gastrulation Flashcards
gastrulation begins with ?
formation of primitive streak on floor of amniotic cavity in epiblast
- moment of individuation - determines left, right
when does gastrulation start?
day 16 of development
what happens in gastrulation?
bilaminar embryonic disc - epiblast + hypoblast - reorganise to trilaminar disc
invagination
cells of epiblast slip beneath the primitive streak
primitive node
raised area surrounding primitive pit, at cephalic end of streak
cell migration + specification are controlled by ____
fibroblast growth factor 8 - FGF8
FGF8 is synthesised by
streak cells
FGF8 controls cell movement by ____?
regulating E-cadherin - protein that normally binds epiblast cells together
all 3 germ layers come from
ectoderm comes specifically from
epiblast
epiblast cells that don’t delaminate (pass through primitive streak)
primitive streak develops on
caudal side
regression of primitive node
the node moves towards the caudal side, shortening the primitive streak
some nodal cells left behind as it moves
line of cells = notochord
notochord
cartilagenous skeletal rod in embryo - formed from regression of node resulting in nodal cells being oriented in line formation
- underlies neural tube
- is signalling centre for inducing axial skeleton
neural tube formation
- neural plate develops in ecctoderm
- neural folds of neural plate approach each other over neural groove
- neural folds fuse to form the neural tube
- some cells at top form neural crest cells - become peripheral nervous system
- mesoderm blocks - called somites - begin to form on either side of neural tube
- brain begins to form at cranial end
fusion of neural plates begins at
+ finishes when?
- cervical region + extends out towards head and tail
- 21-28 days post fertilisation
neural tube closure is difficult because
the neural plates develop significantly before closing
there are many sites of closure in order to close the tube
but defects arise anyways
closure of neural tube fails cranially
anencephaly
- brain + spinal chord fail to develop
- fatal after birth
closure of neural tube fails caudally
spina bifida
to prevent 70% of spinal tube closure defects
take 400µg folic acid 1 month before conception + 2 months after
closed neural tube defects
occulta defects
- less severe
- failure of vertebrae to close at tail end - common + harmless
- malformations of fat, bone
spina bifida occulta - small gap in spine
open neural tube defects
- bones of spinal cord do not form completely - cord bulges out
- paralysis, loss of function, death
secondary neuralation
- neural ectoderm + some cells from endoderm form the medullary cord
- medullary cord condenses, separates to form a canal - then becomes continuous w/ rostral neural tube
when does secondary neuralation take place?
days 20-40
neural crest cell derivative
- neural crest cells migrate out from border between ectoderm + neural plate + develop into:
- peripheral nerves - post-synaptic neurons, sensory neurons, schwann cells
- melanocytes
- some cranial mesenchyme - bones, cartilage, teeth
adrenal medulla consists of _____?
post-synaptic sympathetic neurons - neural crest cell derivatives
somites
blocks of mesoderm cells around neural tube
placode
a part of the ectoderm from which some neural crest cells are derived
neural tube patterning
- patterned along cranial-caudal axis
- floor of neural tube + notochord produce Shh protein - morphogen - governs pattern tissue development
- HOx code is code of patterning
embryonic folding
embryo changes from flat trilaminar disc to cylinder
lateral folding of mesoderm creates _____
gut tube - slanchic mesoderm
body cavity - somatic mesoderm
endoderm gives rise to
gastrointestinal tract
endoderm moves towards MEDIAN midline + fuses
incorporates dorsal part of yolk sac to create primitivegut
- 3 parts - foregut - midgut - hindgut
cranial to caudal
foregut closed by ____
oropharangeal (or buccopharangeal) membrane - becomes mouth
connection between midgut + yolk sac is ___
vitelline duct
hindgut closed by ____
cloacal membrane - becomes anus
during medial embryonic folding the cardiac region is brought to ___
ventral side of developing gut tube
blood supply to foregut
coeliac artery
blood supply to midgut
superior mesenteric artery
blood supply to hindgut
inferior mesenteric artery
lining epithelium of urinary bladder originates from ______ except _______ which is from _______
endoderm
trigone area
mesoderm
4 steps in bladder development
urogenital tract gives rise to the bladder
allantois = revolutionary remnant originally connected to bladder
becomes ligamentous + turns into urachus - connects apex of bladder to umbilicus
becomes median umbilical ligament
what connects apex of bladder to umbilicus during bladder development?
urachus
what evolutionary remnant is left during bladder development and what happens to it?
allantois - becomes ligamentous + turns into urachus which connects apex of bladder to umbilicus - then becomes median umbilical ligament
what gives rise to median umbilical ligament?
urachus - which develops after allantois becomes ligamentous
what does abnormal persistance of allantois lead to and how is this detected?
urine draining from umbilicus after birth - contrast dye is put in bladder through urethra and it is confirmed radiologiclly that dye is passing into the umbilicus
what collects waste during early embryogenesis?
what else does it do?
allantois
- sac w/ many vessels
- gas exchange
passes waste to placenta later
a complication of the hindgut
hirschsprung’s disease
- ganglion cells arising from neural crest cells fail to reach a distant part of the bowel
- abdominal distention, vomiting, constipation, pain
- detected by failure to pass merconium 24-48hrs after birth
- fixable through surgery
vitelline duct abnormalities are caused by ____?
vestigal remnant of vitelline duct remains attached to small intestine
- usually asymptomatic - 2% of live births
umbilical hernia is caused by?
part of small intestine remaining in umbilical cord
omphalocele is caused by ____?
high or low mortality?
failure of intestinal loops to return to body cavity following herniation
- when folding + fusion doesnt occur in 4th-8th weeks, a weakness in body wall allows bowel to herniate later
- high mortality
gastroschisis caused by ____?
high or low mortality?
- protrusion of body contents through abdominal wall into body cavity
- low mortality - excellent survival rate
trachea + lung buds are derived from _____?
the gut - epithelial lining of respiratory tract is from endoderm
esophegeal atresia + tracheo-esophegel fistula caused by ___?
failure of trachea to separate from esophogus
annular pancreas is caused by _____?
problems in rotation of the duodenum - which usually bring dorsal + ventral pancreases together
liver + pancreas arise from ______ during week ___?
foregut
4
somite formation is ___ to ____ + completed by week ___
cranial to caudal
week 3
somite layers + their derivatives
- dermatome - dermi
- myotome - muscles of body wall + limb
- sclerotome - axial skeleton
limbs arise by ___?
induction
- stimulation of specific pathway in one group of cells - responding tissue - by another group - inducing tissue
limb bud formation process
- somites induce the lateral mesoderm to condense + grow outward
- during 4th week limb bud form on lateral plate mesoderm
what induces lateral plae mesoderm to condense + grow outward?
somites
what forms at top of limb bud?
what does it do?
AER - apical ectoderm ridge
it induces progress zone of mesoderm - which differentiates underlying mesoderm
progress zone
undifferentiated rapidly developing mesenchyme in the mesoderm - develops into cartilage + muscle proximodistally (away from) AER
ectoderm gives rise to
skin
nerves - neurons etc.
lateral plate mesoderm gives rise to
- bones
- tendons-
- blood vessels
- ligaments
somites give rise to
musculature
neural crest gives rise to
melanocytes
schwann cells
lateral plate mesoderm ______ into ________ in week _____
condenses
axial mesenchymal columns - presumptive bones
5
axial mesenchymal colums ______ into ______ in week ____
chondrify into cartilage
week 6-8
ossification centres appear in weeks
7-12
how + in what week do muscles start to form?
somites invade limb buds in week 5 - surround axial mesenchymal columns
intermediate mesoderm gives rise to
urogenital system
- develops from mesodermal ridge within mesoderm
earliest kidney structures are _____ in week ____
pronephroi
4
second kidneys are _____ appear at ______ + consist of _________
mesonephroi
end of week 4
- glomeruli + mesonephric tubules opening to mesonephric duct which opens to cloaca
primordia of permanent kidneys are ______ develop in week ___ + finish developing in week _____
2 structures on these which the kidneys develop from are ____ + ______
metanephroi 4 9 urateric bud metanephrogenic blastema
which facial prominences derive from arch 1?
what structure do they form around?
2 maxillary - upper
2 mandibular - lower
stomodeum - primordial mouth
what is frontonasal prominence derived from?
mesenchyme near the brain
what develops on frontonasal prominence in week 5?
what does this structure become?
what happens to rest of structure?
nasal placodes
in week 6 they develop depressions - nasal pits - which become nostrils
nasal placodes divide into lateral + medial nasal proceses
where is the nasolacrimal groove located?
between maxillary prominence + lateral nasal process
cause of oblique facial clefts
failure of the lateral nasal process + maxillary prominence to fuse - leaving nasolacrimal ducts as open grooves
how does the intermaxillary segment form?
from fusing of 2 medial nasal processes
cause of median cleft lift
failure of medial nasal processes to fuse
formation of upper lip and jaw is from
fusing of intermaxillary segment + maxillary prominnces
cause of cleft lip
intermaxillary segment + maxillary prominenc dont fuse
secondary palate development
The secondary palate is formed from two palatine shelves The palatine shelves are tissue extensions from the maxillary prominences
Palatine shelves ascend to horizontal position above tongue and fuse (week 7
primary palate development
intermaxillary segment
incisive foramen
boundary between primary + secondary palate
