S6.1 Placental Function & Dysfunction Flashcards
Describe the structure of the conceptus during week 2 of development
Outer cell mass = syncytiotrophoblast + cytotrophoblast
Inner cell mass = bilaminar disk (epiblast + hypoblast)
Describe the processes of implantation of the conceptus into the endometrium
End of W2 conceptus implanted, amniotic cavity and yolk sac suspended by connecting stalk within the chorionic cavity.
Yolk sac disappears.
Amniotic sac enlarges (growth of embryo + amniotic fluid), chorionic sac becomes occupied by expanding amniotic sac, the membranes fuse forming the amniochorionic membrane (this ruptures during labour)
What does implantation achieve?
Establishes the basic unit of exchange - villi
Anchors the placenta
Establishes maternal blood flow within the placenta
Describe the structure of the placenta and how this maximises exchange between foetal and maternal blood
Placenta becomes thinner as the needs of the foetus increase. One layer of trophoblast separates maternal blood from foetal capillary blood.
What is a chorionic villus?
Unit of exchange of the placenta
Describe an ectopic preganncy
Implantation outside uterine body, usually Fallopian tube.
Life-threatening, conceptus not viable as no decidual cells outside endometrium.
Iliac fossa pain
Describe placenta praevia
Implantation in lower uterine segment
Risk of haemorrhage, needs C section
Describe pre-eclampsia
Failure of spiral artery remodelling.
May progress to eclampsia and then seizures.
Symptoms: hypertension (>150/90) and proteinuria (>0.3g in a day). Can also get papiloedema and clonus
Describe placental insufficiency
Placenta doesn’t develop so can’t maintain pregnancy
How are the forces of implantation controlled?
Transformation of the endometrium to the decidua. The decidual reaction balances the invasive force of the trophoblast.
Describe how the structure of the chorionic villus changes through pregnancy
During the first trimester, the metabolic needs of the foetus aren’t high, so we have a full syncytio and cytotrophoblast.
In third trimester, cyto number decreases, barrier is at optimal thinness for metabolic transport.
So through pregnancy, the placental barrier becomes thinner.
Describe the role of cholesterol synthesised by the placenta
Synthesises cholesterol so oestrogen and progesterone steroids can be formed, taking over from those produced by the corpus luteum by about W11:
Oestriol: stimulates uterine growth
Progesterone: maintains the pregnant state
Describe some other hormones the placenta synthesises
HCG - produced during first 2 months by SCTB, by week 11 levels deplete to 0
Human placental lactogen - increases glucose availability to foetus, promotes breast development
Describe the formation of the primitive umbilical cord
As amniotic cavity fuses with chorionic, the amnion envelops the connecting stalk and yolk sac forming the primitive umbilical cord.
Give examples of how different substances are transported across the placenta
Passive diffusion: O2, CO2
Facilitated diffusion: glucose
Active transport: Amino acids, iron
