Fetal Membranes

Question 1

What are the fetal membranes

Answer 1

Chorion, amnion ,yolk sac, allantois

Question 2

What is the chorion

Answer 2

Consists of Syncytiotrophoblast, cytotrophoblast and primary mesoderm

Question 3

Primary villus

Answer 3

Cytotrophoblast core covered by Syncytiotrophoblast

Days 12-13

Question 4

Secondary villus

Answer 4

Extra embryonic mesoderm invades centre of each primary villus
Formed on day 16

Question 5

Tertiary villus

Answer 5

Fetal blood vessels grow in mesoderm forming core of each villus
Formed by day 21

Question 6

What is the fate of villi

Answer 6

In early weeks of development villi cover entire surface of chorion as pregnancy advances —chorion frondosum( bushy) 
(On embryonic pole)
Chorion leave(smooth) due to degeneration of villi opposite decidua capsularis

Question 7

CLINICAL CORRELATION

What is a hydatidform mole

Answer 7

Trophoblast develops and forms placental membranes and little or no embryonic tissue is present
Could be benign or cancerous

Question 8

What is preeclampsia

Answer 8

Insufficient invasion of trophoblast cells in to mymoterial portion of spiral arteries
So utero placental vessels fail to provide sufficient blood to supply to placenta
Hypoxia
Resulting in hypertension

Question 9

What is amnion

Answer 9

Small cavity within epiblast
Cell enlarges to become amniotic cavity filled by amniotic fluid
As embryo folds amniotic cavity expands greatly and surrounds embryo on all sides

Question 10

Sources of amniotic fluid

Answer 10

Maternal blood
Amniotic cell membranes
Fetal urine

Question 11

Composition of amnion

Answer 11

Clear watery fluid containing 2% salts enzymes and hormones

Question 12

What are the functions of amniotic fluid

Answer 12

▪️Protects embryo from shocks
▪️Prevents adhesion of amniotic membrane to the growing embryo
▪️Allows free movement of embryo to ▪️permit muscular growth
▪️Permits external env for growth of embryo
▪️Teaches baby how to suckle
▪️Keeps temperature constant

Question 13

Name the Abnormalities related to amniotic fluid

Answer 13

Polyhydraminos: volume exceeds 1.5-2 liters
Could be due to anencephaly,esophageal Artesia or maternal diabetes

Oligohydraminos: volume less than half a liter
Could be due to renal agensesis or placental insufficiency

Caul de sac: fetus is delivered with amniotic membrane intact

Question 14

What is the yolk sac

Answer 14

Flattened cells originating from hypoblast form thin membrane —exocoelmic membrane that lines inner surface of Cytotrophoblast
Together with hypoblast form lining of primitive yolk sac

Question 15

How is secondary yolk sac produced

Answer 15

Hypoblast produces additional cells that migrate along the inside of excocelmic membrane which forms a new cavity
Smaller than primary

Question 16

What are the functions of the yolk sac

Answer 16

▪️Endoderm gives mucous membrane of GIT, respiratory system and most of urinary bladder
▪️primordial germ cells present in wall of yolk sac migrate to site of ovary and testis to form ova and sperms

Question 17

What are abnormalities related to the yolk sac

Answer 17

▪️Foecal umbilical hernia: due to persistence of yolk sac
▪️Meckel’s diverticulum: due to persistence of a part of yolk sac attached to intestine(2 inches long 2 feet away from ileocaecal junction)
▪️fibrous band: yolk sac obliterates and is changed in to fibrous band which may lead to intestinal obstruction
▪️vitelline sinus and cyst

Question 18

What is the allantois

Answer 18

When cloacal membrane appears the posterior wall of the yolk sac forms a small diverticulum that extends to the connecting stalk

Question 19

What are the functions of the allantois

Answer 19

Primary mesoderm of connecting stalk surrounding allantois gives umbilical blood vessels

Question 20

What is the fate of the allantois

Answer 20

Intraembryonic part obliterates to give the uracus which persists as median umbilical ligament after birth

Question 21

What are the abnormalities of allantois

Answer 21

Urachal syst
Urachal sinus
Urachal fistula