Fertilisation, Implantation & Extra Embryonic Membrane Formation Flashcards
Fertilisation (AKA conception)
Joining of male and female gametes to form a single cell (zygote)
23 chromosomes from each of the gametes to form a total of 46 chromosomes
Female Body
Egg released from ovary & moves to oviduct
Egg moves to uterus via muscular contractions and cilia (~ 4 days)
Egg must be fertilised within 24 hours of its release, or it will lose it capacity to develop further
Male body
150-300 million sperm are released during ejaculation (~ 400 reach the Fallopian tubes, but only 1 will fertilise the egg)
Many are destroyed by the acidic enviro.
Other sperm enter the wrong oviduct
They move through cervix, uterus, & then oviducts thanks to a combination of their motility, ejaculatory force & uterine/oviduct contractions
What are the two layers of the egg?
Outer layer
Corona Radiata
Jelly-like, layers of follicle cells
These cells nourished the egg when it was in a follicle
Inner layer
Zona Pellucida
Protein & Carbs
What happens when sperm meets the CR?
The sperm releases enzymes from it’s cap (acrosome) to digest a path through the protective layers
Once a sperm enters the egg, the eggs plasma membrane polarises, preventing other sperm from binding with it & entering it
Within 12hrs the nuclear membranes of sperm and egg disappear
This is so sperm & egg chromosomes can join
to create a zygote
Cleavage & Implantation
Fertilised egg is still moving through oviduct & is several days away from entering the uterus
Within 30hrs of fertilisation,, the zygote divides via cleavage until it has 16 cells
Cleavage = cell division with no growth in overall
size - v. quic process w/ little time for growth
What is a Morula?
A zygote with 16 cells. Will reach the uterus within 3-5 days after fertilisation
Begins to fill with fluid that diffuses from uterus
As the fluid-filled space devs., 22 different groups
of cells form
What is the structure called after “Morula”?
A Blastocyst
A hollow structure (“pouch”) from which new
cellular structures can develop
5-7 days after fert. The B attaches to the endo. w/ the ICM closest to the wall
What is one of the group of cells created within the Blastocyst?
Trophylblast
Outer nourishing layer of blastocyst that will develop into the chorion (membrane). The chorion will then develop to
form part of the placenta, which provides nutrients and O2 & removes waste from the developing offspring
Once the B is in position, the Troph. Cells will secrete enzymes that digest some of the tissues an blood vessels
of the endo. so the B can implant
Implantation is complete within 10-14 days and te woman is now considered to be pregnant
What is the other group of cells that are in the blastocyst?
The Inner Cell Mass (ICM, Embryoblast)
The ICM devs into the embryo itself
What happens at implantation?
The Trophylblast secretes Human Chorionic Gonadotropin (hCG) which has the same effects as LH
Maintains the CL
Secretion of estro/proges continues
Secretion of hCG continues for 2 mons and decline by the end of 4mths. (Placenta begins to secrete enough hormones to maintain the endo.)
