What are weeks 1-8 of human pregnancy known as? What happens? What follows embryogenesis?
Embryogenesis/organogenesis, when organ primordia are established; fetal period of continued differentiation and growth
After fertilization, what does the zygote undergo? When will blastocyst begin implantation in uterine wall? Without fertilization, what happens to the oocyte?
Cleavage (e.g. morula is multicellular); By the end of the first week; within 24 hours the oocyte degens
After which cleavage do cells max contact with each other? What is this process called and what does it entail? What are the cells known as at this point? What happens to the embryo about 3 days after fertilization?
3rd; compaction, when the inner and outer cells begin to segregate; blastomeres; division into a 16-cell morula
Given the process of compaction, what do inner cells of morula become? Outer cells? What penetrates the intercellular spaces of ICM, and what is the embyro known as at this point?
Inner cell mass (tissues in embryo proper); trophoblasts (placenta); Fluid, forming a blastocoel; aka a blastocyst
What types of cells are in the ICM?
Pluripotent cells, aka embryonic stem cells, giving rise to any cell type in the body
What is the difference between totipotent and pluripotent?
Pluripotent cells can divide into any cell type in the body, whereas totipotent cells can differentiate into any cell type including extraembryonic tissue
When blastocyst is prepared to implant in the uterine wall, what interacts with what? Around what day does this occur? What does the blastocyst hatch from?
L-selectins on trophoblasts with carbohydrate receptors on uterine epi; approx one week (7th day); the zona pellucida!!
What happens if the embryo implants somewhere besides the A or P wall of the uterus? Where can these occur?
Ectopic pregnancy; fallopian tube, cervix, abdominal, Cesarean scar
On what day does the trophoblast differentiate into two layers? What are these two layers? Which of these layers continues to expand into uterine wall?
Day 8; cytotrophoblast (inner layer of mononucleated cells) and syncytiotrophoblast (outer multinucleated layer with indistinct cell boundaries); syncytiotrophoblast
On what day do ICM cells differentiate? Into what two layers? What do these layers form? What does trophoblast invasion mean?
9; hypoblast and epiblast; flat bilaminar disc; Means uterooplacental circulation (into maternal capillaries)
From the blastocyst, what actually will make up the three germ layers? What gives extraembyronic tissues?
Epiblast; hypoblast and trophoblast
What are the three goals of gastrulation? When are these three layers made? What does gastrulation first start with?
1. Form endodermal organs by bringing in embryo areas 2. Surround embryo with capable cells for ectoderm 3. Place mesodermal cells in between; third week; primitive streak on surface of epiblast
What does the primitive streak become?
Groove with the primitive node surrounding a primitive pit at the cephalic end
What happens after primitive streak formation?
Epiblast cells move toward primitive streak, detach from epiblast, and slip beneath the streak (ie invagination)
What happens after invagination?
Some cells displace hypoblast (endoderm), some come between epiblast and endoderm to make mesoderm; those remaining in epiblast are ectoderm
What does endoderm help form? Mesoderm? Ectoderm?
Lining of gut and other internal organs; Muscle, skeletal system, circulatory system; skin, brain, nervous system, other external tissues
If we move the primitive (Hensen's) node around, what can be established?
New body axis (it's an ORGANIZER of gastrulation)
Define neurulation; when does establishment of body axes occur?
process by which neural plate forms the neural tube; before and during gastrulation
Four steps of neurulation?
1. Form and fold neural plate 2. Neural crest elevated 3. Neural folds converge 4. Close neural tube once neural folds are brought into contact with each other
What will divide ectoderm? What are the three major domains, and what do they give rise to?
Neurulation; internally positioned neural tube (forms brain and spinal cord), externally positioned surface ectoderm (skin/epidermis), NCC's will go to new locations to give rise to many cell types
How many sites are there for neural tube closure? How does fusion proceed? What happens if you can't close posterior neuropore? What if you can't close at the other two sites (ie anterior neuropore)? What happens if you can't close along the entire neural tube?
3; bidirectionally; Spina bifida; anencephaly; craniorachischisis
What can help prevent neural tube defects?
Folic acid (form of folate, the water-soluble B-complex vitamin)
What systems can NCC's have a contribution to?
Neural, skin, teeth, head, fact, heart, endocrine, GI
What do NCC's undergo before migrating to contribute to different tissues?
Epi-to-mesenchymal transition at the dorsal neural tube
What are the four regions that neural crests can give rise to along AP axis?
Cranial/cephalic neural crest; cardiac neural crest (septum of cardiac outflow tract and pulmonary artery and aorta separated); trunk (form DRG and symp ganglila); enteric (vagal and sacral): parasymp ganglia of the gut
What can human cardiac NCC's do specifically?
Migrate to pharyngeal arches 3, 4, and 6 and enter the truncus arteriosis (cardiac outflow tract) to generate the septum