encloses tubular part of the yolk
sac
 Site of future digestive tube and respiratory
structures
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Week 4 – The Body Takes Shape
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.8
Week 4 – The Body Takes Shape
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Derivatives of the germ layers
 Ectoderm forms
 Brain, spinal cord, and epidermis
 Endoderm forms
 Inner epithelial lining of the gut tube
 Respiratory tubes, digestive organs, and urinary
bladder
 Notochord – gives rise to nucleus pulposus within
intervertebral discs
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Week 4 – The Body Takes Shape
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Mesoderm – forms
 Muscle
 Bone
 Dermis
 Connective tissues (all)

Mesoderm differentiates further and is more
complex than the other two layers
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Derivatives of Germ Layers
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.10
Week 4 – The Body Takes Shape
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Mesoderm (continued)
 Somites divides into
 Sclerotome
 Dermatome
 Myotome
 Intermediate mesoderm forms
 Kidneys and gonads
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Week 4 – The Body Takes Shape

Mesoderm (continued)
 Splanchnic mesoderm
 Forms musculature, connective tissues, and serosa
of the digestive and respiratory structures
 Forms heart and most blood vessels
 Somatic mesoderm – forms
 Dermis of skin
 Bones
 Ligaments
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
3
HUMAN
ANATOMY
PART 3
Basic
Embryology
fifth edition
MARIEB | MALLATT | WILHELM
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
The Germ Layers in Week Four
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.9a–d
Week 5-8 – The Second Month of Embryonic Development
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Limb buds form
Embryo first looks recognizably human (week 8)
Head is disproportionately large
All major organs are in place
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.11
The Fetal Period
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PLAY
A time of maturation and rapid growth
Cells are differentiating during the first half of the
fetal period
Normal births occur 38 weeks after conception
Premature birth is one that occurs before 38 weeks
Ultrasound of Fetus
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Developmental Events of the Fetal Period
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Table 3.1 (1 of 3)
Developmental Events of the Fetal Period
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Table 3.1 (2 of 3)
Developmental Events of the Fetal Period
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Table 3.1 (3 of 3)