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83 Cards in this Set

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What does the development of the embryo depend on?
expression of specific genes at a particular temporal and spartial points
What is gene expression regulated by?
hard wired molecular programs and molecules produced by the developing cells or external environment
General name of molecules that guide development?
Transcription factors
How do TFs act?
molecules produced by the genes of the cell that stay within the cell to alter gene function
Define- signaling molecules-
produced by the cell and traffic to other cells to influence those genes
BMP 1-9
Bone morphogenic protein -- signaling molecule

has to be inhibited by the notochord secretion to allow the ectoderm to develop into the CNS
Cadherins
Cell attachment proteins

needs to inhibited to allow the trophoblast to become a connected layer
also inhibited by FGF8 to allow the cells to detach and form 3 layers
FGF 1-10
Fibroblast growth factor 1-10 signaling molecule
Hox a-d
Homeobox containing a-d --transcription factor

does the segmentation of the vertebral column
Lefty
signaling molecule
NCAM
neural cell adhesion molecule- -cellular adhesion molecule

has to be inhibited so the neural crest cells can detach
Nodal
signaling molecule -- important because it activates pip to do the rotation of the heart and its secreion help form the primitive streak
noggin
signaling molecule
Oct-4
Transcription factor - important for early embryonic cleavages
Ptc
Patched --receptor molecule
RA
Retinoic Acid - Retinoid
Shh
Sonic hedgehog - Signaling molecule
TGF- beta1 and beta2
Transforming growth factor -- signaling molecule
At what cell stage is each blastomere able to form a complete organism?
the 8 cell stage
zygote--
formed when the sperm and egg fuse
Does the blastomere cells become larger or smaller with each division?
The cells become smaller and the zona pellucida stays the same size
What does oct-4 do?
regulates early cleavage and maintains the undifferentiated state. Critical for establishing the germ cell and maintaining pluripotency -- with each division the cells have less Oct 4
morula-
at 16 cells formed into a mass and the name changes from blastomere to morula
How is the morula organized?
inner and outer cell mass
What does the inner mass of the morula form?
embryo and contribute components to the fetal membrane (amniotic membrane and chorionic membrane)
What does the outer mass of the morula form?
fetal membranes such as the fetal component of the placenta and umbilical cord
What structurally happens to the outer mass of the morula?

what controls this?
becomes more compact and attach to each other through gap junctions and tight junctions which forms an impermeable boundary

cadherins
What is the zona pellucida?
a glycoprotein that surrounds the ovum, prevents multiple fertilization, immunological barrier between mother and child, prevents blastomeres from dissociating, prevents premature implantation of the embryo until it reaches the uterine wall
What destroys the zona pellucida? when?
destroyed enzymatically by chemicals similar to trypsin secreated from the outer cell mass cells - trophoblast cells by day 5
Why is it important to remove the zona pellucida?
so the embryo can implant in the uterus
What forms the fluid filled blastocyst cavity? when?
At day 6 a fluid forces the inner cell mass away from the outer cell mass everywhere except 1 spot. where the embryoblast stays attached
embryoblast- (where, what does it do)
inner cell mass attached to one side of the blastocyst helps orient the developing embryonic structure
The point with the embryoblast attached to the blastocyst is called what?
the embryonic pole of the blastocyst
What is the first part of the blastocyst to penetrate the uterine wall
the embryonic pole of the blastocyst -- where the embryoblast is attached to the blastocyst
Trophoblast cells -- where, gives rise to
Found as the outer cell mass and lines the blastocyst cavity

Contributes to the placenta
Syncytiotrophoblast--
part of the trophoblast in direct contact with uterine wall.
the cells lose their membrane and become an multinucleated mass that invades the uterus to allow the blastocyst to implant.

Secretes hCG to maintain pregnancy
During day 8 what does the embryoblast differentiate into?
the epiblast (columnar cells in contact with cytotrophoblast) and hypoblast (cubodial cells adjacent to blastocyst cavity)
What forms the amniotic cavity?
the epiblast cells form a cavity
What was the trophoblast before it got that name?
the outer cell mass of the morula
Whats a difference between the two types of trophoblast?
1. the part in contact with the uterine wall is renamed the syncytiotrophoblast and loses its plasma membrane as it becomes a huge cell mass

cytotrophoblast - stays around the blastocyst and keeps its plasma membrane
Which cells form the amnion (amniotic membrane)??
the more dorsal epiblast cells that line the embryonic end of the amniotic cavity
How does the syncytiotrophoblast expand into the uterine lining?
By eroding the endometrium and eroding the maternal blood vessels which becomes the blood supply for the placenta
What changes does the endometrial cells go under during day 8?
They swell with accumulations of glycogen and lipid droplets (this is called decidual reaction and start to secrete interleukin-2 to prevent the cells from attacking the embryo
What prevents the maternal body from attacking the embryo?
the Leukocytes in the endometrium secrete interleukin-2 which prevents recognition
What does the hypoblast give rise to?>
responsible for the formation of many EXTRAembryonic tissues but not the actual embryo
What are the nonmigrating hypoblast cells replaced with?
the cells derived from the epiblast layer - which forms the endoderm
What forms the yolk sac? and name of the cells that line it?
The expanding hypoblast cells from the yolk sac. The cells surrounding it are renamed to exocoelomic membrane
By when does the blood filled lacunae start to appear? what do they form? whats another name?
by day 9-10

start to form the primitive uteroplacental circulation

also known as the primary villus
Gastrulation- when? what does it form? what?
A process of proliferation and migration of epiblast cells through an invagination in the midline of the epiblast. - week 3 -- results in 3 germ layers
What is the primitive streak? when doe it form?
Formed by day 15- its a groove that begins to form at the caudal end of the epiblast layer

It is where the epiblast cells travel through and then form the mesoderm and endoderm
Primitive node-
an expanded mound of cells at the rostral extension
-cells from the primitive node later form the precordal plate and notocord
What 2 signalling molecules induce the formation of the primative streak?
Chordin and nodal
What is secreted from the primitive streak cells? what does it do?
FGF-8 is secreted and inhibits cadherins which allows the epiblast cells to detach and migrate to the primitive streak
What does the primitive streak look like in cross section?
appears as a depression in the midline of the epiblast cell layer
Where does the epiblast cells go after detachment from the epiblast layer?
pass through the primitive streak and some displace the hypoblast cells below to form the endoderm
Which germ layer forms first?
Trick question - -the endoderm and mesoderm form at the same time
How is theintraembryonic mesoderm formed? where is it located?
It is also formed by the epiblast cells (future mesoderm cells) the cells travel through the primitive streak and locate theirself in the middle between the endoderm and epiblast layer
What does the endoderm cells develop into?
linings of the digestive, respiratory, pharyngeal pouches of the head and nech region and urogenital systems
What does the intraembryonic mesoderm develop into?
skeletal, smooth, and cardiac muscle, dermis of skin, portion of kidneys and gonads
What forms the ectoderm cell layer?
the remaining epiblast cells now form the ectoderm
What does the ectoderm form?
nervous system and epidermis of skin
Where are the migrating cells of the primitive streak not allowed to go? why?
Unable to enter 2 midline regions b/c the ectoderm and endoderm are firmly attached to one another to form 2 bilaminar membranes
What are the 2 bilaminar membranes and what do they form?
1. buccopharyngeal membrane- future mouth opening

2. cloacal membrane - future opening for the anus
Where are the 2 bilaminar membranes located?
Buccopharynegeal -area of adhesion between the ectoderm and endoderm at the head end of the embryo

Cloacal membrane - area of adhesion between the ectoderm and endoderm near the caudal end
What happens to the embyo's membrane if you have less that 2 layers? more than 2?
2 layers or less - membrane will rupture

more than 2 - membrane will not rupture
What is one of the first migrations associated with the primitive streak/
the rostral midline migration. -
What does the rostral midline migration form? When does this occur?
forms the prechordal plate and the notochord
by day 18
Where is the prechordal plate located?
the cells that form it migrate toward the buccopharyngeal membrane
Where is the notocord located?
in front of the prechordal plate
What induces the formation of the head and brain?
the prechordal plate
What induces the vetebral column to form? what segments the column?
ssh and Pax (both signaling molecules secreted by the notocord)

segmentation -by hox gene expression
What are the remnants of the notocord?
the nucleus pulposis in the intravetebral disks
What does the notochord secrete? what do these do?
noggin, chordin, ssh, -- these inhibit ectoderm cells from secreting BMP-4 and allows the dorsal ectoderm to develop into the CNS
When does the embryo become unsymmetrical?
when the cells of the primitive node are established their cilia start to beat unidirectionally -- usually left
Define neurulation-
the process that results in the formation of the primitive nervous system
What is neurulation?
process that results in the formation of the primitive nervous system
What forms the neural plate? how? where is it?
the notochord secretes inducing factors which causes the overlying ectoderm to proliferate and thicking forming the neural plate. its location is similar to the primitive streak
What is the process from neural groove to neural tube?
neural groove formed by the neural fold, neural groove deepens by the neural crest, the neural crest encloses and forms the neural tube.
What day does the neural folds fuse to create the neural tube? Where does the fusion begin?
about day 21

6th cervical vertebra and proceeds rostrally and caudally
What are the last portions of the neural tube to close?
the anterior and posterior neuropores
What happens if the anterior neuropore doesnt close?
leads to exposed neural tissue or an exposed brain - usually survive only for a few days - called cranioschisis
What happens if the posterior neuropore doesnt close?
leads to spina bifida -- not fatal
What is the difference between the 2 different types of spina bifida?
1. spina bifida oculta - absence of a portion of the vertebral arch in the lumbosacral region

2. spina bifida cystica- meninges/ spinal cord protrude through the skin
meningomyelocele- both spinal cord and meninges
meningocele - just the meninges