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Anatomy 1-5 Early Development
Lecture 9.01 on Early development
33
Anatomy
Professional
09/05/2011

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Term
The 2 cell zygote undergoes cleavage. What is cleavage?
Definition
Division to increase number of cells without an increase in size.
Term
What are early cells in the zygote called?
Definition
blastomeres
Term
How many cells are in the morula stage?
Definition
32
Term
Which embryonic stage undergoes compactation? What does compactation do?
Definition
The morula undergoes compactation which divides them into an inner and outer cell mass.
Term
What happens when the morula enters the uterine cavity?
Definition
The fluid filled blastocyst cavity is formed, the whole complex is called the blastocyst, and the inner cell mass becomes the embryoblast while the outer cell mass becomes the embryoblast
Term
About how long after fertilization does the blastocyst attach to the posterior uterine wall?
Definition
5-6 days
Term
What do the trophoblast cells at the embryonic pole of the blastocyst proliferate to become? What is their function?
Definition
syncytiotrophoblasts, which are able to invade the uterine lining.
Term
Where does the embryo typically implant?
Definition
Superior and lateral uterine walls
Term
What part of the blastocyst eventually becomes the placenta? The embryo?
Definition
trophoblast; embryoblast
Term
What happens with the embryoblast immediately after implantation?
Definition
cells differentiate and organize into 2 layers. cells on the future dorsal side of the embryo (near uterine wall) become epiblast or primary ectoderm while cells on the ventral side become the hypoblast (endoderm). Hypoblast+epiblast=bilaminar germ disc
Term
What is happening at around 8 days post-fertilization?
Definition
embryo penetrates further into uterine wall. High proliferation in syncytiotrophoblast and cytotrophoblast. proteolytic enzymes in cytotrophoblast degrade endometrial tissue.
Term
What happens at 9 days?
Definition
cells of the epiblast split in middle to form amniotic cavity, some hypoblasts converge away from the bilaminar disc to form primary yolk sac
Term
What happens to the primary yolk sac?
Definition
On day 12, a second wave of cells migrates ventrally to form the secondary (definitive) yolk sac, which closes the primary yolk sac. The primary sac moves to the abembryonic pole and eventually disappears
Term
What is the name of the stalk that encloses the definitive yolk sac and bilaminar germ disc?
Definition
connecting stalk (eventually becomes umbilical cord)
Term
At what region of the embryo is the primitive streak located? The buccopharyngeal membrane?
Definition
caudal end of the embryo; cranial end of embryo *cranial extent of gastrointestinal tract
Term
What 3 components make up the primitive streak?
Definition
primitive pit, primitive groove, primitive node
Term
What is the cloacal membrane?
Definition
It defines the caudal extent of the gastrointestinal tract
Term
How are the 3 definitive germ layers formed? On which days does this occur? What is this process called?
Definition
Epiblasts xform into undifferentiated mesenchymal cells that invade hypoblast, replacing it with definitive endoderm. 2nd wave of migrating cells forms a new layer, definitive mesoderm. Remaining epiblasts become definitive ectoderm. Occurs at day 14-16. This is called gastrulation.
Term
What is the embryo called immediately following gastrulation?
Definition
trilaminar germ disc
Term
How do the notochordal process and the heart form?
Definition
mesodermal cells migrate laterally and cranially. cells cranial to the primitive pit that remain in midline become the notochordal process
Term
How does the notochord form?
Definition
notochord develops from notochordal process. It looses its lumen and becomes a solid tube. it also converts ectoderm overlying it into neuroectoderm, forming the neural tube
Term
How does the notochord influence the growth of the neural plate?
Definition
induction of neural plate cells by the notochord cause its growth into neuroectodermal cells.
Term
What are the different parts of the neural plate?
Definition
neural fold, neural groove, and neural crest
Term
What part of the neural plate becomes the neural crest? The neural tube?
Definition
neural crest; neural folds
Term
What do the neural crest cells become?
Definition
dorsal root and autonomic ganglia
Term
What are the last portions of the neural tube to close?
Definition
cranial and caudal neuropores
Term
What are some of the causes of inneffective closure of the neuropores? What results from this?
Definition
gene mutations or teratogenic mechanisms; congenital defects or malformation of spinal cord/brain
Term
What happens to the mesoderm lateral to the neural tube? Why is this patterning significant?
Definition
mesoderm organizes into somites. segmental pattern serves as a template that is important in development of musculo-skeletal and nervous system interrelationships
Term
How does the 3 dimensional embryo form? What body parts are translocated in this process?
Definition
cranial, caudal, lateral folding of the germ disc; septum transversum, cardiogenic region, and distal hindgut
Term
Why does the embryo come together in the midline during the process of lateral folding?
Definition
growth and development of neural tube, heart, gastrointestinal tract, and decrease in size of the yolk sac
Term
What is the septum tranversum? What does it separate? How do these two regions communicate
Definition
developing diaphragm; separates the intraembryonic coelom into thorax and abdomen, called at this stage the pericardial and peritoneal cavities. They communicate through the pleuroperitoneal canals
Term
What eventually closes the pleuroperitoneal canals?
Definition
the pleuroperitoneal membranes grow out bilaterally from the posterior body wall towards the septum transversum and then fuse
Term
What happens when the pleuroperitoneal membrane fails to fuse with the septum transversum or fails to form?
Definition
An opening in diaphragm results where abdominal contents can enter thoracic cavity, called congenital diaphragmatic hernia. stomach and small intestines compromise developing lungs and compress the heart
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