Early Embrology Flashcards
1
Q
define capacitation
A
- removal of seminal proteins from the surface that allows penetration through corona radiata and then through the zona pellucida
2
Q
describe the acrosome reaction
A
- release of acrosomal enzymes (acrosin, etc)
- penetration of sperm through zona pellucida
- this leads to the fusion of the plasma membrane of sperm and ooctyte
- changes in the zona pellucida inactivates sperm receptors and prevents polyspermy
3
Q
describe fertilization and meiosis of oocyte
A
- fertilization stimulates completion of the 2nd meiotic division to form the mature oocyte (nucleus = female pronucleus)
- sperm nucleus forms the male pronucleus
- fusion of pronuclei restores the normal diploid number in the new organism (zygote)
4
Q
describe cleavage in week 1
A
- cleavage: repeated mitotic division of the zygote to produce daughter cells or blastomeres
- the zona pellucida is preserved –> no increase in size of the conceptus
- compaction occurs: cell to cell interaction
- after 12-32 blastomeres, morula forms
5
Q
name the 2 distinct cell populations found in the cleavage phase
A
- 2 distinct cellular population can be identified:
- centrally located cells or inner cell mass (embryoblast) –> embryo
- peripheral cells (trophoblast) –> placenta
- secretes early pregnancy factor
6
Q
describe the blastocyst formation
A
- blastocystic cavity is formed between the trophoblast and inner cell mass
- embryonic pole containing the embryoblast is now seen
- zona pellucida shed around day 5
- blastocyst attaches to endometrium around 6th day
- trophoblast begins to proliferate and implantation begins
7
Q
describe the 2 distinct layers of the trophoblast upon implantation
A
- inner cytotrophoblast
- mitotically active
- contributes cells to the syncytiotrophoblast
- outer syncytiotrophoblast
- mass of cells or syncytium at the embryonic pole
- erode endometrial connective tissue
8
Q
describe implantation and ectopic pregnancy
A
- abnormal sites of implantation may cause ectopic pregnancy
- signs and symptoms:
- missed period
- abdominal pain
- HCG lower than expected
- can cause tubal rupture and hemorrhage
- causes:
- factors that delay or prevent transport
- treatment:
- termination of pregnancy
- possible removal of tube
9
Q
describe the bilaminar disc formation in week 2
A
- inner cell mass (embryoblast) reorganizes into a bilaminar disc with 2 distinct cell types:
-
epiblast (main)
- amniogenic cells from the epiblast line the trophoblast to enclose a cavity –> aminiotic cavity
-
hypoblast
- cells migrate to form exocoelomic membrane and cavity which later becomes primary umbilical vesicle
- replaced later by primitive endoderm
-
epiblast (main)
- loose extraembryonic mesoderm forms between cytotrophoblast and exocoelomic membrane
10
Q
describe the fate of the extraembryonic mesoderm (EEM)
A
- the extraembryonic mesoderm (EEM) rapidly proliferates, simultaneously spaces appear within it which later fuse to form a fluid filled extraembryonic coelomic cavity
- the coelomic cavity (chorionic cavity) splits the EEM into 2 layers:
- extraembryonic splanchnic mesoderm
- surround amnion and umbilical vesicle except at connecting stalk
- extraembryonic somatic mesoderm
- lines trophoblast and covers amnion
- extraembryonic splanchnic mesoderm
11
Q
describe the development of chorionic villi in the 2nd week
A
- the coelomic (chorionic) cavity separates the embryo and umbilical vesicle from the outer wall of the implanted blastocyst which later becomes the chorion
12
Q
describe chorionic villus sampling (biopsy)
A
- a chorionic villus samping can be used to diagnose chromosomal, metabolic and sex linked disorders
13
Q
describe development of the uteroplacental circulation
A
- initially, the bilamniar disc receives nutrients and eliminates waste via diffusion of a mixture of maternal blood and cellular debris from glands found in trophoblastic lacunar spaces
- as the embryo grows, the uteroplacental ciruclation is established
