6M: Bilaminar Germ Disc Flashcards
Fertilization
- oocyte (plus corona radiata cells) is ovulated from the ovary and swept into the uterine tube
- spermatozoa (sperm) must undergo:
- capacitation
- acrosome reaction
- sperm can be viable in female reproductive tract for several days
- fertilization occurs 12-24 hours following ovulation (likely occuring in the ampulla)
define:
a. capacitation
b. acrosome reaction
a. biochemical changes to sperm in the uterine tube (removal of glycoprotein coat and seminal plasma proteins & exposure of receptors on sperm acrosome cap)
- allows sperm to penetrate corona cells
b. leads to the penetration of the Zona Pellucida
- sperm bind to the ZP through ZP3 (ligand for receptor on sperm). That binding induces enzyme release from sperm acrosomal cap.
define:
a. cortical reaction
b. zona reaction
a. contact leads to release of lysosomal enzyme from the cortical granules in the oocyte plasma membrane
b. ZP properties are altered to prevent polyspermy
Development of zygote (up to 16 cell stage)
2 cell stage: 30 hpf
4 cell stage: 40 hpf
16 cell stage: 3 days pf (morula)
- ZP persists until early blastocyst stage (about 5 days pf)
- at 8-cell stage, compaction occurs (segregation of inner and outer cells). loss of totipotency
Formation at 3 days
- morula is formed by 3 days with inner and outer cell masses
inner: embryo proper, amnion, yolk sac
outer: trophoblast - enters uterine cavity at about 4 days
Formation at 4.5-6 days
day 4.5-5: fluid penetration into intercellular spaces of the inner cell mass results in blastocoele cavity (creating the blastocyst)
day 5: blastocyst “hatches” from the ZP. Can’t insert into endometrium without hatching.
day 6: Implantation occurs by cell-cell and cell-ECM interactions
Formation at day 7.5
both trophoblast and embryoblast differentiate into 2 layers
Embryoblast: 1. epiblast (with amnioblasts) 2. hypoblast
Trophoblast: 1. syncytiotrophblast: outer multinucleated cell layer. produces hCG which maintains CL 2. cytotrophoblast: inner mononucleated layer that divides and migrates into syncytiotrophoblast and fuse
Formation at day 9
Deeper Embedment
- lacunae formation
- exocoelomic cavity formation (primitive yolk sac)
Formation at day 12
- Syncytiotrophoblast erode maternal capillaries
- trophoblast lacunae connect to maternal sinusoids
- blastocyst starts to protrude into uterus lumen
- extraembryonic/chorionic cavity forms
- exocoelomic membrane splits to become extraembryonic splanchnopleuric membrane and somatopleuric membrane
Formation at day 13
- secondary yolk sac forms
- exocoelomic cysts pinch off
- primary villi form (initial stages of uteroplacental circulation)
- this can lead to a little bit of bleeding
- cytotrophoblast cells surrounded by
syncytiotrophoblast
- connecting stalk forms (later to become the umbilical cord)