Vertebrate Development
Chapter 51
From Biology
Raven & Johnson
7th Ed.
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Outline
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Stages of Development
Cell Cleavage Patterns (focus on mammalian)
Gastrulation
Developmental Process During Neurulation
How Cells Communicate During Development
Embryonic Development-Vertebrate Evolution
Extraembryonic Membranes
Human Trimesters
Birth and Postnatal Development
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Fertilization
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Penetration
– glycoprotein-digesting enzymes in
acrosome of sperm head
Activation
– events initiated by sperm penetration
 chromosomes in egg nucleus complete
second meiotic division
 triggers movement of egg cytoplasm
 sharp increase in metabolic activity
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Stages of Development
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Nuclei fusion
– The third stage of fertilization is fusion of
the entering sperm nucleus with the
haploid egg nucleus to form the diploid
nucleus.
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Cell Cleavage Patterns
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Initial cell division, cleavage, is not
accompanied by an increase in the overall
size of the embryo.
– morula - mass of 32 cells
 Each cell is a blastomere.
 eventually a blastula is formed
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Terminology of Stages of Development
ZYGOTE
MORULA
SOLID BALL
EMBRYO
BLASTULA
(BLASTOCYST
IN MAMMALS)
GASTRULA
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Cell Cleavage Patterns
(only need to know yellow vocab here)
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Primitive chordates
– holoblastic cleavage - egg contains little or
no yolk, and cleavage occurs throughout
the whole egg
Amphibians and advanced fish
– Eggs contain much more cytoplasmic yolk
in one hemisphere than the other.
 large cells containing a lot of yolk at one
pole, and a concentrated mass of small
cells with very little yolk at the other pole.
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Holoblastic Cleavage
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Cell Cleavage Patterns
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Reptiles and birds
– eggs composed almost entirely of yolk
– cleavage only occurs in polar cytoplasm
 meroblastic cleavage
Mammals
– contain very little yolk
– holoblastic cleavage
– inner cell mass forms developing embryo
– outer sphere, trophoblast, enters
endometrium
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Meroblastic Cleavage
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Cell Cleavage Patterns
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Blastula
– Each cell is in contact with a different set
of neighboring cells.
 Induction; ie: eye formation
 Cell signals (chemical messengers)
regulate gene transcription in
neighboring cells.
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Gastrulation
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Certain groups of cells invaginate and
involute from the surface of the blastula
during gastrulation.
– By the end of gastrulation, embryonic cells
have rearranged into three primary germ
layers:
 ectoderm
 mesoderm
 endoderm
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Gastrulation
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Gastrulation in primitive chordates
– surface of blastula invaginates into the
blastocoel
 eventually inward-moving wall pushes up
against the opposite side of the blastula
 produces embryo with two cell layers:
 outer ectoderm
 inner endoderm
 mesoderm forms later between the
ectoderm and endoderm
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Gastrulation in a Lancet (a non-vertebrate
chordate)
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Gastrulation
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Gastrulation in reptiles, birds, mammals
– no yolk separates two sides of embryo
 lower cell layer differentiates into
endoderm and upper layer into ectoderm
without cell movement
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Mammalian Gastrulation
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Developmental Processes During Neurulation
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Tissue differentiation begins with the
formation of the notochord and the hollow
dorsal nerve cord.
– neurulation
After the notochord has been laid down,
ectodermal cells above the notochord
invaginate, forming the neural groove down
the long axis of the embryo.
– edges move toward each other and fuse
creating neural tube
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Mammalian Neural Tube Formation
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INDUCTION
FORMATION OF THE EYE (pg 1093 Fig 51.16)
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1. Optic vesicle grows from embryonic brain, which
induces…
2. Lens vesicle forms from ectodermal cells, which
induces…
3. Optic vesicle to round into optic cup (most of
eyeball)
 **Induction is based on genes turning on. It is
influenced by where the cell is (and what
chemical messengers it contacts).
4. Lens vesicle separates from ectoderm
5. Inner layer of optic cup becomes retina
6. Lens becomes transparent
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Developmental Processes During Neurulation
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On either side of the developing notochord,
segmented blocks of mesoderm tissue
called somites form (segmentation).
– Ultimately, somites give rise to muscles,
vertebrae, and connective tissues.
 Mesoderm in the head region remains
connected as somitomeres and form
striated muscles of the face, jaws, and
throat.
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How Cells Communicate During Development
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Nature of development decisions
– Some cells become determined early in
development.
– At some stage, every cell’s fate becomes
fixed (commitment).
 not irreversible, but rarely reverses
under normal conditions
How is this related to stem cell research
(embryonic/ adult stem cells)?
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Fig 51.17
Chordates Vertebrates
Zygote
Lining of
respiratory
tract
Pharynx
Endoderm
Lining of
digestive
tract
Brain,spinal
cord,spinal
nerves
Blastula
Gastrula
Ectoderm
Dorsal
nerve
cord
Neural
crest
Gill arches,
Epidermis, skin,
sensory
Major
hair, epithelium,
ganglia,
glands
inner ear, lens
Schwann
Liver
of eye
Pancreas
cells,adrenal
Mesoderm
Notochord
medulla
Outer covering
Circulatory
Integuof internal
Heart
system
ments
organs
Vessels
Blood
Lining of
Skeleton
Gonads
Somites
thoracic and
Segmented
abdominal
muscles
Kidney
cavities
Dermis
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•
Go to Active Board Interactive
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Embryonic Development - Vertebrate Evolution
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Ontogeny recapitulates phylogeny
– Embryological development (ontogeny)
involves the same progression of changes
that have occurred during evolution
(phylogeny).
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Vertebrate Embryonic Development
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Extraembryonic Membranes
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Fluid-filled amniotic membrane an
adaptation to terrestrial life
– amniotic membrane an extraembryonic
membrane
 Extraembryonic membranes, later to
become fetal membranes, include the
amnion, chorion, yolk sac, and allantois.
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Extraembryonic Membranes
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First Trimester
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First trimester
– fourth week - organ development
 organogenesis
 most women not yet aware of
pregnancy
 Fetal Alcohol Syndrome
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First Trimester
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Second month - morphogenesis
– limbs assume adult shape
– major organs become evident
– embryo is about one inch in length
Third month - completion of development
– now referred to as fetus
 nervous system and sense organs
develop
 all major organs established
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Second and Third Trimesters
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Second trimester - growth
– bone formation occurs
– covered with fine hair (lanugo)
– by the end of the sixth month, baby is one
foot in length
Third trimester - pace of growth accelerates
– weight of fetus more than doubles
– most major nerve tracts formed within brain
– by end, fetus is able to survive on own
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Birth and Postnatal Development
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Uterus releases prostaglandins
– begin uterine contractions, but then
sensory feedback (positive) from the
uterus stimulates the release of oxytocin
from the mother’s pituitary gland
 rate of contraction increases to one
contraction every two or three minutes
 strong contractions, aided by the
mother’s pushing, expels the fetus
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Birth and Postnatal Development
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Nursing
– Milk production, lactation, occurs in the
alveoli of mammary glands when they are
stimulated by prolactin.
– milk secreted in alveolar ducts which are
surrounded by smooth muscle and lead to
the nipple
 first milk produced after birth called
colostrum - rich in maternal antibodies
 Milk synthesis begins about three days
following birth.
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Birth and Postnatal Development
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Postnatal development
– Babies typically double their birth weight
within a few months.
– Neuron production occurs for six months.
– allometric growth
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Summary
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Stages of Development
Cell Cleavage Patterns
Gastrulation
Developmental Process During Neurulation
How Cells Communicate During Development
Embryonic Development-Vertebrate Evolution
Extraembryonic Membranes
Human Trimesters
Birth and Postnatal Development
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