Extraembryonic Tissues And Placenta

Question 1

What are the two trophoblastic derivatives that comprise the fetal-maternal interface?

Answer 1

• placenta

- chorion

Question 2

What are the functions of the amnion?

Answer 2

• buffer against mechanical injury
• accommodates growth
• allows normal movements
• protects fetus from adhesions

Question 3

What is hydramnios?

Answer 3

-too much amniotic fluid which could be due to an esophageal atresia or brain damage

Question 4

What is oligohydramnios?

Answer 4

-deficiency of amniotic fluid possibly due to infant not able to excrete urine back into the amnion -> renal agenesis

Question 5

How many phases are there in the formation of amniotic fluid?

Answer 5

-2

Question 6

What happens during phase I of formation of amniotic fluid?

Answer 6

• first 20 weeks of pregnancy
• free diffusion of electrolytes through fetal ectoderm
• maternal serum
• secretion by amniotic membrane

Question 7

What happens during phase II of the formation of amniotic fluid?

Answer 7

• contributions from fetal urine
• filtration for vessels associated with chorion laeve
• other sources?

Question 8

What some functions of the yolk sac?

Answer 8

• may concentrate: folic acid and vitamins (A, B12, and E)
• site of primordial germ cells
• location of blood islands -> origin of initial blood cells (extraembryonic hematopoiesis

Question 9

Where do the umbilical/allantoic vessels develop?

Answer 9

-mesoderm of the allantois

Question 10

How is the allantois associated with the bladder?

Answer 10

-proximal part of allantois is urachus which becomes the median umbilical ligament

Question 11

What are the stages of placental development?

Answer 11

• previllous embryo
• primary villous stage
• secondary villous stage
• tertiary villous stage

Question 12

What characterizes the previllous stage?

Answer 12

-no villi have been formed on the trophoblast

Question 13

What characterizes the primary villous stage?

Answer 13

-solid, cytotrophoblastic, ectodermal primary villi appear

Question 14

What characterizes the secondary villous stage?

Answer 14

-mesodermal cores appear within the primary villi

Question 15

What characterizes the tertiary villous stage?

Answer 15

-characterized by the appearance of blood vessels within the mesenchymal core of the secondary villi

Question 16

What is formed during the final development of the placenta?

Answer 16

• cytotrophoblastic columns
• cytotrophoblastic shells: formed by expansion of columns over the maternal decidua L cells
• anchoring villi: villi anchored to the shell as opposed to floating villi

Question 17

What are the four extraembryonic layers and what are their germ layer derivatives?

Answer 17

• amnion (ICM -> epiblast)
• yolk sac (ICM -> hypoblast)
• chorion (part of fetal maternal interface)
• allantois (ICM -> interfaces with placenta via umbilical cord)

Question 18

Describe the blood flow from the maternal side.

Answer 18

• maternal blood enters intervillous spaces (trophoblastic lacunae) from spiral arteries
• exchange of materials between maternal blood in lacunae and fetal blood in capillaries in the villi
• maternal blood returns to maternal veins in the decidua basalis

Question 19

Describe the fetal blood flow.

Answer 19

• fetal blood is enclosed within vessels
• fetal blood travels to capillary beds within placental villi via umbilical arteries (2)
• fetal blood returns from capillary EDs within placental villi via umbilical vein (1)