The Third Week (Exam 1) Flashcards
What is the appearance of the embryonic disc at the end of the second week
becomes elongated and is broader at the cephalic end
What is gastrulation
formation of the three embryonic layers, forms trilaminar embryonic disc
What does gastrulation establish
the ectoderm, mesoderm, and endoderm germ layers
When will the primitive streak be formed
day 15
How is the primitive streak formed
hypoblast cells induce the epiblast cells to proliferate and migrate towards the midline to form a groove
Where does the primitive groove appear
along the dorsal midline of the epiblast
What occurs to the primitive groove
it deepens
After the primitive groove deepens, it forms what
the primitive streak
What does the primitive streak have
Primitive pit at the cranial end
When does gastrulation occur
Day 16
start using GAS pedal at age 16
How will the epiblast form the three germ cell layers during gastrulation
ingressing epiblast cells first displace the hypoblast cells to form the endoderm
some cells of epiblast occupy the space between teh endoderm and the epiblast to form the intraembryonic mesoderm
epiblast cells that do not migrate through are now the ectoderm
What will line the yolk sac after gastrulation
endoderm
When is the embryo referred to as trilaminar germ disc
After completion of gastrulation
What is the trilaminar germ disc composed of
ectoderm
intraembryonic mesoderm
endoderm
How is the notochord formed
notochordal process extends from the primitive pit to the prechordal plate
floor of the notochordal process fuses with underlying endoderm and forms a flattened notochordal plate
plate detaches and forms the solid definitive notochord
What is the prechordal plate
an area where epiblast and hypoblast are still contact rostrally–toward the head
The notochord is composed of what types of cells
endoderm and mesoderm
What will form from the prechordal plate
head stuff
What will form from the cloacal plate
gut stuff
What are the functions of the notochord
directs CNS development
development of the vertebral column (through induction of ectoderm)
determins anatomic midline
forms the nucleus pulposis of IV disc
What remnant of the notochord is seen in adults
nucleus pulposis of IV disc
What is a neurenteric canal
opening between the amnion and yolk sac at the primitive pit
What is the clinical significance of the neurenteric canal
neurenteric cysts may form
What are neurenteric cysts
masses of endodermally derived tissue commonly associated with the spinal cord
How are the ends of the gut tube formed
two depressions arise in the ectoderm, one at cranial end and one at caudal end and form ends of gut tube
What is the depression at the caudal end
cloacal membrane
What is the depression at the cranial end
buccopharyngeal membrane
What is a longitudinal fold
head to tail folding of the embryo
What plane does the longitudinal fold occur in
midsagittal plane
What cuases the longitudinal fold to occur
rapid growth of the brain, but slower rate of growth of trunk and limbs
What are the major results of the longitudinal fold
reposition of the cardiogenic area, portion of yolk sac becomes incorporated into the embryo to form the gut tube
When does longitudinal folding occur
end of 3rd week
What is transverse embryonic folding
two lateral edges of ectoderm fuse with each other ventrally
What causes transverse embryonic folding
rapid growth of the somites, CNS, and differential cell growth
What will embryonic folding results in
tubular embryo (no longer a flat trilaminar embryo)
When will the primitive streak regress
after week 4
What is holoprosencephaly
abnormal face defects, enlarged brain, deficiency of midline head structures
What is holoprosencephaly a result of
innapropriate death of midline cells
What causes Ectopia cordis
lateral foldings not complete, did not enclose thoracic organs
WHat is ectopia cordis
heart outside chest
What are the primitive streak and primitive node essential in
determining body axes
What is situs inversus
organs are on opposite side of the body
What is complete situs inversus
all organs are mirror image of normal orientation
What is incomplete situs inversus
only a single organ is involved
What is sirenomelia
lower limbs fused together, caudal dysgenesis
What causes sirenomelia
inadequate mesoderm in caudal regions
What causes a sacrococcygeal teratoma
persistence of primitive streak and pluripotent cells
What is a teratoma
all germ layers present (ectoderm, mesoderm, and endoderm)
The third week is known as the week of 3’s, what things form
3 layers
3 cavities
3 layers in the villi
At the beginning of the third week, what is the embryo composed of
hypoblast and epiblast
