Unit 7 - Embryogenesis Flashcards Preview

Molecular and Cellular Princples of Medicine > Unit 7 - Embryogenesis > Flashcards

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


where do human cardiac neural crest cells migrate?

to pharyngeal arches 3, 4, and 6
-enter truncus arteriosus (cardiac outflow tract) to make septum