Lecture 11 – Pregnancy I (The Placenta) Flashcards
What changes occur to make the endometrium receptive to recieve an embryo?
The glands increase in number and size. There are changes to the surface epithelium (fibroblast like to polygonal). They store gycogen and lipids. Maintained by high progesterone and oestrogen.
What are the three stages of implantation?
Apposition - blastocyte loosely associates with uterine wall
Attachment - blastocyte firmly adheres
Invasion - Attachment triggers enzyme production to begin to invade the tissue.
What is the syncytiotrophoblast?
A multinucleated mass
What are the three main types of placenta?
Haemochoroidal - the chrion is in direct contract with the maternal blood (humans)
Endotheliochoroidal - the maternal blood vessel comes into direct contact with the chorion (dogs and cats)
Epitheliochoroidal - the maternal epithelium comes into contact with the chorion
What are the stages of placenta development?
Lacunae development, primary, secondary and tertiary villi followed by mature villi formation.
How do lacunae form?
In the syncytiotrophoblast erosion by proteolytic enzymes of the maternal blood vessels occurs so there is formation of sinusoids.
How do primary chorionic villi form and when?
They form in the second week of pregnancy. The cytotrophoblast froms finger like projections into the syncytiotrophoblast.
How do secondary villi form and when?
They form around day 16. The extraembryonic mesoderm begins to invade the core of the primary villus.
How do tertiary villi form and when?
Forms around end of week 3. Blood vessels form in the extraembryonic mesoderm within the secondary villi.
What are terminal villi and what are their function?
They are the ends of the branching villi. Little convuluted knots of vessels where the majority of exchange takes place.
What remodelling of maternal vessels takes place for the placenta to serve its function?
The maternal spiral arteries are increased in diameter to get sufficient blood to the placenta. The spiral arteries supply blood to the intervillous space and the endometrial veins drain it.
What is the extravillous trophoblast outgrowth?
The cytotrophoblast columns form over the tips of the villi and eventually form a cytotrophoblast shell. This forms the normal placental dynamics.
What is the EVT plug and what is its function?
The extravillous trophoblast plug occludes the spiral arteries to protect the fetus from oxidative stress. This breaks down after 14 weeks to fill the intervillous space with blood.
What are the maternal adaptations that occur in order to meet fetal demand?
Cardiac output increases (25% goes to placenta)
Increased maternal blood volume
Increased ventilation rate
What 3-4 cell layers seperate the maternal and fetal blood?
fetal capillary, syncytiotrophoblast, cytotrophoblast and connective tissue
