Fertilisation to Trilaminar Flashcards
fertilisation:
union of gametes - fusion of sperm and oocyte to form a zygote
where does fertilisation take place
in the ampulla of the uterine tube
in the firsts stage of fertilisation the Sperm binds to the
zona pellucida glycoprotein (ZP3)
Acrosomal enzymes released from sperm head;
sperm digests its way into egg
Egg and sperm plasma membranes fuse and
sperm contents enters the egg
Sperm entry triggers completion of meiosis 2 and release of
cortical granules by oocyte (make ZP impenetrable to other sperm)
what does one cell embryo undergo
a series ofcleavage divisions
what’s a mitotic division
dividing into identical cells
what else happens during cleavage and why
Rapid mitotic division without increase in size
because cells are confined within the ZP the embryo will change shape(compaction)
what does cleavage form
morula(16+ cells) blastocyst(200-300 cells)
name one type of cell in a blastocyst and explain
Outer cell mass (trophoblast):contacts with the endometrium of the uterus to facilitate implantation and the formation of the placenta
name another type of cell in a blastocyst and explain
Inner cell mass (embryoblast):responsible for the formation of the embryo itself
how to cells maximise available space
by coming into closer contact with each other
Inner cells form
cell junctions
outer cells form
gap junctions
what signals the formation of theblastocyst
Fluid enters through ZP producing a blurred cell mass
describe implantation
Embryo implants into endometrial lining on posterior or anterior uterine wall
Ectopic pregnancy:
implantation outside the uterus
Placenta previa:
placenta lies low in uterus and partially/completely covers cervix
where does the Stella part of the placenta arise from
the trophoblast
what day is implantation typically on
day 6
what occurs in day 7.5
- Trophoblast divides into cytotrophoblast (individual cells) and syncytioblast (single multinucleated cell which produces hCG)
- Embryobast divides into epiblast (dorsal surface) and hypoblast (ventral surface)
- Amniotic cavity begins to form
what occurs during day 9
- Formation of 2 cavities = amniotic cavity (epiblast) and primitive yolk sac (hypoblast)
- Implantation complete and closure by fibrin coagulum
what 2 cavities are formed (day 9)
amniotic cavity (epiblast) and primitive yolk sac (hypoblast)
