Download AP Embryology 2014 v2

Animal Development
Features Shared By Most Animals
• At early stages of development, all vertebrate embryos are
very similar
• Major stages of embryonic development are: fertilization,
cleavage, gastrulation, organogenesis
• The zygote undergoes a series of mitotic divisions known as
cleavage which produces a blastula (often takes the form of
a multicellular hollow ball) in most animals
• Gastrulation (involving the infolding of embryonic cells
forming concentric germ layers that become the various
tissues and organs as development continues ; the formation
of the two-layered, cup-shaped embryonic stage) occurs
after the blastula has formed; during this process the
embryonic forms of adult body tissues are produced
Development and Body Plan
Fertilized egg (one cell) → cleavage begins →
two cell stage → four cell stage → → → → →
→ Morula (latin for mulberry – solid ball of
embryonic cells) → Blastula "Blasted Out”
(ball of cells with fluid filled center called
blastocoel) → Gastrulation (folding in to form
"germ layers")
More Features Shared By Most Animals
• Highly differentiated body cells which are organized
into tissues, organs, and organ systems for such
specialized functions as digestion, internal transport
(circulation), gas exchange, movement,
coordination, excretion, and reproduction
• Nervous tissue (impulse conduction) and muscle
tissue (movement) are unique to animals
• Reproduction is typically sexual with flagellated
sperm fertilizing non-motile egg to form diploid
zygotes (a diploid stage dominates the life cycle)
AP Embryology
Crash Course in Animal Development
Bonus – Name Embryo “E”
Mature Sperm Anatomy
• The acrosome vesicle contains the enzymes required to
digest its way though the ovum wall.
• Haploid nuclei (n=23) containing the paternal chromosome
set
• The 'mid-section' of the sperm contains many mitochondria
which synthesis ATP to provide the energy for the
movement of the tails structure.
The Egg
• The haploid nuclei (arrested at
metaphase II ) sits inside a cell with a
large volume of cytoplasm (yolk).
• During follicle development unequal
division of the cell during meiosis
produces the 1st polar body that can be
seen outside the plasma membrane.
This will not develop.
• The Zona pellucida surrounds the
structure and is composed of
glycoproteins. With the cortical
granules they will be involved in the
acrosome reaction at fertilization.
• Around the outside are the follicular
cells.
Acrosome and Cortical Rxns
Fertilization:
• In all species the egg cells release a specific signal usually a
polypeptide that acts as a signal to the sperm cell to fertilize
the egg and not other cells.
• The signals appear to be species specific and are one
mechanism that prevents hybridization although this is
probably more important in aquatic species rather than
humans.
• Other important events include the restoration of the diploid
number (n+n=2n) and mechanisms that prevent polyspermy
Acrosome and Cortical Rxns
Fertilization of the human egg
(a) The cumulus is a thick loose grouping of cells in a gelatinous matrix.
The sperm cell must penetrate this mass to reach the zona pellucida, a
glycoprotein matrix surrounding the egg plasma membrane.
(b) Contact between the zona pellucida and proteins in the sperm cells
membrane trigger a the acrosome reaction.
(c) The acrosome vesicle fuses with the sperm plasma membrane and
releases enzymes that digest a path through the zona pellucida.
(d) The membrane of the sperm cell and the ovum fuse together. This
causes a release of Ca2+ from the endoplasmic reticulum.
(e) The cortical vesicle fuse with the plasma membrane releasing
enzymes that destroy the sperm binding proteins on the zona
pellucida. This prevents polyspermy. The release of Ca2+ also
activate meiosis and prepare the cell for completion of reduction
division , MII and cell division
The acrosomal and cortical reactions
Even More Features Shared By Most Animals
• The zygote undergoes a series of
mitotic divisions known as cleavage
which produces a blastula (often takes
the form of a multicellular hollow ball)
in most animals
Early embryonic development
The HOX Genes
1.
2.
3.
4.
The transformation of a zygote to an animal of specific
form depends on the controlled expression in the
developing embryo of special regulatory genes called
Hox genes.
These genes regulate the expression of other genes.
Many of these Hox genes contain common “modules”
of DNA sequences, called homeoboxes.
Only animals possess genes that are both homeoboxcontaining in structure and homeotic in function.
a.
All animals, from sponges to the most complex insects
and vertebrates have Hox genes, with the number of Hox
genes correlated with complexity of the animal’s
anatomy.
Three Germ Layers
A germ layer is a layer of cells during fetal
development that all have similar fates.
a. Ectoderm
1) covers the surface of an embryo
2)
•
Forms the nervous system and epidermis
i.e. the "attractoderm"- anything that would
attract you to someone else- skin, brain, nervous
tissue and sensory organs such as eyes etc.
Three Germ Layers
b)
Endoderm
1) innermost germ layer which lines the
archenteron (primitive gut)
2)
Forms the lining of the digestive and
respiratory systems, bladder lining, and
the liver
• i.e. the "endernal" organs and anything branching
off the digestive, respiratory system
Three Germ Layers
c. Mesoderm
1) located between the ectoderm and
endoderm in tripoblastic animals
2)
•
muscular, circulatory (vascular),
excretory (urogenital), skeleton,
connective tissue, etc.
i.e. the "means-o-derm"- the means of getting
from one place to another
The “Body Cavity”
• Fluid-filled cavity that forms within the mesoderm
of an animal is called a coelom
a.
a “true” body cavity is lined with a layer
of mesoderm surrounding both the inside
of the body wall and the internal organs
b.
The structure and development of the coelom is
an important character for recognizing major
groups of animals.
Differentiation and the Fate of Cells
Cytoplasmic Factors in Determining the Fate of Cells
Acoelomates
a.
Acoelomate - no body cavity is
present between the digestive tract
and the outer body wall
1) This area is filled with cells
Body plans of the bilaterally symmetrical organisms
Body plans of the bilaterally symmetrical organisms
Body plans of the bilaterally symmetrical organisms
Pseudocoelomates
b.
Pseudocoelomate - a fluid filled body
cavity separates the digestive tract and the
outer body wall
1)
The cavity (pseudocoelom) is not
completely lined with mesoderm
therefore considered a “false” cavity
Body plans of the bilaterally symmetrical organisms
Body plans of the bilaterally symmetrical organisms
Coelomates
c.
Coelomate - fluid-filled body cavity completely lined
with mesoderm (a true body cavity)
1)
The coelom separates the digestive tract
from the outer body wall
2)
Mesenteries (tissues) connect the inner
and outer mesoderm layers and suspend the
internal organs in the coelom
3)
fluid cushions the organs to prevent injury
4)
internal organs can grow and move
independently of the outer body wall
5)
serves as a hydrostatic skeleton in soft-bodied
coelomates such as earthworms
Body plans of the bilaterally symmetrical organisms
Body plans of the bilaterally symmetrical organisms
Body plans of the bilaterally symmetrical organisms
Body plans of the bilaterally symmetrical organisms
The “Body Cavity” –
A Comparative Look
Introduction to Animals
Crash Course in Animals Part 1
Crash Course in Animals Part 2
Protostome-Deuterostome
Dichotomy
Coelomate phyla can be
divided into two distinct
evolutionary lines,
protostomes and
deuterostomes
Protostome-Deuterostome
Dichotomy
Protostomes and Deuterostomes are
distinguished by developmental
differences which include cleavage
patterns, coelom formation and the fate
of the blastopore (first opening of the
archenteron which forms during
gastrulation)
A comparison of early development in protostomes and deuterostomes
A comparison of early development in protostomes and
deuterostomes - Coelomate phyla can be divided into two distinct
evolutionary lines, protostomes and deuterostomes
Protostomes
Deuterostomes
Major animal groups
mollusks, annelids,
arthropods
echinoderms and
chordates
Cleavage
spiral, fate is
determinate (fixed)
radial, fate is
indeterminate
Blastopore
becomes mouth
becomes anus
Coelom
mesoderm arises from paired mesodermal
cells near the
pouches form from the
blastopore, with
primitive gut wall;
splitting forming the they enlarge and fuse
coelom
to form the coelom
Introduction to Chordates
Crash Course to Chordates