Implantation Flashcards
What is a zygote?
A fertilised egg.
What is a blastocyst?
An early embryonic structure that signifies the first cell differentiation.
What is the trophoblast?
The first epithelium of the embryo, involved in implantation into the uterine wall.
When does conception occur?
Around week 3 of pregnancy (from LMP).
When does implantation occur?
Around week 4 of pregnancy.
Where does the blastocyst usually implant?
Posterior portion of the fundus or body of the uterus.
What is required for initial implantation?
Degradation of zona pellucida and glycocalyx, and reduction of mucin glycoproteins.
What is the function of leukaemia inhibitory factor?
Promotes attachment of the blastocyst to the endometrium.
What are the two layers of trophoblast cells?
- Syncytial trophoblast (multinucleated, outer layer)
- Cytotrophoblast (unicellular, inner layer)
What are trophoblastic lacunae?
Gaps in syncytial trophoblasts that fill with maternal blood and form intervillous spaces.
What two layers form the bilaminar disc?
Epiblast (ectoderm) and hypoblast (endoderm).
What forms the trilaminar disc?
Addition of mesoderm between epiblast and hypoblast.
What does the trilaminar disc fold to form?
Embryo proper
Yolk sac
Allantois
Amnion
What is placentation?
The process of forming the placenta from fetal (chorion) and maternal (decidua basalis) tissues.
What structure connects the embryo to the placenta?
The umbilical cord.
What are the components of the umbilical cord?
2 umbilical arteries
1 umbilical vein
Wharton’s jelly
When is the mature placenta fully formed?
By the beginning of the 12th week.
How does the placenta aid fetal respiration?
Through diffusion of oxygen and CO₂ between maternal and fetal blood.
What nutrient transport mechanisms exist?
Passive and active transport (e.g., glucose via GLUTs, lipids via lipases).
Can IgG cross the placenta?
Yes – it provides passive immunity to the fetus.
Can IgM cross the placenta?
No – which is why some infections are dangerous during pregnancy.
How does fetal hemoglobin differ from adult hemoglobin?
Fetal Hb has 2α and 2γ chains, with higher O₂ affinity.
What does hCG do?
Maintains the corpus luteum and supports early pregnancy.
What is the role of progesterone?
Prevents uterine contractions, essential for maintaining pregnancy.
What does oestrogen promote?
Breast growth, fat deposition, pelvic ligament relaxation.
What is the function of human placental lactogen?
Alters maternal metabolism to support fetal growth (like prolactin).
