Endocrinology: Placental structure and function Flashcards
What are the 3 stages of implantation
Appoisition: Contact of polar trophoblast and endometrium Endometrium develops pinopodes.
Adhesion: Destructions of the zona pellucida
Penetration: Trophoblast invasion, active transport of metabolic substrates.
Explain the anatomy of the developing placenta.
2 layers: inner cytotrophoblast (cell walls) syncytiotrophblast (no cell wall)
At 9 days: 2 layers, within synscytiotrophoblast lacunae form → later form intervillous space
Day 17: Primary stem villous form - outgrowth of cytotrophoblast, inner core of extraembryonic mesoderm
Day 22: Form primary villi
until how many weeks does the placenta weigh more than the foetus
17weeks
How is blood flow to the placenta increased in pregnancy?
Trophoblast invasion of the spiral arteries of the decidua & outer myometrium,
Name 2 observations seen between placental architecture between healthy placenta and PET placenta
- Placental Villi are less developed, fewer branches and less complex vascular loops
- Change in spiral artery architecture
What feature makes the trophoblast open to potential allogenic immune response by the mother?
No epithelial barrier
Are uterine NK cells the same as plasma NK cells.
No
Reduced cytotoxicity
Diagnostic test of NK cells in peripheral blood give no information about uterine cell function
When does uncontrolled trophoblast invasion occur?
Lack of decidual response → e.g. tubal ectopic or scar tissue within the uterus
Haemorrhage without intervention
What is inadequate invasion of decidua and spinal arteries associated with?
Reduced blood supply to the placental bed & growth restriction, hypoxic fetus
- PET
if fetal cells become in contact with maternal circulation why is there not T- or B- immune response?
Syncytiotrophoblast expresses no MHC antigens
What are the 2 points of contact between the placental trophoblast and maternal immune system
1) Villous syncytiotrophoblast is bathed in maternal blood
2) Extravillous cytotrophoblast interacts with uterine tissue.
Does the Extravillous cytotrophoblast produce MHC
Yes - HLA C,G,E not clear why doesn’t cause immune response
→ Uterine NK cells react but seem to enhance blood supply
What substances can cross the placental barrier?
Low molecule weight molecules: gases, Na, urea and H20
Non polar molecules: unconjugated steroids, fatty acids
What is the double Bohr effect & why is it important in O2 exchange
- Fetal Hb had greater affinity for O2 that maternal Hb
- Placenta has high pH (great affinity for O2) whilst maternal blood becomes more acidic due to CO2 - maternal Hb more likely to release O2
How does maternal relative insulin sensitivety help the developing fetes.
High blood glucose and less taken up by maternal tissue
Placental converts 1/3 to lactate
Explained the change of amino acid materialism in pregnancy
Reduced deamination of amino acids in maternal liver, reduced excretion of urea. More amino acids available for fetes. Contraction of amino acids 5 x higher in trophoblast than maternal blood. Urea generated crosses back into maternal blood
What is the volume of amniotic fluid at
8 weeks
20 weeks
34 weeks
15ml
450ml
750ml
What are the 2 layers of placental membranes?
Chorion (cuboidal epithelium)
Amnion
What is the role of bHCG in early pregnancy.
produced by the syncytiotrophoblast from 6-7 days post fertilisation - bind to corpus lute to stop it breaking down → continue to produce progesterone
What other hormones if bHCG structurally similar too>
LH
a group → FSH, TSH
What time is the peak of bHCG
12 weeks
Although the corpus luteum is present throughout pregnancy, when is it progesterone no longer essential
6 weeks
Where is progesterone produced during pregnancy
Trophoblast
What is the main oestrogen of pregnancy?
Estriol (not 17-estradiol in the ovarian cycle)
