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
What is a maternal caruncle?
The maternal side of the placenta
How does the embryo signal to the mother that it is present?
The embryo prevents luteolysis of the corpus luteum, the corpus luteum releases progesterone which prevents ovulation
What is the main maternal recognition of pregnancy in the pig?
The conceptus secretes oestradiol,
contraction of the uterus muscles which causes pgf2a to be wafted away into the lumen of the uterus where it can’t do anything
What does contraction of the uterus due to oestradiol do in pigs?
Wafts away pgf2a as well as making sure that there is equal distribution of the conceptus’s along the uterine horn
How many conceptuses in each uterine horn of the pig is required for their to be sufficient oestradiol secretion for contraction?
A minimum of two conceptuses in each uterine horn
What is the chorionic girdle and what animal is it found in?
Chorionic girdle is an area of specialised trophoblast cells that form the chorionic girdle- it is found in horses
What is the function of the chorionic girdle?
It forms endometrial cups which secrete ecG and induces ovulation and formation of the secondary corpus luteum
What is the purpose of the chorion?
It is a membrane that surrounds the fetus and helps exchange nutrients, gases etc.
What is the function of prostaglandin f2 alpha?
It releases oxytocin which causes a positive feedback effect leading to the breakdown of the corpus luteum
Which animal produces interferon tau?
Ruminants
What is the function of interferon tau?
It acts on the endometrial cells of the uterus to block oxytocin receptors (so no pathway that breaks down the corpus luteum
What area produces interferon tau?
It is produced by the blastocyst
What is the secondary function of inteferon tau?
Helps promote the attachment of the embryo to the uterus
What initiates luteolysis, what subervts it and why?
Luteolyis is initiated by uterine release of prostaglandin f2 alpha
The embryo subverts this as we need progesterone to signal to the mother that it is there
Where does a cotyledon originate from?
has foetal origin
Where does a caruncle originate from?
Has maternal origin
Where does the chorion and amnion originate from?
trophoblast and mesoderm
Where does the yolk sac originate from?
Endoderm
Where does the allantois originate from?
Mesoderm
What is the name for the new layer of cells formed from the inner cell mass
The new layer of cells that forms the yolk sac (endoderm) is called the hypoblast
The remaining ICM is called the epiblast
What is the allantois an ‘out-pushing’ of?
The primitive gut
What species have an epitheliochorial barrier?
Horses, pigs ruminants
What species have an endothelial barrier?
Carnivores
What species has a hemochorial barrier?
Primates/ Humans
