BIOL 223 Ch 47 Animal Development abbvphilipdarrenjones.com/.../biol...development_abbv.pdf · 3...
Transcript of BIOL 223 Ch 47 Animal Development abbvphilipdarrenjones.com/.../biol...development_abbv.pdf · 3...
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Chapter 47
Animal Development
BIOL 223
• Embryonic development
• determined by the zygote’s genome
• and molecules in the egg called
cytoplasmic determinants
• Cell differen2a2on
• specializaBon of cells in structure and
funcBon
• Morphogenesis
• process by which an animal takes
shape
Embryonic Development
Stages of embryonic development • Three stages of development
• Cleavage
• cell division creates a hollow ball of cells
• called a blastula
• Gastrula2on
• cells are rearranged into a three-‐layered gastrula
• Organogenesis
• the three layers interact and move to give rise to organs
• Due to posiBonal informaBon
PLAY
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FerBlizaBon
• FerBlizaBon
• brings the haploid nuclei of sperm and
egg together
• forming a diploid zygote
• The sperm’s contact with the egg’s surface
• iniBates metabolic reacBons in the egg
• that trigger the onset of
embryonic development
The Acrosomal ReacBon • Acrosome
• Structure at the Bp of the sperm
• releases hydrolyBc enzymes
• that digest material surrounding the egg
• acrosomal reac2on
• Gamete contact and/or fusion
• depolarizes the egg cell membrane
• sets up a fast block to polyspermy
• Not seen in mammals
• Charge inside of egg changes from negaBve to posiBve
The CorBcal ReacBon
• cor2cal reac2on
• induces a rise in Ca2+
• that sBmulates cor2cal granules
• to release their contents
outside the egg
• causes formaBon of a fer2liza2on
envelope
• that funcBons as a slow block to
polyspermy
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Fig. 47-3-5
Basal body (centriole)
Sperm head
Sperm-binding receptors
Acrosome Jelly coat Vitelline layer
Egg plasma membrane
Hydrolytic enzymes
Acrosomal process
Actin filament
Sperm nucleus
Sperm plasma membrane
Fused plasma membranes
Fertilization envelope
Cortical granule
Perivitelline space
EGG CYTOPLASM
AcBvaBon of the Egg
• sharp rise in Ca2+ in the egg’s cytosol
• increases the rates of cellular
respiraBon and protein
synthesis by the egg cell
• egg is now acBvated
• sperm nucleus merges with the egg
nucleus
• and cell division begins
Cleavage • cleavage
• a period of rapid cell division without growth
• parBBons the cytoplasm of one large cell
• into many smaller cells called blastomeres
• Morula
• Solid ball of cells (~4-‐32 cells)
• Blastula
• ball of cells with a fluid-‐filled cavity called a blastocoel
(a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula
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• The eggs and zygotes of many animals
• have a definite polarity
• except mammals
• Polarity defined by distribuBon of yolk (stored nutrients)
• vegetal pole has more yolk
• animal pole has less yolk
• three body axes
• established by the egg’s polarity
• and by a corBcal rotaBon following binding of the sperm
• CorBcal rotaBon
• exposes a gray crescent opposite to the point of sperm entry
Cleavage
Fig. 47-7
(a) The three axes of the fully developed embryo
(b) Establishing the axes
Pigmented cortex
Right
First cleavage
Dorsal
Left
Posterior
Ventral
Anterior
Gray crescent
Future dorsal side
Vegetal hemisphere
Vegetal pole
Animal pole Animal hemisphere
Point of sperm nucleus entry
Fig. 47-8-6
Blastula (cross section)
Blastocoel Animal pole
4-cell stage forming
2-cell stage forming
Zygote 8-cell stage
Vegetal pole
0.25 mm 0.25 mm
• Cleavage planes
• usually follow a paVern that is relaBve
• to the zygote’s animal and vegetal poles
Cleavage
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• Cell division is slowed by yolk
• Holoblas2c cleavage
• complete division of the egg
• occurs in species whose eggs have liVle or moderate amounts of yolk
• sea urchins and frogs
• As well as mammals
• Meroblas2c cleavage
• incomplete division of the egg
• occurs in species with yolk-‐rich eggs
• repBles and birds
Cleavage
GastrulaBon • Gastrula
• Three layered embryo with a primiBve gut
• Called germ layers
• Gastrula2on
• Process of making a gastrula
• rearranges the cells of a blastula
• Into the three layers
• embryonic germ layers
• ectoderm forms the outer layer
• endoderm lines the digesBve tract
• mesoderm partly fills the space between the endoderm and ectoderm
• GastrulaBon in the frog (holoblasBc cleavage)
• frog blastula is many cell layers thick
• Cells of the dorsal lip
• originate in the gray crescent
• and invaginate to create the archenteron
• Cells conBnue to move from the embryo surface
• into the embryo by involu2on
• These cells become the endoderm and mesoderm
• The blastopore
• encircles a yolk plug when gastrulaBon is completed
• The surface of the embryo is now ectoderm
• innermost layer is endoderm
• middle layer is mesoderm
Frog GastrulaBon
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Future ectoderm
Key
Future endoderm Future mesoderm
SURFACE VIEW
Animal pole
Vegetal pole Early gastrula
Blastopore
Blastocoel
Dorsal lip of blasto- pore
CROSS SECTION
Dorsal lip of blastopore
Late gastrula
Blastocoel shrinking Archenteron
Blastocoel remnant
Archenteron
Blastopore
Blastopore Yolk plug
Ectoderm Mesoderm
Endoderm
• GastrulaBon in the chick (meroblasBc cleavage)
• The embryo forms from a blastoderm
• And sits on top of a large yolk mass
• upper layer of the blastoderm (epiblast)
• moves toward the midline of the blastoderm
• and then into the embryo toward the yolk
• primi2ve streak
• Thickening midline
• movement of different epiblast cells
• gives rise to the endoderm, mesoderm, and ectoderm
Chick GastrulaBon
Fig. 47-11
Endoderm
Future ectoderm
Migrating cells (mesoderm)
Hypoblast
Dorsal Fertilized egg
Blastocoel
YOLK
Anterior
Right
Ventral
Posterior
Left
Epiblast
Primitive streak
Embryo
Yolk
Primitive streak
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Organogenesis (NeurulaBon) • organogenesis
• various regions of the germ layers
• develop into rudimentary organs
• Early in vertebrate organogenesis
• the notochord forms from mesoderm
• and the neural plate forms from ectoderm
• neural plate soon curves inward
• forming the neural tube
• will become the central nervous system
• Neural crest cells
• develop along the neural tube of vertebrates
• and form various parts of the embryo (nerves, parts of teeth, skull bones, and so on)
• Mesoderm lateral to the notochord forms blocks called somites
• Lateral to the somites, the mesoderm splits to form the coelom
Fig. 47-12
Neural folds Tail bud
Neural tube
(b) Neural tube formation
Neural fold
Neural plate
Neural fold
Neural plate
Neural crest cells
Neural crest cells
Outer layer of ectoderm Mesoderm
Notochord
Archenteron
Ectoderm
Endoderm
(a) Neural plate formation
(c) Somites
Neural tube
Coelom
Notochord
1 mm 1 mm SEM
Somite
Neural crest cells
Archenteron (digestive cavity)
Somites Eye
ECTODERM MESODERM ENDODERM
Epidermis of skin and its derivatives (including sweat glands, hair follicles) Epithelial lining of mouth and anus Cornea and lens of eye Nervous system Sensory receptors in epidermis Adrenal medulla Tooth enamel Epithelium of pineal and pituitary glands
Notochord Skeletal system Muscular system Muscular layer of stomach and intestine Excretory system Circulatory and lymphatic systems Reproductive system (except germ cells) Dermis of skin Lining of body cavity Adrenal cortex
Epithelial lining of digestive tract Epithelial lining of respiratory system Lining of urethra, urinary bladder, and reproductive system Liver Pancreas Thymus Thyroid and parathyroid glands
DerivaBves of Embryonic Germ Layers
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Developmental AdaptaBons of Amniotes
Embryo
Amnion
Amniotic cavity with amniotic fluid
Shell
Chorion
Yolk sac
Yolk (nutrients)
Allantois
Albumen
• Amniotes
• Embryos of birds, other repBles, and mammals
• develop in a fluid-‐filled sac in a shell or the uterus
• four extraembryonic membranes form around the embryo:
• chorion
• funcBons in gas exchange
• Contributes to the placenta in mammals
• amnion
• encloses the amnioBc fluid
• yolk sac
• encloses the yolk
• allantois
• disposes of waste products and contributes to gas exchange
Mammalian Development • The eggs of placental mammals
• Are small and store few nutrients
• Exhibit holoblasBc cleavage
• Show no obvious polarity
• GastrulaBon and organogenesis
• resemble the processes in birds
• and other repBles
• Early cleavage
• is relaBvely slow in humans and other mammals
• Blastocyst
• Formed at compleBon of cleavage
• inner cell mass
• Inside blasotcoel
• A group of cells develops into embryo
• and forms the extra-‐embryonic membranes
• trophoblast
• outer epithelium of the blastocyst
• iniBates implantaBon in the uterus
• and the inner cell mass of the blastocyst forms a flat disk of cells
• As implantaBon is completed
• gastrulaBon begins
Mammalian Development
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Fig. 47-16-1
Blastocoel
Trophoblast
Uterus
Endometrial epithelium (uterine lining)
Inner cell mass
Fig. 47-16-2
Trophoblast
Hypoblast
Maternal blood vessel
Expanding region of trophoblast
Epiblast
• epiblast cells
• invaginate through a primiBve streak
• to form mesoderm and endoderm
• Placenta
• allows for the exchange of materials
• between the mother and embryo
• is formed from the trophoblast
• mesodermal cells from the epiblast
• and adjacent endometrial Bssue
• By the end of gastrulaBon
• the embryonic germ layers have formed
Mammalian Development
Yolk sac (from hypoblast)
Hypoblast
Expanding region of trophoblast Amniotic cavity Epiblast
Extraembryonic mesoderm cells (from epiblast) Chorion (from trophoblast)
Yolk sac
Mesoderm
Amnion Chorion Ectoderm
Extraembryonic mesoderm Atlantois
Endoderm
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You should now be able to:
1. Describe the acrosomal reacBon
2. Describe the corBcal reacBon
3. DisBnguish among meroblasBc cleavage and holoblasBc cleavage
4. Compare the formaBon of a blastula and gastrulaBon in a sea urchin, a frog, and a chick
5. List and explain the funcBons of the extraembryonic membranes