Implantation and the Early Embryo Flashcards
In vivo how many days after fertilisation does implantation occur?
9 days
Which cells are the early embryo and which are the early placenta?
Inner cell mass - early embryo
Outer cells - placental membranes
What day does the morula reach the uterus?
Around day 3 and 4
Why does the blastocyst have to hatch out from the endometrium?
So that it comes into direct contact with the endometrial epithelium
What hormone causes the endometrial stroma to accept the blastocyst?
Progesterone
What factors cause the conceptus to travel down the ampulla and into the uterus?
Progesterone
Cilia is the most important factor
Does the conceptus increase in size during the first few days after fertilisation?
No, whilst in the oviduct in this first few days each cell undergoes a series of cleavage divisions but the size of the conceptus remains the same. This is because each individual blastomere is reduced is size progressively.
Do maternal, paternal or embryo derived genes influence the first few days of development. Explain why this is.
Maternal. In the early stages of development there is no mRNA synthesis by the conceptus’s own chromosomes as these are unable to undergo transcription at this point. Therefore, all these early stages are controlled by the products of oogenesis and thus the maternal genome. This total dependance on maternal cytoplasmic inheritence means that any deficiency will result in impaired or failed early development and possible pregnancy loss.
On what day does the human conceptus become transcriptionally active?
4 - 8 cell stage (2-3 days)
What are the two distinct parts of the blastocyst?
- An outer ring of trophoblast cells.
2. Inner cell mass (pluripotent cells)
What do the trophoblast cells give rise to?
The extra embryonic tissue ie the chorion
What are the two functions of the zona pellucida after conception?
- Prevents the blastomeres of the conceptus from falling apart during early cleavage prior to compaction. (If they do become divided at this time then monozygotic twins arise)
- Prevents two genetically distinct conceptuses from sticking together.
In humans, is implantation invasive or non invasive?
Invasive
What cells produce LIF?
The cells of the endometrial glands under the influence of oestrogen
What is LIF thought to do with regard to implantation?
Promotes endometrial receptivity to attachment.
What is the cervical mucus plug and what hormone causes it to be formed?
Oestrogen
The production of mucus from glands at the cervix to from a plug acting in a mechanical and antibacterial manner to protect the early pregnancy.
What 4 things does the inner cell mass give rise to?
- Embryo
- Amnion
- Yolk sac
- Allantois
Describe what happens to the endometrial lining after ovulation in preparation fro implantation?
It turns into a secretory lining in preparation of accepting the embryo. It becomes more vascular and it now known as the decidua
What the decidua go on to form if pregnancy occurs?
The maternal part of the placenta
What is gastrulation?
The reorganising of a two layer embryo into a three layer embryo. Also gives the embryo a specific head to tail and front to back orientation.
What are the three germ layers and what roughly do they develop into?
Ectoderm (Skin cells, neurones, pigment cells)
Endoderm (internal layer: internal lung lining, digestive cells)
Mesoderm (Cardiac and skeletal muscle)
When does gastrulation occur? What is the first sign that this is happening?
Around week 3.
The primitive streak (a linear band of cells formed by the migrating epiblast) appears.
