Placenta Function Flashcards
When does the placenta develop?
Second week of development
Of which membrane is the placenta a specialisation of ?
Chorionic membrane
Briefly describe which layers are present during the week of 2s
Outer cell mass :syncytiotrophoblast and cytotrophoblast
Inner cell mass : epiblast and hypoblast
Amniotic cavity and yolk sac
When does implantation begins ?
Day 6
At initial contact between endometrium and trophoblast
What is the connecting stalk made of ?
Extraembryonic mesoderm
What happens to the yolk sac during development ?
Disappears, incorporated in proximal umbilical cord
What happens to the amniotic sac ?
Enlarges and surround all of the foetus , occupies all the chorionic cavity
What happens to the chorionic cavity ?
Is occupied by the amniotic sac
What does implantation achieve ?
- Establishes the unit of exchange :villi
- Anchor the placenta
- Establish maternal blood flow to placenta
How do the villi develop ?
Primary villi : finger like projections of trophoblast
Secondary villi : invasion of mesenchyme into core
Tertiary villi : invasion of mesenchyme by fetal vessels
Does the maternal and foetal circulation mix ?
No never,
Separated by at least one layer of trophoblast
What is a chorionic villus ?
Basic unit of exchange , finger like projection of trophoblast containing fetal vessels
Which defect in placental implantation can occur ?
The wrong place : ectopic , placenta praevia
Incomplete invasion :
Placental insufficiency , pre eclampsia
How is invasion during implantation controlled ?
In presence of the conceptus, the endometrium becomes the decidua and the decidua leader reaction balance the invasive force
What is a cotyledon ?
Bulging villus area , surface covered by decidua basalis from uterine wall
Derived from foetal and mother tissue
What changes occur in the villus through the pregnancy ?
Gets thinner for optimal exchange , only one layer of syncytiotrophoblast and capillary endothelium
Which blood vessels are contained in the umbilical cord ? How is the blood and where does it travel ?
2 umbilical arteries : deoxygenated blood from foetus to placenta
1 umbilical vein : oxygenated blood from placenta to foetus
Describe the foetal circulation from the placenta to the foetal body
Placenta > umbilical vein > ductus venosus bypass liver > right atrium > foramen ovale > left atrium > systemic circulation with mixing with pulmonary trunk blood via ductus arteriosus
Which hormones are produced by the placenta ?
Steroid hormones : progesterone , oestrogen
Peptide hormones :
- human chorionic gonadotrophin
- hC somatomammotrophin (aka human placental lactogen)
- hC thyrotrophin
- hC corticotrophin
When is hCG produced and what is its function ?
First 2 months of pregnancy
Support the secretory function of the corpus luteum (oestrogen , progesterone )
What produces hCG ?
Syncytiotrophoblast
Which substance is used to test for pregnancy ?
Human chorionic gonadotrophin , made by syncytiotrophoblast
When does the placenta takes over from the corpus luteum to produce steroid hormones ?
11th week
What effect has progesterone on maternal metabolism ?
Increase appetite for nutrients for embryo and support lactation
What effect does hCS aka hPL have on maternal metabolism ?
Increase glucose available for foetus by inducing insulin resistance in mother
How does gas exchange occur in the placenta and how is it limited ?
Simple diffusion , flow limited so need an adequate uteroplacental circulation
Which substances are actively transported by transporters expressed by syncytiotrophoblast ?
Amino acids , iron , vitamins
Why is the placenta important for foetal immune system ?
Transfer of passive immunity by transfer of IgG by receptor mediated endocytosis
Which pathophysiology can occur as a result of the placenta it being a true barrier ?
- Teratogens can access foetus , influence development
- unintentional physiological response such as haemolytic disease of the new born due to rhesus
What defects can thalidomide cause ?
Limb defects
Which conditions are the consequences of alcohol ?
Foetal alcoholic syndrome
Alcoholic related neurodevelopment disorder
Which drugs are contraindicated in pregnancy ?
ACEi
Anti epileptic drugs (valproate)
Warfarin
Which stages of development are sensitive to teratogenesis ?
Pre embryonic : lethal effects
Embryonic period : very sensitive, systems specific
Foetal period : less , only growth is affected
