early fetal development Flashcards
when is fertilization age
measured from time of fertilization
when is gestational age
calculated from time of the beginning of the last menstrual period
determined by:
- fertilization day +14 days
- early ultrasound and compare to embryo charts
What is the Carnegie stage
23 stages of development of embryo- based on features not time
can compare development with other species
what is the embryogenic stage (14-16 days post fertilization)
what is the embryonic stage (16-50 days post fertilization)
what do these two stages both form
when two populations of cells are determined- pluripotent cells (contribute to fetus) and extraembryonic cells (contribute to support structures eg placenta)
when embryo is established from oocyte- morula just turned to blastocyst
establishment of germ layers and different tissues
first trimester
what is the fetal stage (50-270 days)
what stage is this part of
major organ systems are developed, migrate to final location
foetus viability established (survival outside the womb)
second trimester
what are the stages of embryo development, starting from oocyte
ovulated oocyte (1cell ) zygote (1 cell) cleavage stage embryo (2-8cell) Morula (16 cells) blastocyst (200-300cells)
what is the embryo dependant on to get through the first stage of divisions
when are they synthesised and stored
what happens when there is a failure to store or interpret these properly
Maternal mRNA and proteins
during oocyte development
impairs embryonic development
what happens during the maternal to zygotic transition
transcription of embryonic genes (zygotic genome activation)
inc. protein synthesis
organelle maturation
what happens past the 8 cell stage
compacted morula becomes blastocyst
spherical cells turn wedge shaped
outer cells pressed against zona and become polarised
formation of blastocyst cavity
how to outer cells connect to each other and how does this affect their connection to the inner cells
form tight gap junctions and desmosomes
form a barrier against diffusion to the inner cells
In a blastocyst, what is:
- zona pellucida
- inner cell mass
- trophoectoderm
- blastocoel
hard protein shell, protects embryo, prevents polyspermy
pluripotent embryonic cells contributing to foetus tissue
extraembryonic cells that contribute to support structures
fluid filled cavity osmotically formed due to trophectoderm pumping Na+ into cavity
why does blastocyst need to exit zona pellucida
how does this occur
to implant it into uterus
enzymatic digestion
cellular contraction
what does the trophectoderm split into
how do syncitiotrophoblasts form
what do syncitiotrophoblasts do
what do cytotrophoblasts do
syncitiotrophoblast and cytotrophoblast
by trophoblast cells fusing together
destroys local cells in endometrium of uterus
creates interface between embryo and maternal blood supply
provide source of syncitiotrophoblast cells
what does the inner cell layer split into
what is the function of each
epiblast and hypoblast
epiblast: form fetal tissue
hypoblast: form yolk sac (extraembryonic)
when does the bi laminar embryonic disc form
how does this form
what do amnion cells do
what do syncitiotrophoblasts secrete at this stage
day twelve
cells are separated from epiblast and form aminotic cavity
form extra embryonic membranes
HCG
Describe the process of gastrulation
a thickened structure forms along the midline of the epiblast called the primitive streak
the primitive streak expands at the cranial end forming the primitive node which has a circular depression inside called the primitive pit
the depression continues along the midline of the epiblast towards the caudal end forming the primitive groove
epiblast cells on top of the groove detach from epiblast and migrate towards groove, go inwards through the groove into the interior of the embryo- invagination
they displace hypoblast cells and form a new germ layer called the endoderm
the epiblast cells that didn’t migrate through the groove are called the ectoderm and the cells between the endoderm and ectoderm are called the mesoderm
what organs are derived from the endoderm
what organs are derived from the ectoderm
what organs are derived from the mesoderm
thyroid, lung, GI Tract, Liver, Pancreas
CNS, neural crest, skin epithelia, tooth enamel
bone, cartilage
blood (endothelial cells, red and white blood cells)
muscle ( smooth, skeletal, cardiac)
gonads, kidneys, adrenal cortex
What is the notochord
where does it form
what does it do
what is the neural plate
rod like tube structure formed from cartilage like cells
formed along the embryo midline, under the ectoderm
acts as the organizing centre for the neurulation and mesoderm development
describe the process of forming the neural tube
notochord releases growth factors and signalling molecules which organises the embryo to form the neural system
it directs the neural plate ectoderm to invaginate and form a groove
creates two ridges called the neural folds that runs along the cranial caudal axis
neural crest cells develop in the neural folds
neural folds move towards each other over the neural groove, forming a hollow tube (the neural tube) when the folds fuse
the neural tube is overlaid with epidermis
the neural crest cells in the neural folds increase in number and migrate to other areas of embryo
What days do the head end and the tail end of the neural tube close?
what condition arises due to failure of the closure of the tail end of the neural tube
what condition arises due to failure of closure of the head end of the neural tube
the closure of the head end precedes what developing?
day 23 and 27
spina bifida - when the neural tube is open at birth, usually the lower spine, varying severity (0.4-5-1000 births)
anencephaly- absence of most of the skull and brain (1/10,000 births)
formation of brain structures
give examples of the derivatives of the neural crest cells
cranial- cranial nerves
cardiac- aortic arch, cardiac nerves
trunk- dorsal root ganglion, sympathetic ganglion, melanocytes. aortic nerve
clusters, adrenal medulla
vagral and sacral- PNS ganglia, Enteric ganglia
what do defects in neural crest cell migration lead to?
pigmentation disorders
failure to innervate GI tract
deafness
cardiac and facial defects
what is somitogenesis
what are somites
formation of somites
paired blocks of paraxial mesoderm flanking the neural tube and notochord
what is the process of somitogenesis?
what aspects of somite formation is species specific?
blocks of paraxial mesoderm condense and bud off in pairs
one on each side of the neural tube
begins at the cranial end and continues towards the caudal end
appearance of somites
numbers of somite pairs
rate of budding of somite pairs
