Lecture 17: Development II Flashcards
Morphogenesis
process by which animals takes shape
gastrulation
embryonic tissue layers
- reorganization of hollow blastula into gastrula
what are the embryonic germ tissue layers
ectoderm -> outer layer
endoderm > lines embryoynic digestive tract
mesoderm -> line between ecto & endo
` migration in sea urchin
mesenchyme cells migrate from vegetal ppole into blastocoel
invaginaton takes place at the
vegatol pole
filopodia in sea urchin
mesenchyme cells produce filopodia which extend toward blastocoel wall
contraction in sea urchin
filopodia contract and drag archenteron across blastocoel archenteron ( future digestive tube) forms from endodem cells
fusion in sea urchin
archenteron fuses with blastocoel wall
frog germ layers turn into
distinct set of stuructures
frog grastulation begins at
dorsal side of blastula at gray cresent ( opposite side of sperm entry)
what determines axis of development
sperm entry
invagination in frogs
- cells on dorsal side invaginate to form blastopore producing dorsal lip
involution in frogs
as a blastosphere forms , a sheet of cells spreads out of animal hemisphere ->
- rolls over dorsal lip & inward
- moves into interior
- forms endoderm and mesoderm
what is the second step of gastrulation in frogs
archenteron forms and blastocoel shrinks
3 germ layers in gastrulation
ectoderm - from cells remaining on surface
- endoderm - innermost layer
mesoderm - inbetween the two
blastocyst in humans consists of
- trophoblast - outer layer of cell
- inner cell mass
- blastocoel - central cavity
blostocyst reaches uterus after
6 days after fertilization
what happens when the blastocyst implants
- trophoblast secretes enzymes
- erodes area of penetraion
- thickens and extends projections into endometrium
- 7 after fertilization
what layers are formed by the inner mass cells
hypoblast (inner)
epiblast (outer layer): embryo proper, source of embryonic stem cells
chorion
- sourronds embryo & all other membranes
amnion
- encloses embryo in fliud filed amniotic cavity
yolk sac
forms blood cells
allantois
incorperated into umbilical cord -> forms blood vessels
gastrulation in humans
- takes one week ( during 2nd and 3rd week)
involution of epiblast cells
- form primative streak -> start of gastrulation
- some epiblast cells form w mesoderm, some mix with hypoblast ( forms endodemr) , some remain on surface ( form ectoderm)
what are the 4 extraembryonic membranes
amnion, chorion, yolk sac, and allantois
seq steps of human embryonic development
- ovulation
- ferritization
- cleavages
- implantation
- gastrulation
organogenesis
- process of organ formation
- 1st time ebryo begins to incease in size
nervous system
1st system to develop in most vertebrate embryos
neurulation
neurala -> embryo at state where neurotization occurs
neurula
- embryo at stage when neurulation occurs
during neurulation
- cells from dorsal mesoderm form notochord
- induction
- neural plate
- neural tube develops into central nervous system
- birth defects
induction
- process by which certain cells stimulate differentiation of neighboring cells
what happens during induction
developing notochord sends signal to overlying ectoderm -> thickens and forms neural plate
neural plate
- embryonic region that becomes nervous system
- neural plate rolls up and forms neural tube -> chordate nerve chord is hollow
what are the two main parts of the central nervous system
anterior -> brain
remainder -> spinal chord
anencephaly
neural tube fails to fuse at anterior -> no forebrain
spina bifida
neural tube fails to fuse in posterior region
neural tube defect incidence decreases if
preggo woman gets adequate folic acid
neural crest cells ( cell migration)
- develops at the neural tube
- migrate in embryo
- variety of tissues : nerves, parts of teeth, skull bones
somites
- role in organizing segmented structure of vertebrate body
somites contribute to
formation of serially repeating structures
ex: vertebrae, ribs, associated muscles
1st trimester ( 3 months)
- implanted embryo secrets human chorionic gonadotropin (hCG)
- main process of organogenesis
(hCG)
- Functions like LH from ant pit
- maintains secretion of Progesterone’s and estradione
what happens during the first 2-4 weeks of first trimester
- embryo obtains nutrients directly from endometrium
what happens with the trophoblast during the first trimester
mixes with endometrium -> forms placenta
placenta
- organ of exchange between mother and embryo
- provides nutrients and oxygen for fetus
- removes waste -> excreted by mother
umbilical cord
- connects embryo to placenta
what sometimes splits during the first month
- inner cell mass
- 2 groups of cells which develop independently
- if mass doesn’t separate completely = conjoined twins
fraternal twins
- result from release & fertilization of two eggs = generally distinct
at 8 weeks
all major structures have formed: embryo is a fetus
end of first trimester
- 2 inches long & weighs 1/2 oz
2nd trimester ( 4-6)
- fetus grows - uterus grows
- can tell ur preggo
- fetus is active
3rd trimester (7-9)
- rapid growth and final differentiation of tissues and organs
premature
birth before 37 weeks
postnatal care in mammals
- lactation
