Embryonic Development Flashcards
What events occur in the formation of the blastocyst?
Define blastocyst
Fertilisation forms zygote, cleavage of zygote to form blastomeres, which are totipotent cells (cleavage is an example of where there is no cell growth, simply hyperplasia)
At the 32 cell stage, some cells aggregate in the centre, known as inner cell mass, and others aggregate on the outside, known as trophoblast.
This blastocyst begins absorbing fluid, into a cavity created by the trophoblast known as the blastocyst cavity
On roughly what day does implantation occur? What has to occur for the blastocyst to implant in the uterine lining?
Day 5
Blastocyst must hatch from the zona pellucida and the trophoblast must adhere to the endometrium
What occurs when implantation takes place?
Decidual reaction - endometrial stroma differentiate into secretory decidual cells and the local endometrium becomes highly vascularised and oedematous
Trophoblast cells proliferate and invade the endometrium drawing blastocyst into the uterine wall
On what day does the embryoblast begin to form new layers, what is this layered structure called, and what are the two layers?
Day 14, embryoblast splits to form bilaminar disc.
The two layers are the epiblast and the hypoblast
What cavity develops after the bilaminar disc forms, and where?
Amniotic cavity, between the epiblast and the trophoblast
What happens to the amniotic cavity, and what does it eventually form?
The epiblast cells encircle the amniotic cavity, and form the amnion
What do the hypoblast cells do whilst the amnion is being formed?
They migrate in to form the primary yolk sac, initially, and this then becomes the secondary yolk sac
What are the names of the two cell populations that migrate from the hypoblast?
Extra-embryonic endoderm and extra-embryonic mesoderm
Which of the two migrating hypoblast populations splits, and what does it split to form?
Extra-embryonic mesoderm - forms chorionic cavity
What does gastrulation begin with, and what happens during it?
When bilaminar embryo becomes three-layered, initiated by the formation of the primitive streak
What is formed by ectoderm?
Skin and CNS
What is formed by mesoderm?
Skeletal, connective, muscle and blood tissues
What is formed by endoderm?
Gut tube and associated structures
What do neural crest cells go on to form?
Mesodermal and neural derivatives
