Transcript Document

PowerPoint® Lecture Slide Presentation by Vince Austin
Human Anatomy & Physiology
FIFTH EDITION
Elaine N. Marieb
Chapter 29
Pregnancy and Human
Development
Part B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Placentation
• Formation of the placenta from:
• Embryonic trophoblastic tissues
• Maternal endometrial tissues
• The chorion develops fingerlike villi, which:
• Become vascularized
• Extend to the embryo as umbilical arteries and veins
• Lie immersed in maternal blood
• Decidua basalis – part of the endometrium that lies
between the chorionic villi and the stratum basalis
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Placentation
• Decidua capsularis – part of the endometrium
surrounding the uterine cavity face of the implanted
embryo
• The placenta is fully formed and functional by the
end of the third month
• Embryonic placental barriers include:
• The chorionic villi
• The endothelium of embryonic capillaries
• The placenta also secretes other hormones – human
placental lactogen, human chorionic thyrotropin, and
relaxin
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Placentation
Figure 29.7a-c
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Gem Layers
• The blastocyst develops into a gastrula with three
primary germ layers: ectoderm, endoderm, and
mesoderm
• Before becoming three-layered, the inner cell mass
subdivides into the upper epiblast and lower
hypoblast
• These layers form two of the four embryonic
membranes
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Embryonic Membranes
• Amnion – epiblast cells form a transparent
membrane filled with amniotic fluid
• Provides a buoyant environment that protects the
embryo
• Helps maintain a constant homeostatic temperature
• Amniotic fluid comes from maternal blood, and
later, fetal urine
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Embryonic Membranes
• Yolk sac – hypoblast cells that form a sac on the
ventral surface of the embryo
• Forms part of the digestive tube
• Produces earliest blood cells and vessels
• Is the source of primordial germ cells
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Embryonic Membranes
• Allantois – a small outpocketing at the caudal end of
the yolk sac
• Structural base for the umbilical cord
• Becomes part of the urinary bladder
• Chorion – helps form the placenta
• Encloses the embryonic body and all other
membranes
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Gastrulation
• During the 3rd week, the two-layered embryonic disc
becomes a three-layered embryo
• The primary germ layers are ectoderm, mesoderm,
and endoderm
• Primitive streak – raised dorsal groove that
establishes the longitudinal axis of the embryo
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Gastrulation
• As cells begin to migrate:
• The first cells that enter the groove form the
endoderm
• The cells that follow push laterally between the
cells forming the mesoderm
• The cells that remain on the embryo’s dorsal surface
form the ectoderm
• Notochord – rod of mesodermal cells that serves as
axial support
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Primary Germ Layers
• Serve as primitive tissues from which all body organs
will be derived
• Ectoderm – forms structures of the nervous system
and skin epidermis
• Endoderm – forms epithelial linings of the digestive,
respiratory, and urogenital systems
• Mesoderm – forms all other tissues
• Endoderm and ectoderm are securely joined and are
considered epithelia
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Primary Germ Layers
Figure 29.8a-e
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Primary Germ Layers
Figure 29.8f-h
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Organogenesis
• Gastrulation sets the stage for organogenesis,
formation of body organs
• By the 8th week all organ systems are recognizable
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Specialization of Ectoderm
• Neurulation – the first event of organogenesis gives
rise to the brain and spinal cord
• Ectoderm over the notochord thickens, forming the
neural plate
• The neural plate folds inward as a neural groove with
prominent neural folds
• By the 22nd day, neural folds fuse into a neural tube,
which pinches off into the body
• The anterior end becomes the brain; the rest becomes
the spinal cord
• Associated neural crest cells give rise to cranial,
spinal, and sympathetic ganglia
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Specialization of Ectoderm
Figure 29.9a, b
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Specialization of Ectoderm
Figure 29.9c, d
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