Placental Physiology

Question 1

Does the placenta or fetus use more energy?

Answer 1

Placenta!

Uses half of the oxygen and 2/3 of the glucose

Question 2

5 cellular mechanisms of placental transfer

Answer 2

Simple diffusion
Facilitated diffusion
Active transport
Endocytosis
Fetomaternal hemorrhage

Question 3

How is the blood flow in the placenta regulated?

Answer 3

There is no way to autoregulate because the blood is in the intervillous space
Regulation is based on maternal CO/BP and surface area

Question 4

Key determinate of fetal oxygenation is…

Answer 4

Maternal uterine blood flow (or CO)

Question 5

How is glucose transported into the placenta?

Answer 5

Facilitated transport

Question 6

What 2 things use active transport to move in or out of the placenta?

Answer 6

Amino acids (against concentration gradient to go into the placenta)
Lactate (product of metabolism that needs to go into the maternal circulation)

Question 7

2 things that move via endocytosis

Answer 7

Viruses

IgG

Question 8

Fetomaternal hemorrhage

Answer 8

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

Question 9

Hemolytic disease of the fetus and newborn

Answer 9

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

Question 10

If mom is Rh negative and no antibodies are tested, when do you give Rhogam?

Answer 10

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

Question 11

Does the placenta have endocrine functions?

Answer 11

Yes!

Makes more steroid and protein hormones than any other endocrine tissue known

Question 12

hCG

Answer 12

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!)

Question 13

Action of hCG

Answer 13

Rescue and maintenance of the corpus luteum and therefore progesterone production
At 6-10 weeks the placenta will take over progesterone production

Question 14

Progesterone action

Answer 14

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

Question 15

Estrogen (produced by, precursor, actions)

Answer 15

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

Question 16

5 functions of the amniotic fluid

Answer 16

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)
Bacteriostatic properties
Temperature homeostasis

Question 17

First trimester amniotic fluid

Answer 17

Initial amniotic fluid in early pregnancy is isotonic with maternal blood
Likely derived from transudate of maternal and fetal plasma
Small volume

Question 18

In the second and third trimester, amniotic fluid is produced by what 3 things?

Answer 18

Fetal urine (mainly - kidneys are immature so bad at concentrating urine)
Fetal lung
Fetal skin

Question 19

In the second and third trimester, amniotic fluid is resorbed by what 2 things?

Answer 19

Fetal swallowing (mainly)
Intramembranous flow (between fetal compartments)

Question 20

Oligohydramnios

Answer 20

Too little amniotic fluid

Question 21

Complications of oligohydramnios

Answer 21

Limb contractures
Facial deformities
Pulmonary hypoplasia
Umbilical cord compression
Prematurity
Death

Question 22

Polyhydramnios

Answer 22

Too much amniotic fluid

Question 23

Complications from polyhydramnios

Answer 23

Premature/preterm rupture of the membranes
Preterm labour
Maternal discomfort
Fetal malpresentation in labour
Umbilical cord prolapse
Antepartum and postpartum hemorrhage