Early Embryogenesis

Question 1

embryogenesis

Answer 1

• weeks 1-8 of human pregnancy
• organ primordia (first recognized) are established
• embryonic period followed by fetal period

Question 2

first week of embryogenesis

Answer 2

• oocyte is fertilized in the ampullary region of the uterine tube
• zygote then undergoes cleavage divisions for form a morula and then a blastocyst
• by the end of the first week, the blastocyst begins implantation into the uterine wall

Question 3

fertilization

Answer 3

• results in diploid zygote
• sperm moved to the uterine tube via muscular contractions of the uterine tube and uterus towards ovary
• 30 min or 6 days
• after fusion, male and female pronuclei replicate their DNA and the maternal and paternal chromosomes organize for mitotic division
• the duplicated chromosome sets (23 of each) split to provide each cell of the two cell zygote normal diploid number of chromosomes
• activates cleavage divisions

Question 4

cleavage divisions

Answer 4

• mitotic divisions
• reduce the size and increase number of cells
• blastomeres is cell type
• after third cleavage, blastomeres maximize their contact with each other and form a compact ball of cells- compaction
• 3 days after fertilization, the compacted embryo divides to form a 16-cell morula

Question 5

compaction

Answer 5

• after 3rd cleavage

- segregates inner cells from outer cells

Question 6

blastocyst formation

Answer 6

• inner cells of the morula constitute the inner cell mass
• ICM gives right to tissues in embryo proper and outer cells give rise to the trophoblast that later contributes to the placenta
• fluid then penetrates into the intercellular spaces of the ICM to form a blastocoel
• embryo now blastocytes
• outer cells flatten and form the wall of the blastocyst

Question 7

ICM

Answer 7

• pluripotent cells that give rise to embryo
• ESCs
• trophoblast cells contribute to extraembryonic tissues

Question 8

embryonic stem cells

Answer 8

• ESCs
• derived from the inner cell mass of the embryo
• pluripotent
• potential to treat a variety of diseases such as diabetes, AD, parkinson’s
• ethical issues since they are harvested from viable embryo
• induced pluripotent cells are alternative and generated from adult

Question 9

trophoblast cells

Answer 9

• attach to uterine wall epithelium
• penetrate between the epithelial cells of the uterine mucosa
• recent studies suggest that molecules called L selectins on trophoblast cells interact with carb receptors in the uterine epithelium to mediate attachment of blastocyst
• on day 8, blastocyst partially embedded in endometrium and differentiates into two layers
• cytotrophoblast
• syncytiotrophoblast

Question 10

cytotrophblast

Answer 10

• inner layer of mononucleated cells

- stay cell like

Question 11

syncytiotrophoblast

Answer 11

• outer multinucleated layer that lacks distinct cells boundaries
• continues to expand into uterine wall

Question 12

bilaminar germ disc

Answer 12

• on day 9, ICM differentiates in hypoblast and epiblast
• form flat bilaminar disc
• amniotic cavity forms within the epiblast
• trophoblast invades maternal capillaries to establish uteroplacental circulation
• epiblast gives rise to embryo proper
• -hypoblast and trophoblast contribute to extraembryonic tissues

Question 13

ectopic pregnancy

Answer 13

• abnormal implantation
• 2% of all pregnancies
• 9% of all pregnancy related maternal deaths
• 95-95% all in tube
• can occur in ovary, cervix, cesarean scar, abdominal

Question 14

goals of gastrulation

Answer 14

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 in between
   - begins with formation of primitive streak on the surface of epiblast
   - becomes a narrow groove with a structure called the primitive node surrounding primitive pit at cephalic end

Question 15

invagination

Answer 15

• epiblast cells migrate into primitive streak
• epiblast cells migrate toward primitive streak and then detach from epiblast and move through the streak to slip beneath it
• once cells have invaginated, they displace the hypoblast to create endoderm
• other cells lie in between epiblast and new endoderm to form mesoderm
• cells remaining are ectoderm

Question 16

ectoderm products

Answer 16

• epidermal layer of skin
• neurons of brain
• NCC- pigment cells

Question 17

mesoderm products

Answer 17

• notochord
• bone tissue
• tubule cell of kidney
• RBCs
• facial muscle

Question 18

endoderm products

Answer 18

• stomach cells
• thyroid cell
• lung cell

Question 19

neurulation

Answer 19

• forming neural tube
  1. formation and folding of neural plate
  2. elevation of neural crest
  3. convergence of the neural folds
  4. closure of the neural tube where neural folds are brought in contact with one another
• NCC migrate away to contribute to several tissues, which leaves neural tube separate from epidermis
• neural tube comes from neuroectoderm

Question 20

division of neural ectoderm

Answer 20

• neurulation divides neural ectoderm into three distinct domains
• surface ecoterms
• NCC
• neural tube

Question 21

surface ectoderm

Answer 21

• epidermis
• hair
• nails
• sebaceous glands
• olfactory epit
• mout epithelium-ant pit, tooth enamel, cheek epi
• lens/cornea

Question 22

NCC

Answer 22

• PeripheralNS–> schwann cells, neuroglial cells, SNS, PNS
• adrenal medullar
• melanocytes
• facial cartilage
• dentine of teeth

Question 23

neural tube

Answer 23

• brain
• neural pituitary
• spinal cord
• motor neurons
• retina

Question 24

neural tube closure

Answer 24

• three sites
• fusion proceeds bidirectionally from each site
• until complete, cephalic and caudal ends of neural tube communicate with amniotic cavity via ant and post neuropores
• failure of closure of posterior neuropore- spina bifida
• failure of other two sites to close- anencephaly- forebrain in contact with amniotic fluid and degenerates
• complete failure of closure along entire neural tube is craniorachischisis
• genes and environment
• Pax3, SHH, folate and cholesterol

Question 25

trends in spina bifida

Answer 25

-50-70% of neural tube defects can be prevented if women take 400 micrograms of folic acid daily beginning 3 months prior to conception and continuing throughout pregnancy

Question 26

NCC 2

Answer 26

- migrate away from neural tube to contribute to several tissues - smooth muscle cells - osteoblasts/clasts - adipocytes - chondrocytes - melanocytes - schwann cells - neurons - undergo epithelial to mesenchymal transition at dorsal neural tube

Question 27

types of NCC

Answer 27

- trunk-DRG with sensory neurons or SNS and adrenal medulla - enteric-PNS of gut - cardiac-melanocytes, neurons, cart, CT. muscular CT wall and septum of cardiac outflow tract that gives rise to large arteries (arches 3,4,6 and enter truncus arteriosus - cephalic- craniofacial cart, bone, neurons, glia, CT. also give rise to thymic cells by entering pharyngeal arches. teeth, bones of middle ear and jaw