Embryogenesis (7) Flashcards
When does embryogenesis occur?
Weeks 1-8 of human pregnancy
Generally speaking, what occurs during embryogenesis?
Organ primordia is established
Where is the oocyte fertilized?
In the ampullary region of the uterine tube
What is the order of cleavage divisions?
Zygote 2 cell 4 cell 8 cell Morula Blasocyst
When is the blastocyst formed?
By the end of the 1st week of pregnancy…it begins to implant into the uterine wall
What does fertilization result in?
A diploid zygote
What do cleavage divisions do to the size of the cells and the number of cells?
Decrease size
Increase number
What happens after the third cleavage division?
Blastomeres maximize their contact with each other to form a compact ball of cells (compaction)
What does compaction do to the cells?
Segregates inner cells from outer cells
When is the morula formed?
About 3 days after fertilization?
How many cells are present in the morula?
16 cells
When does each of the following appear after fertilization:
2 cell
4 cell
16 cell
Late morula
2 cell: 30 hours
4 cell: 40 hours
16 cell: 3 days
Late morula: 4 days
What are the components of the blastocyst?
Inner cell mass (ICM) and Outer cells and Blastocoel
What does the ICM give rise to?
Tissues in the embryo proper
What doe the outer cells of the blastocyst give rise to?
The trophoblast that later contributes to the placent
How is the blastocoel formed?
Fluid penetrates the ICM
What type of cells are ICM cells?
Pluripotent stem cells
What do trophoblast cells attach to and how?
Attach to the uterine wall epithelium. They penetrate between the epithelial cells of the uterine mucosa (endometrium)
What are L-selectins?
Carbohydrate binding proteins on the trophoblast cells. They interact with carbohydrate receptors on the uterine epithelium and mediate attachment
What happens in trophoblast differentiation?
2 layers are formed.
Cytotrophoblast: inner layer of mononucleated cells
Synchtiotrophoblast: Outer multinucleated layer that lacks distinct cell bondaries
Which layer of the trophoblast continues to expand into the uterine wall?
Syncytiotrophoblast
What does the ICM differentiate into? When does this occur?
Hypoblast and epiblast. Together these form a flat bilaminar disc.
Occurs at day 9.
What forms within the epiblast?
Amniotic cavity
Where do embryonic tissues arise from?
Epiblast layer if ICM
What does gastrulation achieve?
3 germ layers
What are the goals of gastrulation?
1- Bring inside the embryo areas destined to form endodermal organs
2- Surround the embryo with cells capable of forming ectoderm
3- Place mesodermal cells in proper positions inbetween
When does gastrulation occur? And what does it begin with?
Week 3
Begins with formation of the primitive streak.
What is invagination?
The epiblast cells migrate into the primitive streak after detaching from the epiblast. They move through the streak and slip beneath it
What does invagination give rise to?
Endoderm and mesoderm.
Some cells displace the hypoblast and create endoderm
Some cells lie between epiblast and new endoderm and create mesoderm.
After invagination occurs…what do cells remaining in the epiblast form?
The ectoderm
What does the ectoderm lead to?
Outer surface, CNS, Neural crest
What does the mesoderm lead to?
Muscle, skeletal system, circulatory system
What does the endoderm lead to?
Digestive tube, pharyxn, respiratory tube, other internal organs
What is neurulation?
Process of neural tube formation
What are the steps of neurulation?
1- Formation 2- Folding 3- Elevation of neural crest 4- Convergence 5- Closure
What does neurulation divide the neural ectoderm into?
3 distinct domains:
Neural tube
Neural crest
Surface ectoderm
What do the retina and CNS develop from?
Neural tube
What do the PNS, teeth, melanocytes and facial cartilage develop from?
Neural crest
How many site of neural tube closure is there and how does closure proceed?
3 sites of closure and fusion occurs bidirectionally
What is failure of posterior neural tube closure?
Spina bifida
What is failure of anterior neural tube closure?
Anacephaly
What is complete failure of neural tube closure?
Craniorachischisis
Where does theneural crest cell transition from epithelium to mesenchymal occur?
At the dorsal neural tube (and then after they give rise to tissues)
What are the regions of neural crest cells?
Cranial (cephalic) neural crest
Cardiac neural crest
Trunk neural crest
Enteric (vagal and sacral) neural crest
True or False: Neural crest cells follow distinct migration patterns.
True
