ANIMAL
DEVELOPMENT
1
CH 47 FERTILIZATION THROUGH
ORGANOGENESIS
STAGES OF HUMAN
DEVELOPMENT
1.
Fertilization
1. Zona pellucida
2. First cell division
2. Cleavage
1. Blastomere
2. Holoblastic cleavage
3. Meroblastic cleavage
4. regulation
3. Morophogenesis
Gastrulation
Organogenesis
2
1.
2.
FERTILIZATION
Female secretions increase sperm motility and change
structure to cause fertilization potential (capacitation)
Moist environment necessary for sperm
3
First six hours
FERTILIZATION
Zona pellucida contain receptor cite and acrosomal reaction
which binds sperm to egg
Changes cause slow polyspermy to prevent additional sperm
from entering egg
4
No fast polyspermy reactions in mammals
FIGURE 47.5
Zona pellucida
Follicle cell
Cortical
granules
5
Sperm
basal body
Sperm
nucleus
FERTILIZATION
First Cell Division
Mitosis forms true nuclei in daughter cells
12-36 hours after sperm bonding
Each cell is now a blastomere
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http://www.hhmi.org/biointeractive/human-embryonic-HHMI
embryonic development
CLEAVAGE
Rapid cell division with almost continuous S and M phases of
cell cycle
Little or no protein synthesis (G1 or G2)
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Blastula- Hollow ball of cells form with blastocoel cavity
FIGURE 47.6
50 m
(b) Four-cell stage (c) Early blastula
(d) Later blastula
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(a) Fertilized egg
CLEAVAGE
In frogs and mammals is holoblastic
“holo” means complete
Humans have 3 divisions in first three days with little yolk
forming
Birds and reptiles cleavage is meroblastic (incomplete) to get
extensive yolk formation
The “ends” of the blastula are called the animal pole and
vegetal pole
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Gray crescent is the area on the opposite side from sperm
binding
FIGURE 47.7
Zygote
2-cell
stage
forming
Gray crescent
0.25 mm
8-cell stage (viewed
from the animal pole)
4-cell
stage
forming
8-cell
stage
Animal
pole
0.25 mm
Blastula (at least 128 cells)
Blastula
(cross
section)
Blastocoel
10
Vegetal pole
REGULATION OF
CLEAVAGE
The total mass of the structure does not change from zygote
to blastula, the cells just get smaller
Cells divide until the ratio of material in each nucleus to
cytoplasm is sufficiently large
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Small cells balance the amount of DNA to mRNA for protein
synthesis (think surface are to volume ratio)
MORPHOGENESIS
Transformation of embryo orientation and shape
Important is the cell shape, position and survival
Two important phases:
1. Gastrulation- establishment of cell layers
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2. Organogenesis- formation of organs
MORPHOGENESIS:
GASTRULATION
During gastrulation there is a mass movement of cells which
results in the blastula becoming a gastrula
Three germ layers develop
ectoderm- outside layer
mesoderm- middle layer
endoderm- inside layer
Some organisms (cniderians) do not have a mesoderm
HHMI Differentiation and Cell Fate
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http://www.hhmi.org/biointeractive/differentiation-and-fatecells
FIGURE 47.8
ECTODERM (outer layer of embryo)
• Epidermis of skin and its derivatives (including sweat glands,
hair follicles)
• Nervous and sensory systems
• Pituitary gland, adrenal medulla
• Jaws and teeth
• Germ cells
MESODERM (middle layer of embryo)
• Skeletal and muscular systems
• Circulatory and lymphatic systems
• Excretory and reproductive systems (except germ cells)
• Dermis of skin
• Adrenal cortex
• Epithelial lining of digestive tract and associated organs
(liver, pancreas)
• Epithelial lining of respiratory, excretory, and reproductive tracts
and ducts
• Thymus, thyroid, and parathyroid glands
14
ENDODERM (inner layer of embryo)
FIGURE 47.9
Animal
pole
Blastocoel
Mesenchyme
cells
Gastrulation in
Sea Urchin
Vegetal plate
Vegetal
pole
Blastocoel
Filopodia
Mesenchyme
cells
Blastopore
Archenteron
50 m
Blastocoel
Ectoderm
Future ectoderm
Future mesoderm
Future endoderm
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
Blastopore
Digestive tube (endoderm)
Anus (from blastopore)
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Key
Archenteron
FIGURE 47.10
1
CROSS SECTION
SURFACE VIEW
Animal pole
Blastocoel
Gastrulation in
Frog
Dorsal
lip of
blastopore
Early
Vegetal pole
gastrula
Blastopore
Blastocoel
shrinking
2
3
Blastocoel
remnant
Dorsal
lip of
blastopore
Archenteron
Ectoderm
Mesoderm
Endoderm
Future ectoderm
Future mesoderm
Future endoderm
Late
gastrula
Blastopore
Blastopore
Yolk plug
Archenteron
16
Key
FIGURE 47.11
Fertilized egg
Primitive
streak
Gastrulation in
Chick
Embryo
Yolk
Primitive streak
Epiblast
Future
ectoderm
Blastocoel
Endoderm
Hypoblast
YOLK
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Migrating
cells
(mesoderm)
1 Blastocyst reaches uterus.
Gastrulation in
Human
Uterus
Endometrial epithelium
(uterine lining)
Inner cell mass
Trophoblast
Blastocoel
2 Blastocyst implants
(7 days after fertilization).
Expanding region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Trophoblast
3 Extraembryonic membranes
start to form (10–11 days),
and gastrulation begins
(13 days).
Expanding region of
trophoblast
Amniotic cavity
Epiblast
Hypoblast
Yolk sac (from hypoblast)
Extraembryonic mesoderm cells
(from epiblast)
Chorion (from trophoblast)
4 Gastrulation has produced a
three-layered embryo with
four extraembryonic
membranes.
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic mesoderm
Allantois
18
FIGURE 47.12
MORPHOGENESIS:
GASTRULATION IN HUMANS
1. Blastocyst first 6 days
Fertilization occurs in the oviduct
Inner cell mass becomes the embryo which is the source for
stem cells
Inner cell mass
Little yolk (stored nutrients)
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Blastocyst reaches uterus.
MORPHOGENESIS:
GASTRULATION IN
HUMANS
2. Trophoblast 7 days after fertilization
Outer epithelium secretes enzymes for implantation which
allows for blood to surround trophoblast
Epiblast-upper layer becomes the embryo
Hypoblast- lower layer
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Maternal
blood
vessel
MORPHOGENESIS:
GASTRULATION IN HUMANS
3. Extraembryonic membranes 10-11 days
Formed by embryo
Enclose special structures outside the embryo
Gastrulation begins day 13 when implantation is complete
Cell migration occurs as cells move inward from epiblast
through primitive streak to form mesoderm and endoderm
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Chick gastrulation
FIGURE 47.12C
Expanding region of
trophoblast
Amniotic cavity
Epiblast
Hypoblast
Yolk sac (from hypoblast)
Extraembryonic mesoderm
cells (from epiblast)
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Chorion (from trophoblast)
3 Extraembryonic membranes
start to form (10–11 days),
and gastrulation begins
(13 days).
MORPHOGENESIS:
GASTRULATION IN HUMANS
4. End of gastrulation
Three germ layers are formed
Extraembryonic layers from placenta
23
These layers are an evolutionary necessity in land (dry)
environments
FIGURE 47.12D
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic mesoderm
Allantois
24
4 Gastrulation has produced a
three-layered embryo with
four extraembryonic
membranes.
ORGANOGENESIS
More localized changes
Spinal cord
Bones (or specific)
skin
heart
intestine
liver
Muscles (or specific)
eyes
ears
HHMI
25
Research
brain