embroyonic development :) Flashcards
what does human development start out as
oocyte (single cell)
how long does human development take
38 wks
3 trimesters
what are the 3 trimester stages called
pre-embryonic period
embryonic period
fetal period
what occurs in pre embroyonic period and time
embryonic germ layers formed(make the basic tissues needed to form the organism)
0-2.5 wks
embryonic period and time
2.5-8wks
rudiments of most organims and tissues develop
fetal period and time
8wk to 9mn
rudiments grow and mature
called a foetus
what has to form early on
heart and CVS system to push nutrients around the body
what can embroyonic cells do
divide
death (remove cell by apotosis)
fixed/motile (chemical gradients may cause movements)
shape change(may be needed to form polarised cells)
specilalise
what is cleavage
series of cell divisions that subdivides the cytoplasm
what occurs in pre embryonic development
cleavage
morula formation
blastocyte formation
during cleavage…
size of the blastomere stays the same
no cells increases
what is a morula
ball of 16 cells
what happens to the morula
takes up fluid and hollows out to form a blastocyte
what forms the extra emmbryonic structres
trophoblast
what surrounds the blastocyte after 5/6 days and purpose
zona pallucida
prevent sperm entering early
what is found in the blastocyte
inner cell mass (figure of 8 shape)
form the embyro
what does the pre embryo appear as
bilaminar disk (2 cell layers)
what are the 2 layers of the pre embryo
epiblast (upper layer, columnar cells)
hypoblast (lower layer, cuboidal cells)
what occurs after the pre embryo is formed
gastrulation
what is gastrulation
where the 3rd germ layer is formed
gastrulation process steps
epiblast cells move towards the primitive streak(accross the embryonic disk) and invaginate to displace the hypoblast cells
some epilast cells detach and move betwee the epiblast and hypoblast layer
notochord fomration
what does the primitive streak do
estavlished the cranial/caudal ends and the right/left of embryo
what are the three embryonic layers
ectoderm (outer)
mesoderm (middle)
endoderm (inner)
what are the three embryonic layers in terms of abilty to speclise
mulipotent
what does gastrulation allow
basic framework of embryo formed
all adult systems reconisable at 8wks
what happens after gastrulation
organonesis
1st step within that is neuralation
what happens in neuralation
formation of neural tube grt the CNS
as the CNS develops what else develops
another germ layer (ectomesoderm)
neuralation steps
ectoderm thickens in midline(above the notochord) and grows caudally
a crease develops along the axis of the neural plate by invagination
neural folds move together and fuse to form neurla tube
neural crest ells detatch to form the neural crest
where are neural crest cells and what does the neural crest contibute to
on the crest of the neural groove migrating to the mesoderm
formation of peripheral NS
what do crainial neural cells differentaite into
craniofacil cartialge and bones
what do ectoderm cells form
epidermis
hair
mucus epithelium (ie nose mouth)
what do mesoderm cells form
skeletal/musular components
what do endoderm cells form
mucus epithelium (digestive and respiratory)
what do neuroderm cells form
CNS and peripheral nerves
what does the embryo have at 3.5 wks
cranial and caudal ends
pharyngeal arches
how many pairs of pharyngeal arches are there
6 pairs in neck
5 never forms
456 fuse
separated by cleft (externally)
what are the arches called
1 - mandibular
2 - hyoid
3 - glossopharyngeal
what are arches separated by internally
pouches
what is found in each arch
cartilage artyer mesoderm component cranial nerves skeletal component
what does the Hox gene do
each of muscle derived from the arch is innervated by the nerve that arises from the arch
pharyngeal arch nerves
1 - trigeminal V
2- facial VII
3 - glossopharyngeal IX
4- vagus X
what forms the external ear, iddle ear and auditory tube
first cleft - external
corresponding pouch - middle and tube
where do arch deformities mainly occur
1st arch
deformities of 1st arch symptoms
underdeveloped mandible (class II occlusion) malformed external ears absent/reduced malleus/incus
muscle derivaitves 1st arch
muscles of mastication
- myelohyoid
- anterior belly of digastric and tensor veil palatini
muscle derivatives 2nd arch
stylohyoid
posterior belly of digasttic and stapedius
muscle derivatives 3rd arch
stylopharyngeus
muscle derivatives 4th arch
pharyngeal constricutors
soft palate
LTP
intrinsic muscles of larynx
skeletal derivatives 1st arch
meckels cartilage (until mandible forms)
malleus
incus
skeletal derivatives 2nd arch
stapes
styloud process
skeletal derivatives 3rd
hyoid bone
skeletal derivatives 4th
laryngeal cartilages
epiglottis
