Lecture 25 & 26

Question 1

Describe the formation of the placenta.

Answer 1

.

Question 2

Describe the fetomaternal

junction.

Answer 2

decidua basalis: maternal component

chorion frondosum (villous chorion): fetal component

Question 3

Describe the placental circulation.

Answer 3

• intervillous spaces filled with maternal blood from spiral arteries
• tertiary villi float in the intervillous space
• gas exchange between maternal blood and fetal capillaries

Question 4

Describe how the amniotic fluid is

produced and its circulation.

Answer 4

sources: amnion, maternal blood, fetal urine, skin, and secretions from respiratory tract
circulation: changes every 3 hours

Question 5

Describe the development of allantois

and fetal membranes.

Answer 5

Allantois:

• diverticulum of yolk sac and extends into the body stalk
• obliterates and forms urachus

Amnion:
- forms as fluid filled membranous sac at 2nd week

Chorion:
- primary mesoderm fills space between trophoblastic wall and amnitic cavity adn the primary yolk sac

Question 6

Discuss cleavage of the zygote and

formation of the blastocyst.

Answer 6

fertilization –> blastomere (2 cell) –> 4-cell –> 8 cell –> morula (12-16) –> early blastocyst –> later blastocyst

Question 7

Describe early implantation of the

blastocyst.

Answer 7

• trophoblasts attach to endometrial lining at embryonic pole
• syncytiotrophoblast secrete proteloytic enzymes to erode endometrial lining allowing blastocyst to burrow into endometrial CT

Question 8

Define the term “ectopic pregnancy”

and list the sites of occurrence and the most common site

Answer 8

Anywhere other than endometrium of uterus

most common: ampulla
others: ovaries, abdomen

Question 9

Describe placenta
accreta, percreta
and previa and their clinical significance

Answer 9

placenta accreta: beyond decidua basalis
placenta percreta: through the layers of the uterus
placenta previa: at internal os

Question 10

Describe hydatiform

mole and its association with choriocarcinoma

Answer 10

no or little embryonic tissue present; trophoblast develops, hCG produced, may give rise to choriocarcinoma

Question 11

Describe the cause of hemolytic disease in a newborn(erythroblastosis 
fetalis)

Answer 11

Rh+ baby and Rh- mommy; Ab attack baby

Question 12

Describe embryogenesis of

monozygotic, dizygotic twins and conjoined twins

Answer 12

monozygotic:
- single zygote; identical
- 2 amniotic sacs
- 1 chorionic sac
- 1 placenta

Dizygotic:

• two zygotes
• 2 amnions & 2 chorions
• placentas may fuse

Conjoined:
- incomplete division of embryonic disc

Question 13

Describe the mechanism of

twin to twin transfusion

Answer 13

preferential shunting of arterial blood in one twin to venous blood in the other.

• donor twin: small and anemic
• recipient twin: large and polycythemic

Question 14

Describe the significance of

alpha fetoprotein assay

Answer 14

increased AFP = neural tube defects, anencephaly, and spina bifida

decreased AFP: trisomy 21

Question 15

Describe the procedures for assessing fetal status including diagnostic amniocentensis, chorionic villus sampling, percutaneous umbilical cord blood sampling, alpha feto protein assay and fetal monitoring.

Answer 15

amniocentensis: retrieving amniotic fluid

chorionic villus sampling: as early as 7 weeks; detects chromosomal abnormalities

percutaneous umbilical cord: blood sample from umbilical vein