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BMS 2 Week 3 > Early Development > Flashcards

Flashcards in Early Development Deck (10):

Process of Fertilization

  1. Oocyte stalled in 2nd meiotic division
  2. Sperm has undergone capacitation aka matured
  3. Sperm penetrates zona pellucida and corona radiata of oocyte via acrosome reactions (fertilization occurs in ampulla of uterine tube)
  4. Fusion of sperm causes local Ca2+ concentration increases
  5. Ca2+ tsunami results
  6. Cortical granules are released into zona pelucida
  7. Changes in zona pellucida prevent polyspermia and maintain diploid number in zygote
  8. Sperm extrude content into nucleus
    1. nucleus
    2. Centrosome
    3. Microtubules
  9. Oocyte completes 2nd round of meiotic division
  10. Male and female pronuclei combine to form zygote (diploid, 2n)



-What is it?

-Where does it take place?

-How is does it take place?


1. Capacitation is the biochemical changes that allow sperm to fertilize oocyte. 

2. It takes place in uterus and uterine tube. 

3. Chemicals lining the uterus and uterine tube allow sperm to undergo capacitation


Embryonic Development stage

-Includes Morula and Blastocyst formation

1. 1st mitotic division begins

2. First 4 days

  1. several mitotic divisions are symmetric, synchronous, and occur inside zona pellucida

3. Day 5

  1. blastocyst is formed such that it has inner cell mass called embryoblast and outer cell mass called trophoblast

4. Blastocyst hatches from zona pellucida

  1. Trophoblast differentiates into cytotrophoblast and syncytiotrophoblast 

5. Day 6

  1. syncytiotrophoblast invades uterine lining and implantation causes rise in hCG
  2. Embryoblast of blastocyst differentiates into epiblast and hypoblast.
    1. Amniotic cavity forms above or dorsal to epiblast
    2. Blastocyst cavity becomes yolk sac which is ventral to hypoblast

6. Syncitiotrophoblast forms lacunae

7. Syncitiotrophoblast lacunae fill with maternal blood establishing primitive utero-placental circulation

8. Week 3

  1. Placenta matures

9. Primitive yolk sac divides in tear drop like fashion into secondary yolk sac and cyst

10. Hypoblast and epiblast cells are loosely associated except at buccopharyngeal (cranial) and cloacal (caudal) membranes



1. Begins 4th week when zygotic transcription begins

2. Primitive streak appears at caudal end (cloacal membrane) of the dorsal surface of epiblast.

3. Primitive node appears at cranial end of primitive streak

4. Primitive node has single solitary motile cilia that move fluid from right to left

5. Fluid containing vesicles that contain sonic hedge hog protein release contents on left side resulting in changes in gene expression occurring on left side.

6. Cells of primitive streak will delaminate and migrate into primitive node which is area of active invagination into inner embryo

    i.Cells migrate between epiblast and hypoblast to form


    ii.Hypoblast will be invaded by cells to form endoderm

    iii.Remnants of epiblast form ectoderm 


*Epiblast will not invade bucchopharyngeal or cloacal membranes. 




-Cells of primitive node will delaminate

-They will move towards bucchopharingeal membrane to establish midline notochord at cranial end between ectoderm and endoderm 


Normaly location of Implantatioin

Body of uterus 


Common site for ectopic pregnancy 

Ampulla or uterine tube 


Common site for ectopic pregnancy in peritoneal cavity 

Rectouterine pouch 



Results in citus inversus and deafness 


In adult, what is the one remnant of notochord?

-Nucleus purposes is the one remnant

-It is the outer firbous and gelatinous ring on intervertebral disc