Flashcards in Unit 7 - Embryogenesis Deck (27):
what is "embryogenesis"?
weeks 1-8 of human pregnancy
-also "organogenesis" as organ primordia (earliest recognizable stage of development) are established
what is compaction?
after the third cleavage of blastomeres
-max contact with each other, and form compact ball of cells, which form 16-cell morula
what is the inner cell mass?
inner cells of morula
-give rise to tissues in embryo proper
what is the blastocoel?
fluid penegrates into intercellular spaces of ICM to create a blastocyst
when is it considered a blastocyst?
after the blastocoel is formed (outer cells flatten and form wall of blastocyst)
how do trophoblasts attach to uterine wall epithelium?
trophoblast cells penetrate between epithelial cells of uterine mucosa (endometrium)
-L-selectins (CHO-binding PRO) on trophoblast cells interact with CHO receptors on uterine epithelium to mediate attachment of blastocyst to uterus
what does the trophoblast do after implantation?
day 8; differentiates into 2 layers
1. cytotrophoblast - inner layer of mononucleated cells
2. syncytiotrophoblast - outer multinucleated layer that lacks distinct cell boundaries
-continues to expand into uterine wall
on day 9, trophoblast invades maternal capillaries to establish uteroplacental circulation
what does the ICM do after implantation?
day 9; differentiates into flat bilaminar germ disc with 2 layers
1. hypoblast - continue to extraembryonic tissues
2. epiblast - gives rise to all tissues in embryo proper
-amniotic cavity forms within
what are considered extraembryonic tissues?
trophoblast: cytotrophoblast --> syncytiotrophoblast
hypoblast: extraembryonic endoderm --> yolk sac
amniotic ectoderm (from epiblast, but mostly emryonic tissues)
what are the goals of gastrulation?
1. bring inside the embryo areas destined to form endodermal organs
2. surround embryo with cells capable of forming ectoderm
3. place mesodermal cells in proper positions in between
how does gastrulation begin?
formation of primitive streak on surface of epiblast
-primitive streak becomes narrow groove with primitive node surrounding a primitive pit at the cephalic end
what is invagination? what does this cause?
the "second step" of gastrulation
-epiblast cells migrate toward primitive streak, then detach from epiblast and move through streak to slip beneath it
-some cells displace hypoblast to create endoderm
-other cells between epiblast and new endoderm become mesoderm
-cells remaining in epiblast become ectoderm
what is the source of all germ layers that give rise to all tissues of the embryo?
the epiblast, through gastrulation
what is neurulation? the steps?
process of forming a neural tube
1. formation and folding of neural plate
2. elevation of neural crest
3. convergence of neural folds
4. closure of neural tube when neural folds are brought in contact with one another
what are the major domains of ectoderm after neurulation?
1. internally positioned neural tube (forms brain and spinal cord)
2. externally positioned surface ectoderm that primarily forms epidermis
3. neural crest cells that migrate to new locations to give rise to many cell types
how many sites of closure are there on the neural tube? what happens before complete closure?
-neural folds proceed bidirectionally
-until fusion is complete, cephalic and caudal ends communicate with amniotic cavity via anterior and posterior neuropores
spina bifida VS anacephalopathy VS craniorachischisis
SB: failure to close posterior neuropore (severity varies)
A: failure to close two other sites causes open anterior neuropore (forebrain remains in contact with amniotic fluid and degenerates)
C: complete failure of closure along entire neural tube
what is neural tube closure dependent on?
interplay between genes, environment, and maternal nutrition
how much folic acid can make a difference?
50-70% of NTD can be prevented if women take 400 micrograms of folic acid daily, starting 3 mo prior to conception and continuing through pregnancy
what kind of ectoderm undergoes epithelial to mesenchymal transition?
neural crest cells
-happens at dorsal neural tube, then migrates to give rise to tissues
what is mesenchyme?
loosely organized connective tissue of any origin
what are the 4 types of regions the neural crest cells migrate to?
4 main but overlapping anatomical regions
1. cranial (cephalic) neural crest
2. cardiac neural crest
3. trunk neural crest
4. enteric (vacal and sacral) neural crest
cranial/cephalic neural crest
produces craniofacial cartilage, bone, neurons, glia, and connective tissue
-cells enter pharyngeal arches to give rise to thymic cells, teeth, and bones of middle ear and jaw
cardiac neural crest
subregion of cranial neural crest that develops into melanocytes, neurons, cartilage, and connective tissue
-also makes muscular connective tissue wall and septum of cardiac outflow tract that gives rise to large arteries (aorta and pulmonary artery)
trunk neural crest
migrates to form dorsal root ganglia containing sensory neurons or sympathetic ganglia and adrenal medulla
enteric (vagal and sacral) neural crest
form parasympathetic ganglia of gut