ch. 47 development Flashcards
when does a human embryo show development of distinctive features
5 weeks
fertilization
formation of diploid zygote from a haploid egg and sperm
events at egg surface during fertilization
- sperm penetrate protective layer around egg
- receptors on egg surface bind to molecules on sperm surface
- changes at egg surface prevent polyspermy
polyspermy
entry of multiple sperm nuclei into the egg
acrosomal reaction
acrosome at tip of sperm releases hydrolytic enzymes that digest material surrounding egg
when is acrosomal reaction triggered
when sperm meets the egg
fast block to polyspermy
gamete contact/fusion depolarizes egg cell membrane
what initiates the cortical reaction
fusion of egg and sperm
what happens during the cortical reaction seconds after the sperm binds to the egg
vesicles beneath egg plasma membrane release contents to form fertilization envelope
slow block to polyspermy
fertilization envelope
cortical reaction and fertilization envelope
- requires high concentration of Ca2+ in egg
- reaction triggered by change in Ca2+ concentration
- Ca2+ spread across egg correlates w/ appearance of fertilization envelope
what does the rise in Ca2+ in the cytosol of the egg increase
rates of cellular respiration and protein synthesis
how is egg activated
with the rapid changes in metabolism
where are the proteins and mRNAs needed for egg activation
already present in the egg
where is fertilization in mammals and other terrestrial animals
internal
what must sperm travel through to reach zona pellucida
layer of follicle cells surrounding egg
zona pellucida
extracellular matrix of egg
what does sperm binding trigger
cortical reaction
when does first cell division occur in mammals
12-36 hours after sperm binding
what is fertilization followed by
cleavage
cleavage
period of rapid cell division without growth
what does cleavage partition the cytoplasm of a large cell into
many smaller cells called blastomeres
blastula
ball of cells w/ fluid-filled cavity called a blastocoel
cleavage pattern in frogs and many other land animals
asymmetric due to distribution of yolk
yolk
stored nutrients
2 poles of cleavage pattern
- vegetal
- animal
vegetal pole
has more yolk
animal pole
has less yolk
cleavage furrows in frog
- first 2: form 4 equally sized blastomeres
- third: asymmetric due to yolk in vegetal hemisphere, unequally-sized blastomeres
holoblastic cleavage
complete division of the egg
- in species whose eggs have little or moderate amounts of yolk
- sea urchins and frogs
mesoblastic cleavage
incomplete division of the egg
- in species with yolk-rich eggs
- reptiles and birds
cleavage in Drosophila and other insects
multiple rounds of mitosis w/o cytokinesis
morphogenesis
process by which cells occupy their appropriate locations
what does morphogenesis involve
- gastrulation
- organogenesis
gastrulation
rearranges cells of blastula into a 3-layered embryo called a gastrula
3 layers produced by gastrulation
- ectoderm
- endoderm
- mesoderm
ectoderm
forms outer layers, for frogs:
- epidermis of skin and derivatives
- nervous/sensory systems
- pituitary gland/adrenal medulla
- jaws/teeth
endoderm
lines digestive tract, for frogs:
- epithelial lining of digestive tract/organs, respiratory/excretory/reproductive tracts lining
- thymus, thyroid, parathyroid glands
mesoderm
partly fills space between endoderm and ectoderm, for frogs:
- skeletal/muscle systems
- circulatory/lymphatic systems
- excretory and reproductive systems
- dermis of skin
- adrenal cortex
frog gastrulation
- group of cells on dorsal side of blastula begin to invaginate
- cells move from embryo surface into embryo by involution
- cells become endoderm/mesoderm
- cells on surface form ectoderm
- newly formed cavity is archenteron
- archenteron opens through blastopore (anus)
what is chick embryo composed of prior to gastrulation
upper and lower layer: epiblast and hypoblast
what happens during gastrulation of chicks
- epiblast cells move toward midline of blastoderm and then into the embryo toward the yolk
- midline thickens to form primitive streak
- hypoblast cells contribute to sac that surrounds yolk and connection between yolk and embryo
yolk in human eggs
very little
human equivalent of blastula
blastocyst
inner cell mass
cluster of cells at one end of the blastocyst
trophoblast
outer epithelial layer of the blastocyst
- doesn’t contribute to embryo, instead initiates implantation
what happens after implantation
trophoblast continues to expand, set of extraembryonic membranes is formed
purpose of extraembryonic membranes
- enclose specialized structures outside of the embryo
- provide life-support system for further development of embryo
what does gastrulation involve in humans
inward movement from the epiblast through a primitive streak, similar to chick embryo
how long after fertilization does the blastocyst implant in humans
7 days
how long after fertilization do the extraembryonic membranes form in humans
10-11 days
how long after fertilization does the gastrulation occur in humans
13 days
4 extraembryonic membranes
amnion, chorion, yolk sac, allantois
reproduction outside of aqueous environments required development of
- shelled egg of birds, reptiles, and monotremes
- uterus of marsupial and eutherian mammals
what are embryos surrounded by
fluid in a sac called the amnion
- allows reproduction on dry land
amniotes
mammals, reptiles, and birds - embryos all in amnion
chorion
gas exchange
amnion
encloses amniotic fluid
yolk sac
encloses yolk
allantois
disposes of waste products and contributes to gas exchange
organogenesis
various regions of germ layers develop into rudimentary organs
neurulation
formation of brain and spinal cord in vertebrates
how does neurulation begin?
- cells from dorsal mesoderm form notochord
- signaling molecules secreted by notochord/tissues cause ectoderm above to form neural plate (induction)
notochord
rod extending along dorsal side of embryo
induction
when cells or tissues cause a developmental change in nearby cells
what does an inward curving of the neural plate form
neural tube
what does the neural tube become
central nervous system
what happens to the notochord before birth
disappears, but contributes to parts of the disks between vertebrae
4 families of cell adhesion molecules
- cadherin
- Ig family
- selectin
- integrin
where do neural crest cells develop
along neural tube of vertebrates and migrate in body to form parts of embryo
what parts of the embryo will neural crest cells form
nerves, parts of teeth, and skull bones
somites
blocks of mesoderm lateral to the notoochord
what do parts of somites dissociate to form?
mesenchyme cells, which form the vertebrae, ribs, and muscles associated with vertebral column
what is early organogenesis in the chick similar to
early organogenesis in the frog
- 3 days old, rudiments of major organs apparent
what are the pattern and appearance of organogenesis in invertebrates different from?
that in vertebrates
- mechanisms of organogenesis (neurulation) are similar
what are essential to movement and cell shape?
microtubules and microfilaments of cytoskeleton
common mechanism fro invaginating cell layer
reorganizing cytoskeleton (like contraction of actin filaments)
apoptosis
programmed cell death
what happens to extra neurons that are produced during embryonic development?
eliminated by apoptosis
what happens to tail of tadpole during metamorphosis
apoptosis
determination
refers to process by which a cell/group of cells become committed to particular fate
differentiation
refers to resulting specialization in structure and function
do cells in a multicellular organism have the same or different genome?
same - difference comes from expression of different sets of genes
