Download Figure 47.0 Human embryo

Fertilization
• Fertilization activates the egg
• Activation of the egg triggers
embryonic development
Acrosomal Reaction
• The acrosomal reaction occurs in
echinoderms Ex. sea urchins
• Receptors on the vitelline egg layer are
specific
• The reaction is the fast block to
polyspermy
• A depolarization of the membrane
stops other sperm from penetrating
The acrosomal and cortical reactions during
sea urchin fertilization
Timeline for the fertilization of sea urchin eggs
Activation of The Egg
• Increase in calcium also
triggers an increase in
metabolic reaction in the egg
• Artificial activation of egg can
occur by injecting calcium ions
A wave of Ca2+ release during the cortical
reaction
Mammalian Fertilization
• Most mammals show internal fertilization
• Sperm has to reach zona pellucida by
penetrating follicle cells
• An acrosomal reaction occurs and sperm
cell enters egg
• Zona pellucida hardens which blocks
polyspermy
• Centrosomes originate from sperm cell
• Chromosomes share a common spindle
during first mitotic division
Fertilization in Mammals
Early Embryonic Development
6 days
2 weeks
Figure 47.6 Cleavage in an echinoderm (sea urchin) embryo
Cross Section of a Frog Blastula
Cleavage
• Fast mitotic divisions without G1 and
G2 phases
• Results in smaller blastomeres
• Polar planes of division occur with
animal and vegetal poles
• Holoblastic cleavage is complete
division of eggs with little yolk ex:
frogs
• Meroblastic = incomplete division with
moderate amt of yolk ex: birds
Gastrulation in a Frog Embryo
Body Symmetry
Exhibit
cephalization
Bilateral Symmetry – body plan in
which only a single, imaginary line
can divide the body into two equal
halves; Ex: vertebrates
Radial Symmetry – body plan in
which body parts repeat around
the center of the body; Ex: sea stars
• Organisms without body cavities
are considered acoelomates
Body covering
(from ectoderm)
(c)
Tissuefilled region
(from
mesoderm)
Acoelomate. Acoelomates such as flatworms
lack a body cavity between the digestive tract
and outer body wall.
Digestive tract
(from endoderm)
Figure 32.8c
• A pseudocoelom
– Is a body cavity derived from
the blastocoel, rather than
from mesoderm
Body covering
(from ectoderm)
(b) Pseudocoelomate. Pseudocoelomates
such as nematodes have a body cavity only
partially lined by tissue derived from
mesoderm.
Figure 32.8b
Pseudocoelom
Digestive tract
(from ectoderm)
Muscle layer
(from
mesoderm)
• A true body cavity is called a
coelom and is derived from
mesoderm; these animals
are called coelomates
Coelom
(a) Coelomate. Coelomates such as
annelids have a true coelom, a body
cavity completely lined by tissue
derived from mesoderm.
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Figure 32.8a
Body covering
(from ectoderm)
Figure 32.7 A comparison of early development in protostomes and deuterostomes
Cleavage in a Frog Embryo
Sea urchin development, from single cell to
larva
The Establishment of the Body Axes and the
First Cleavage Plane in an Amphibian
Becomes Posterior
End
Becomes
Dorsal Side
Becomes
Anterior End
• Many different structures are
derived from the three embryonic
germ layers during organogenesis
ECTODERM
MESODERM
ENDODERM
p. 999
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• 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
Organogenesis
• Folding, splitting and clustering of
cells begins organogenesis
• Ectoderm rolls into neural tube
• Mesodermal blocks form somites
along axis of notochord:
–Gives rise to vertebrae and
muscles of backbone
• Neural plate folds into the neural
tube and becomes central nervous
system
• Chorion - gas
exchange and
waste storage,
lines the egg shell
• Allantois – gas
exchange and
waste storage
connects embryo
to chorion
• Yolk sac – food
storage vitelline
vessels embed into
the yolk
• Amnion –
protective fluid
filled sac
http://eng-sci.udmercy.edu/courses/bio123/Chapter49/Chick.html
Human Embryo
Brain
Heart
Organogenesis in a Frog Embryo
Cleavage, gastrulation, and early organogenesis in a chick embryo
Organogenesis in a Chick Embryo
About
Eye
56 Hours
Old
Forebrain
Blood
Vessels
Heart
Somites
Neural
Tube
The Development of Extraembryonic Membranes in a Chick
Early development of a human embryo and its extraembryonic membranes
24 Hour Chick Embryo
http://www.uoguelph.ca/zoology/devobio/210labs/24hrwm.htm
48 Hour Chick Embryo
http://www.uoguelph.ca/zoology/devobio/210labs/48hrwm1.htm
72 Hour Chick Embryo
http://www.uoguelph.ca/zoology/devobio/210labs/72hrwm.htm
http://www.bioscience.drexel.edu/Homepage/Spring2003/BIO%20268/Embryology/Chick/pages/C6_W006T.htm