Fertilisation to Trilaminar embryo Flashcards
What happens in fertilisation (4 stages)
1) Sperm binds in a human specific interaction with the zona pellucida glycoprotein (ZP3)
2) Acrosomal enzymes released from sperm head; the sperm digests its way into egg.
3) Egg and sperm plasma membrane fuse and sperm contents enter the egg
4) Sperm entry triggers:
- completion of meiosis 2
- release of cortical granules by oocyte
Where does fertilisation occur
Ampulla of uterine tubes
What is cleavage- first cell division
Zygote undergoes series of mitotic divisions which subdivides fertilised egg into many smaller daughter cells called blastomeres
what are blastomeres with up to 8 cells classed as
totipotent- capable of giving rise to any cell type
What is mosaicism
Individuals with 2 or more cell line with different chromosome complements
What is a morula
16+ blastomeres (smaller daughter cells)
What is compaction of morula
Cells confined within zona pellucida
so to maximise space cells come closer in contact with each other begin to form cell junctions
Outer cells in contact with zona pellucida form extensive gap junctions and fluid enters through zona pellucida
What is zona pellucida
the thick transparent membrane surrounding a mammalian ovum before implantation
What is in a blastocyst (when is it formed)
Trophoblast
Zona pellucida
Inner cell mass
Blastocyst cavity
(Morula becomes the blastocyst)
What happens when blastocyst hatches
Embryo interacts directly with endothelial lining of the uterus for implantation,
Zona pellucida was removed before implantation
What day and where does implantation occur
Typically on day 6 on posterior anterior uterine wall
What is corpus luteum
Produces progesterone which is essential in maintaining endometrium for embryo to survive
Stimulated by hCG - hormone for pregnancy tests
on what day does bilaminar embryo (2 germ layers) form
day 7.5 when embryo organises itself into 2 cell layers : Epiblast (dorsal) and Hypoblast (ventral)
What drives active process creating bilaminar embryo
Trophoblast
What is trophoblast
Divided into cytotrophoblast and syncytiotrophoblast
What 2 cavities form on day 9 of bilaminar embryo formation
Amniotic cavity (Epiblast)
Primitive yolk sac (Hypoblast)
What cavity forms on day 12 of bilaminar embryo development
Chorionic cavity
-Formed when extraembryonic mesoderm develops & degenerates
What do some cells do to form definitive (secondary) yolk sac on day 13 of bilaminar embryo development
Hypoblast cells migrate
What is ectopic pregnancy
Implantation outside the uterus which is dangerous and life threatening
What abnormal sites can ectopic pregnancies implant
Ovaries
Uterine tube
Peritoneum (abdominal cavity
Where does the primitive streak appear in week 3
midline at caudal end of epiblast
What is the cranial end of primitive streak
Primitive pit and node
Why is primitive streak involved in gastrulation
Movement of epiblast cells through primitive streak to form 3 germ layers
What do hypoblast cells get replaced by
Definitive endoderm = germ layer
