Embryo development and placentation Flashcards
What is fertilisation?
Union of a haploid oocyte and a haploid spermatozoon to produce a diploid zygote
What marks the end of fertilisation?
The initiation of zygote cell division/ cleavage
What is a morula?
8 cell embryo
What happens when the morula becomes compacted?
Forms two layers, the outer cells differentiate to become early trophoblasts and the inner cells stay as a discrete cluster
What is another name for the inner cells?
Inner cell mass
What is the blastocoel ?
Fluid-filled yolk cavity/ space that forms inside the blastocyst during early embryonic development
What do the trophoblasts give rise to?
The fetal membranes (chorion and amnion)
What do the inner membranes give rise to?
Becomes the inner cell mass which forms the embryo itself and two fetal membranes
What is hatching?
The pressure on the zona pellucida increases, trophoblasts release proteases which weaken the wall
What is the placentae?
region of apposition between uterine lining and fetal membranes where metabolites are exchanged
What are some of the functions of the placenta?
Fetal nourishment, waste removal and production of hormones
What is the diffuse placental type?
Exchange occurs across the whole surface area of the placenta (e.g in pigs)
What is the zonary placental type?
Exchange occurs across bands of the placenta (e.g in carnivores)
What is the discoid placental type?
Exchange occurs across one circular section of the placenta (primates and rodents)
What is the name of each daughter cell of the ‘cleavage’ process?
A blastomere
What is the purpose of the outer blastomeres becoming flattened and forming tight junctions?
It reduces fluid permeability
What do the outer and inner blastomeres look like in a morulla?
Outer look compacted, as they begin to form trophoblasts
The inner cells stay as discrete clusters
What do trophoblasts create in the middle of the blastocyst?
The Blastocoele, which is a fluid filled cavity
What are trophoblasts destined to form?
The chorion and the amnion which are fetal membranes of the conceptus
Why do inner blastomeres form gap junctions and what are they destined to become?
Inner blastomeres form gap junctions to maximise intercellular communication and they are destined to become inner cell mass which then goes on to form the embryo itself
How does the hatching of the blastocyst occur?
Blastocyst pumps fluid into the blastocoele, this causes pressure on the zona pellucida
Zona pellucida breaks down and the blastocoele bursts
What is the difference between embryo development in primates and domestic mammals?
In primates the embryo implants rapidly, and extra-embryonic membranes form later
In mammals the extra-embryonic membranes form during a prolonged pre-attachment period
How does the yolks sac form?
Primitive endoderm migrates down over inner cell region which forms the first membrane ‘the yolk sac;
What is a placentome?
A discreet area of interdigitation between a maternal caruncle and a fetal cotyledon
