Lecture 24: Embryonic development and placentation

Question 1

What is the inner cell mass (ICM)?

Answer 1

-Will become the fetus
-Trophoblast or trophectoderm- will become part of fetal membranes (chorion) that will elongate. physically contact
-After hatching, chorion rapidly grows laterally (as a “sheet” of cells, 1 cell thick) to occupy space within the uterus
-Other placental membranes grow within the chorion

Question 2

What happens as ICM has contacted the uterus wall?

Answer 2

-Recognition= apportion
-Physical contact= adhesion
-Formation of a functional placenta =invasion
-Series of events
-Genetic compatibility
-Molecular and cellular aspects
-Failure of attachment is the main source of failed pregnancy

Question 3

What happens in placentation in domestic mammals?

Answer 3

Conceptus must
-Move to proper location in the uterus (in cow close to the bifurcation of the IPSILATERAL uterine horn)
-Stimulate production of histotrophy by endometrium (prior to attachment, embryonic synthesis of protein factors, serious)
-Prevent luteolysis (requires P4 dominated uterus: maintain it non-contractile)
-Inhibit maternal immune system (50% of embryonic genomes is “foreign”)
-Establish a placenta (more definitive attachment, more effective transfer nutrient/wastes between mothers and fetus)

Question 4

What are some strategies for retaining luteal function during early gestation?

Answer 4

Rodents: “Luteotropin” release by mating
Primate: chorionic gonadotropin (similar to LH, supports CL)
-Cows, sheep, sows, mares: antiluteolytic mechanism (prevents luteolysis)

All result in maternal recognition of pregnancy

Question 5

What is the importance of conceptus elongation in recognition of bovine pregnancy?

Answer 5

Uterine epithelial cells in the uterine Horn ipsilateral to the CL bearing ovary most important in the luteolytic process:
-Oxytocin binds to oxytocin receptor (uterus)
-PGF2a increases in uterine vein
-Counter-current transfer of PGF2a to ovarian artery
-Luteolysis is initiated