L17 - Placenta & Intra-Uterine Growth Restriction, Abnormal Fetal Development Flashcards
zygote to blastomere: what are there steps
what happens at day4-5
day 6-7?
days 16+?
zygote, 2 cell, 4 stage 8, then morula after 72 hours then blastocyte after 4 days
days 4-5
bastocyte is when there is a cavity. blastocyte thins out and becomes trophoblast – start of placenta
rest of cells move up and become INNER CELL MASS - creates EMBRYONIC POLE
blastocyte then reaches uterine lumen, ready for implantation
day 6-7 inner cell mass becomes epiblast and hypoblast.
Epiblast forms embryo
Amniotic cavity develops within epiblast mass
days 16+?
3 layers forms from bilaminar disc - gastrulation
– primitive streak initiate
– epiblast –> ectoderm
– hypoblast –> replaced by epiblast cells, become endoderm
– epiblast –> mesoderm
THEN EMBRYO FOLDS
how does the placenta form
syncytiotrophoblast invades decidua
cytotrophoblast erodes maternal spiral arteies and veins
spaces between (lacunae) fill up with maternal blood
this is followed by mesoderm that develops into fetal vessels
this aids transfer nutrients of O2 across simple cellular barrier
what is the difference between cytotrophoblast cells and synctiotrophoblast cells
CTB undifferentiated they invade maternal blood and destroy epithelium they give rise to STB reduce in no as pregnancy goes on
STB
they are fully differentiated
are in direct contact with maternal blood
they produce placental hormones
how does the placenta act as an endocrine organ
HCG
- human chorionic gonadotrophin
- maintains corpus luteum in pregnancy
- progesterone and oestrogen
HPL
- human placental lactogen
- growth, lactation
- carb and lipods
also more
what is the placental barrier like
what goes across this barrier
maternal blood in the lacunae is in direct contact with syncytiotrophoblasts
there is just a monolayer of STB, CTB and fetal capillary epithelium separating fetal and maternal blood
as pregnancy advances, barrier thins leas to greater surface area for exchange
- -gases (o2 co2)
- -water electrolytes
- -steroid hormones
- -proteins poor - pnly via pinocytosis
- -transfer of maternal
- -antbodies IgG starts at 12 weeks – mainly after 34 weeks SO premature infants LACK protection
Parts of the decidua
decidua capsularis: overlay embryo and chorionic cavity
decidua parietalis: side uterus not occuped by embryo
decidua basalis: between uterine wall and chorionic villae
Vasa praevia
what is it
how is it diagnosed
how is it managed
how is this different to placenta praevia
fetal vessels within umbilical cord pass over internal os. when this dilates in labour the vessels are stretched and exposed – can rupture, massive fetal blood loss and death
with ultrasound using colour dopplers
m - delivery by c section when fetus is 34 readings
PLACENTA PRAEVIA
–massive, painless bleeding, fetal and meternal death
what happens if the trophoblast fails to invade the maternal circulation at 12 and 18 weeks?
poor maternal and fetal mixing of blood,
lack od o2 and nutrients to fetus,
leads to fetal growth restriction
pre-eclampsia (raised BP)
what are the different types of placenta accreta
what is the consequence of this
normal, acceta, increta, percreta
Placenta cannot seperate, stays within uterus. uterus cannot contract down, massive bleeding - hysterectomy is req
PLACENTAL ABRUPTION
what is it like and what can happen as csq
massive bleeding in preg - often concealed.
separation of placenta during pregnancy.
extremely painful
fetal death
maternal death
how can the placenta differ in multiple pregnancies (from what to what)
morula cleavage
dichorionic / diamniotic
blastoyte cleavage
monochorionic / diamniotic
implanted blastocyte
monochorionic / monoamniotic
formed embryonic disc
conjoined twins
what are the two types of growth problems for fetuses
SGA
small for gestational age
– less than 5th centile
– normal variant or growth restricted
IUGR
Intra-uterine growth restriction
–less than 5th centile
– growth restricted: failure to achieve growth potential
Fetal growth restiction
what can happen as a result of this
Fetal growth restriction Deficient placental invasion Reduced placental reserve Fetal need exceeds supply IUGR Hypoxia Fetal vascular redistribution Oliguria Abnormal CTG Fetal death
diagnosis of fetal growth restriction
- looks smaller
- clincial measurement of uterine size: symphysis - fundal height SFH
SFH - weeks +/- cms
also ultrasound scan
symmetrical vs asymmetrical growth restriction?
whar are causes of early fetal growth restriction for BOTH of these
SYMMETRICAL
BPD - biparietal diameter of head and abdominal circumference are all reduced
CAUSES: chromosoma anomaly (T21), viral (rubella, CMV), severe placental insufficiency OR normal small baby
in asymmetrical ONLY abdominal circum is reduced
CAUSES– abdominal circum reflects size of fetal liver.
PLACENTAL INSUFFICIENCY - no xs glycogen being deposited within the liver
