Flashcards in Placental Physiology Deck (23)
Does the placenta or fetus use more energy?
Uses half of the oxygen and 2/3 of the glucose
5 cellular mechanisms of placental transfer
How is the blood flow in the placenta regulated?
There is no way to autoregulate because the blood is in the intervillous space
Regulation is based on maternal CO/BP and surface area
Key determinate of fetal oxygenation is...
Maternal uterine blood flow (or CO)
How is glucose transported into the placenta?
What 2 things use active transport to move in or out of the placenta?
Amino acids (against concentration gradient to go into the placenta)
Lactate (product of metabolism that needs to go into the maternal circulation)
2 things that move via endocytosis
Leakage or disruption in the feto-maternal barrier
Occurs in normal pregnancies in a small amount due to microtears at the syncytiotrophoblast barrier
Massive hemorrhage can occur from a significant disruption from abruptio placenta
Hemolytic disease of the fetus and newborn
Mom is Rh negative
Exposed to Rh positive RBCs at some point
Makes antibodies against them (anti-D Abs)
Next pregnancy, these Abs can cross the placenta
If Rh negative baby = no prob
If Rh positive = risk of fetal anemia
If mom is Rh negative and no antibodies are tested, when do you give Rhogam?
Standard indications (miscarriage, ectopic, bleeding in pregnancy, 28 weeks, postpartum if newborn really is Rh positive)
The anti-D antibodies will mop up the baby's cells in the mothers circulation before she can make antibodies to them
Does the placenta have endocrine functions?
Makes more steroid and protein hormones than any other endocrine tissue known
Human chorionic gonadotropin
Glycoprotein similar to LH
Produced almost exclusively by syncytiotrophoblasts
Detectable in the blood 8-9 days post-ovulation (about the time of implantation - good for pregnancy tests!)
Action of hCG
Rescue and maintenance of the corpus luteum and therefore progesterone production
At 6-10 weeks the placenta will take over progesterone production
Role in endometrial preparation and implantation
Maintains uterine quiescence during pregnancy (so it doesn't contract and deliver early)
Smooth muscle relaxation, inhibits uterine prostaglandin production, immunological modulation
Placental progesterone is a pool of substrate for production of fetal adrenal corticosteroids
Estrogen (produced by, precursor, actions)
Produced by: placenta
Precursor: maternal androgens initially, fetal androgens later
Actions: increased uterine blood flow and CO (peripheral vasodilation, regulates blood volume by stimulating RAAS), involved in uterine preparation/contractions for labour, preps breast for lactation, etc
5 functions of the amniotic fluid
Cushions the fetus from trauma
Prevents compression of the umbilical cord
Allows room for the fetus to grow and move (important for limb development, critical for lung development)
First trimester amniotic fluid
Initial amniotic fluid in early pregnancy is isotonic with maternal blood
Likely derived from transudate of maternal and fetal plasma
In the second and third trimester, amniotic fluid is produced by what 3 things?
Fetal urine (mainly - kidneys are immature so bad at concentrating urine)
In the second and third trimester, amniotic fluid is resorbed by what 2 things?
Fetal swallowing (mainly)
Intramembranous flow (between fetal compartments)
Too little amniotic fluid
Complications of oligohydramnios
Umbilical cord compression
Too much amniotic fluid