Placenta + Twins B&B

Question 1

decidua basalis vs capsularis vs parietalis

Answer 1

decidua = altered uterine lining during pregnancy

decidua basalis: site of implantation, interacts with trophoblast

decidua capsularis: surrounds fetus

decidua parietalis: opposite wall of uterus

Question 2

what are the 2 membranes that surround the developing embryo/fetus?

Answer 2

1. amnion: inner membrane covering fetus, holds amniotic fluid, protects embryo
2. chorion: surrounds amnion/embryo, derived from trophoblast, supporters fetus and amnion

Question 3

basal plate vs chorionic plate of placenta

Answer 3

basal plate = maternal side, in contact with uterine wall, includes maternal decidua basalis

chorionic plate = fetal side, gives rise to chorionic villi (important for gas/nutrient exchange)

Question 4

what are the 2 cell layers of the trophoblast? contrast their roles

Answer 4

1. syncytiotrophoblast: outer layer that invades endometrium and forms lacunae for maternal blood
2. cytotrophoblast: inner layer that proliferates/migrates into the synctiotrophoblast layer, secretes proteolytic enzymes to aid endometrial invasion

both cell layers contribute cellular projections that form the chorionic villi - contacts maternal blood for nutrient/gas exchange

Question 5

what vessels contribute to placental circulation from the maternal and fetal sides, respectively?

Answer 5

maternal side: endometrial/spiral artery brings blood into villous space, and blood leaves via endometrial vein

fetal side: 2 umbilical arteries deliver deoxygenated blood to the chorionic arteries, then capillaries, and 1 umbilical vein carries oxygenated blood back to the fetus

Question 6

from what is the umbilical cord derived?

Answer 6

derived entirely from fetus, from 2 structures:
1. yolk sac: forms umbilical cord
2. allantois (outpouching of hindgut): forms umbilical blood vessels, fibrous remnant becomes urachus

Question 7

why is it important to count the umbilical arteries after delivery of the placenta?

Answer 7

single umbilical artery is associated with fetal anomalies such as aneuploidy or congenital malformations - not diagnostic, but increases the chance there is something else going on you should look for

Question 8

The urachus is a remnant of the embryological ______ and serves as a connection between the _____ and ______. In adults, the remnant is called ________, and may cause ______ cancer.

Answer 8

The urachus is a remnant of the embryological allantois and serves as a connection between the bladder and umbilical cord. In adults, the remnant is called median umbilical ligament, and may cause adenocarcinoma of the bladder

Question 9

how is the fetus protected from maternal immunity?

Answer 9

fetus contains antigens that are foreign to the mother, but is protected by the placenta

trophoblasts do not express many MHC class I antigens and placental secretions block immune responses

Question 10

for each of the following embryological stages, state whether splitting of the embryo would cause mono- or di- chorion and amnion:
a. morula
b. blastocyst
c. implanted blastocyst
d. formed embryonic disc

Answer 10

a. morula (days 1-3) —> dichorionic/ diamniotic
b. blastocyst (days 4-8) —> monochorionic/ diamniotic
c. implanted blastocyst (days 8-13) —> monochorionic/ monoamniotic
d. formed embryonic disc (days 13-15) —> conjoined twins