S6 Placental function and Dysfunction Flashcards
where does the placenta come from ?
begins to develop in 2nd week of development
focus developing membranes i.e the sacs supporting the foetus and the placenta
describe the processes of implantation of the conceptus into the endometrium
week 2 summary
outer cell mass - syncytiotrophoblast + cytotrophoblast
inner cell mass - bilaminar disk (epiblast + hypoblast)
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 - membranes fuse - amniochorionic membrane ( this ruptures during labour)
what does implantation achieve?
establishes the basic unit of exchange
- primary, secondary and tertiary villi
anchor the placenta
establish maternal blood flow within the placenta
implantation is interstitial, the uterine epithelium is breached and the conceptus implants within the stroma
describe the structure of the placenta and its adaptation for the exchange of materials between foetal and maternal blood
becomes thinner as the needs of the foetus increase
one layer of trophoblast seperates maternal blood from foetal capillary blood
what is a chorionic villus ?
the placenta is a specialisation of the chorionic membrane. Chronic frondosum are finger-like projections e.g trophoblast all very good for exchange
what is ectopic pregnancy
ectopic pregnancy : implantation outside uterine body, usually fallopian tube but also peritoneal or ovarian, quickly life threatening , conceptus not viable as no decidual cells outside the endometrium
RIF pain
what is placenta praevia?
implantation in lower uterine segment, risk of haemorrhage, needs c section
what is pre-eclampsia
failure of spiral artery remodelling. widespread endothelial dysfunction. may progress to eclampsia – seizures
what is placental insufficiency
placenta doesnt develop so cant maintain pregnancy
how is the invasive force of the trophoblast controlled
transformation of the endometrium to the decidua in the presence of a conceptus. the decidual reaction balances the invasive force of the trophoblast
what is structure of the chorionic villus
in the first trimester, the metabolic needs of the fetus are low so we have a full cyto and syncyto
in the third trimester, cyto number decreases and barrier is at optimal thinness for metabolic transport
so through pregnancy , the placental barrier becomes thinner
describe the role of the placenta as an endocrine organ supporting pregnancy
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 and mammary gland development
progesterone : maintains the pregnant state
also makes other hormones :
Human chorionic gonadotrophin
Human chorionic somatomammotropin (aka human placental lactogen) increases glucose availability to foetus , promotes breast development
describe the hormonal basis of testing for pregnancy
HCG - produced during first 2 months by SCTB, supports the secretory functions of the corpus luteum, excreted in maternal urine
by W11 levels deplete to 0
describe the capillary system within the placenta
the capillary system develops in core of villous stems, contracts CP and connecting stalk - extraembryonic vascular system
maternal blood – spiral arteries – placenta
describe how the heart receives blood within the placenta
heart receives oxygenated blood from mother via placenta in one umbilical vein, by pass the non-functional lungs, return to placenta via the two umbilical arteries (deoxygenated). Vessels radiate to form chorionic vessels under the amnion
describe the amnion within the placenta
as amniotic cavity progresss to chorionic amnion envelops connecting stalk and yolk sac forming primitive umbilical cord containing remnant of allantois. In M3 the chorionic cavity and yolk sac are obliterated due to growth of amnion. The umbilical vessels are surrounded by Wharton jelly for protection
what are the placental hormones influencing maternal metabolism
progesterone - increased appetite
HCS - increases glucose availability to fetus
describe the movement across placenta
passive diffusion : 02, C02, urea, H20, electrolytes flow linked : need good spiral artery remodelling
facilitated diffusion : glucose
Active transport : amino acids, iron, vitamins, glycine
describe feotal immunity
in the placenta, feotal immunity matures as pregnancy progresses, breast feeding also helps, IgG only, greater conc in foetal plasma than maternal
what is teratogenesis
placenta not a true barrier to some things e.g alcohol (lipid soluble so diffuses, can get foetal alcohol syndrome), thalidomide, smoking (also reduces placental flow and growth)
short critical periods (e.g pre-embryonic sensitivity most vulnerable, foetal least) for some structures but CNS is vulnerable throughout
what is Rhesus blood group incompatibility
haemolytic disease, blood group incompatibility of mother and foetus
prophylaxis - mother can make antibodies against foetal Rh antigens, so give anti - D treatment to neutralise as the antibodies cause haemolysis when bind to foetal RBCS
describe infection of the placenta
can be taken up by pinocytosis and moved across placenta e.g rubella (patent ductus arteriosus, cataracts), varicella zoster
what are the symptoms of pre-eclampsia
hypertensions and proteinuria
describe gestational diabetes
risk factors include age,ethincity, high BMI, smoking
can develop into T2DM. poor control can cause a macrosomic foetus (>4500g), stillbirth, increased congenital defects. Test with oral glucose tolerance test
