Embryology of decidua, chorion, placenta, umbilical cord

Question 1

What is the placenta based of?

Answer 1

From the blastula that implants (6th day) into the uterine wall with the outer mass –> trophoblasts
- fetal component –> trophoblasts + the embryonic mesoderm (chorionic plate)
- maternal component –> endometrium

Question 2

Differentiation of the trophoblasts

Answer 2

8th day
- cytotrophoblasts; inner non nucleated cells
- syncytiotrophoblasts ; outer multinucleated protoplasmic mass

Question 3

Syncytiotrophoblasts lacunae (9th day)

Answer 3

• fused vacuoles that invade the maternal tissue an erode the sinusoids and they bleed into the lacunae ( 11,12th day)

Question 4

How are the villi formed? 13th day

Answer 4

when the cytotrophoblasts proliferate into the syncytiotrophoblasts –> primary villi

secondary villi is formed when the mesodermal cells penatrate the core of the 1st villi (Hofbauer’cells)

tertiary villi form when the mesodermal core begins to diff into blood cells

1. anchoring villi that extend from the chorionic plate to the decidua basalis
2. branches form the stem villi are - free villi fir increasing the SA

Question 5

structure of the placenta

Answer 5

1. Fetal portion
   - chorionic frondosum
   - chorionic plate +its vessels
   - syncytial knots –> pieces of the syncytiotrophoblasts in the intervillous spaces
2. maternal portion
   - decidual basalis; decidual plate w the cells)
   - decidual septa into the intervellous spaces but does not reach the chorionic plate; composed of maternal tissue core and the syncytial cells epi covering
   - cotyledons –> septa that forms to separate the placenta into diff compartments

full term placenta
–> 15-25 cm in diameter and 3cm thick
–> comes out as the after birth material
fetal; chorion plate, amnion, umbilical cord
maternal; decidua basalis + cotyledon

Question 6

amnion cavity formation

Answer 6

As the inner mass of the blastula diff into the hypo and epiblast –> amnion cavity within the epiblasts lined by amnioblasts

Question 7

exocoelomic membrane

Answer 7

• is formed from flattened cells of the hypoblast at the abembryonic pole
• lines the inner surface of the cytotrophoblasts
• new cells form between the two –> extra-embryonic mesoderm (loose CT) derived from the yolk sac itself
  –> large cavities form and fuse = exocoelomic cavity (primitive yolk sac)

Question 8

Extra-embryonic mesoderm

Answer 8

somatic - outer lining onto the cytotrophoblasts and amniotic sac
splanchnic- inner lining onto the exocoelomic cavity

Question 9

secondary yolk sac

Answer 9

day 13
they hypoblasts produce more cells –> secondary yolk sac lined with endoderm –> lying within primitive yolk sac
- during its formation large portions of the exocoelomic cavity are pinched off = exocoelomic cysts within the chorionic cavity

Question 10

Chorion plate and chorion

Answer 10

the somatic extra-embryonic mesoderm + the trophoblasts
- villi cover the entire chorion, during pregnancy at the embryonic pole villi continue to grow and rise as the chorion frondosum
- at the abembryonic pole villi degenerate –> chorion laeve which is smooth

Question 11

umbilical cord development

Answer 11

amnio-ectodermal junction = primitive umbilical ring
- connecing stalk with umbilical vessels
- yolk stalk (vitelline duct) + its vessels
- canal connects the extraembryonic cavities

1. amniotic cavity enlarges and it envelopes the connective and yolk stalk –> primitive umbilical cord

• distally; yolk sac stalk + umbilical vessels
• proximally; intestinal loop and remnants of the allantois
  *cavity is too small for the loop so it goes into the extraembryonic space in the umbilical cord –> physiological umbilical hernia. By the end of the 3rd month move into the embryo body and the canal is obliterated

The yolk sac is sitting in the chorionic cavity and connects to the umbilical cord via its stalk but at the third month it begins to shrink and is obliterated
- the amnionic cavity continues to enlarge and gets in contact with the chorionic cavity (amniochorionic membrane - forms a hydrostatic wedge helps to dilate during birth)

Question 12

Umbilical cord final stages

Answer 12

umbilical vessels + Wharton’s jelly (mucous CT rich in proteoglycans used to protect the vessels)

Question 13

Amniotic fluid

Answer 13

found in the amniotic cavity –> watery fluid; amniotic cells partially and mainly by the maternal blood
- 30ml at 10 week, 450ml at 20 week , 800-1000ml at 37 weeks
protective fluid; jolts and adherence of embryo to amnion + fetal movements
composed; water, urine (20 weeks), antibodies + nutrients and hormones

Question 14

Decidua

Answer 14

• the functional layer of the endometrium
  decidualization happens in response progesterone and implantaion
  1. decidua basalis (formed by the cell - rich in glycogen granules and lipid droplets) at the embryonic pole covering the chorion frondosum
  2. decidua capsularis - over the abembryonic pole