Human Gastrulation Flashcards
How large is a human yolk?
Human eggs have very little yolk.
What is a blastocyst?
A blastocyst is the human equivalent of the blastula.
What happens at the end of cleavage for humans? (2)
o At the end of cleavage, the embryo consist of the inner cell mass which is a cluster of cells at one end of the blastocyst.
o The trophoblast is the outer layer of the blastocyst and does not form part of the embryo.
When does the trophoblast initiate implantation?
Instead, the trophoblast initiates implantation once the blastocyst reach the uterus on day 7.
What takes place during implantation in humans? (3)
o During implantation, the trophoblast secretes enzymes that break the uterine lining allowing the
blastocyst to be implanted.
o The cells of the inner cell mass form a flat disc.
o The inner layer of the cell mass is the epiblast and the outer layer is the hypoblast.
What does the trophoblast form upon implantation?
The trophoblast also forms finger-like projections and structures called Chorion.
What happens to the epiblast following implantation? (3)
o Following implantation the cells of the epiblast migrate to form a primitive streak.
o Some of those cells will give rise to the endoderm, mesoderm, and ectoderm.
o Four extraembryonic membranes form from the epiblast
What happens at the end of end of gastrulation on humans? (2)
o At the end of gastrulation, four distinct membranes surround the embryo.
o The cells of the trophoblast, epiblast and the endometrial tissues will form the placenta.
Process of gastrulation in humans. (4)
- Blastocyst reaches the uterus
- Blastocyst implants (7 days after fertilisation)
- Extraembryonic membranes start to form (10-11 days) and gastrulation begins (13 days).
- Gastrulation has produced a three-layered embryo with four extraembryonic membranes: the amnion, chorion, yolk sac, and allantois.
Just like in chicks, gastrulation in humans forms a ____ _____.
primitive streak
When does the placenta form?
In two weeks the extra-embryonic membranes develop into the placenta.
What are amniotes?
o Embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell or the uterus.
o Organisms with these adaptations are called amniotes.
What do amniotes form? (3)
o These organisms form four extra embryonic membranes (Chorion, Allantois, Amnion, and Yolk sac)
o These provide a life-support system for the further development of the embryo.
o This is an adaptation to reproducing outside of aqueous environments.
The four extra embryonic membranes that form around the embryo are:
Chorion, amnion, yolk sac & allantois.
What is the function of the chorion?
Functions in gas exchange
