Embryogenesis

Question 0

Carnegie stages

Answer 0

System used to describe maturity of embryos, numbers based on features of embryo

Question 1

Embryogenesis and fetal period

Answer 1

Embryogenesis is week 1-8, early stage of organs established
Fetal period is continued differentiation and growth

Question 2

1st week

Ovulation to implantation

Answer 2

Fertilization of oocyte to diploid zygote
Cleavage divisions increases number of cells without increasing size of zygote
3 days, 16 cell morula (totipotent)
Compaction segregates inner cell mass (tissues in embryo, embryonic stem cells) from trophoblast (outer cell, placenta)
Blastocyst formation when trophoblast secretes fluid into morula to create blastocoel (cavitation)
Blastocyst (pluripotent) hatched from zona pellucida (protective layer) to attach to uterine wall

Question 3

Abnormal blastocyst implantation

Answer 3

L-selectins on trophoblast cells interact with carbohydrate receptors on uterine wall
Ectopic pregnancy if on cervix or outside of uterus

Question 4

Differentiation of trophoblast and ICM (2nd week)

Answer 4

Trophoblast:
Cytotrophoblast (inner layer of mononucleated cells)
Syncytiotrophoblast (outer multinucleated layer that proliferates into uterine tissue)

ICM:
Hypoblast and epiblast (both make bilamimar germ disc)

Question 5

Chorion

Answer 5

Trophoblast tissue and blood vessels that fuses with uterine wall to create the placenta
Chorion villi extend, allow exchange of nutrients, O2 and waste

Question 6

Identical vs fraternal twins

Answer 6

Monozygotic vs dizygotic

Question 7

Gastrulation

3rd week

Answer 7

Transforms bilaminar disc into 3 germ layers
First is formation or primitive streak on surface of epiblast, becomes narrow groove, primitive node (Hensen’s, organizer tissue) surrounding primitive pit
Invagination of cells into endoderm (lining of gut, internal organs), mesoderm (muscle, skeletal, circulatory), ectoderm (skin, brain, nervous)
Establishment of body axes occur before and during Gastrulation (anterior-posterior, left-right)

Question 8

Neurulation

Answer 8

Ectoderm separates into neural tube (brain and spinal cord), ectoderm (skin), neural crest (cells migrate to create many cell types like cranial, cardiac, trunk, enteric)

Question 9

Neural tube closure defects

Answer 9

Folic acid prevents

Spina bifida: failure to close posterior neuropore

Anacephaly: failure to close in anterior (cranial) region results in forebrain remaining in contact with amniotic fluid and degeneration