L5: Fetal membranes

Question 1

What is the definition of fetal membranes?

Answer 1

Structures derived from the fertilized ovum and not share information of embryo.

Question 2

What are examples of fetal membranes?

Answer 2

1) Amnion.
2) Yolk sac.
3) Allantois.
4) Chorion.
5) Placenta.
6) Connecting stalk and umbilical cord.

Question 3

What is the definition of the amnion?

Answer 3

a sac filled with fluid that surrounds the embryo and fetus.

Question 4

What is the time of appearance of the amnion?

Answer 4

7th or 8th day after fertilization.

Question 5

What is the definition of amniotic fluid?

Answer 5

fluid fills the amniotic cavity.

Question 6

What is the function of amniotic fluid?

Answer 6

1) Allows fetal movements.
2) Allows symmetrical growth of the fetus.
3) Prevent adhesion between different parts of the fetus.
4) Control the body temperature of the fetus.
5) Barrier against infection.
6) Maintain fluid and electrolytes balance.
7) Protection against trauma and external shock.
8) During birth:
 Dilatation of the cervix due to the bulge of the bag of water that precedes the head of the fetus in the cervical canal.
 Fluid passes through the vagina when the bag rupture and acts as an anti-septic against infection.

Question 7

What is the source of amniotic fluid?

Answer 7

✓ Amnioblast cells. ✓ fetal kidney✓ Placenta.

Question 8

What is the circulation of amniotic fluid?

Answer 8

✓ Fluid accumulates in the amniotic cavity.
✓ Fetus swallows fluid and some pass to lungs and absorbed by respiratory system of the fetus and digestive tracts (fetus drink 400c.c at 5th month).

Question 9

What is the fate of amniotic fluid?

Answer 9

✓ Fluid passes to fetal blood and waste products cross the placental membrane and enter maternal blood in intervillous space.

✓ Excess water is excreted by the fetal kidney through the urinary tract back to the amniotic sac.

Question 10

What is the composition of the amniotic fluid?

Answer 10

✓ 99% water.

✓ 1% desquamated (peeled off) epithelial cells, organic constituents.

✓ Fetal excreta

Question 11

Compare between oligo and polyhydramnios Acc to

Def.
Cause
Character

Answer 11

 The volume of amniotic fluid is less than 1/2 liter.

 Placental insufficiency  Renal agenesis (absence
of one kidney)

 Fetal anomalies  Fetal adhesions.

 The volume of amniotic fluid is more than 2 liters.

 Maternal diabetes.  Fetal anomalies
 esophageal atresia (obstruction of the esophagus).

 Fetal distress.
 Maternal distress.
 A true knot of umbilical due to: excessive fetal movements.
 Premature labor.

Question 12

What is the definition of a yolk sac?

Answer 12

a cavity in relation to the ventral surface of the embryo.

Question 13

What is the time of appearance of the yolk sac?

Answer 13

It begins to appear at 2nd week after fertilization “after amniotic cavity”

Question 14

What is the fate of the yolk sac?

Answer 14

❖ Gut formation

❖ Vitellointestinal duct (obliterate but if still present will form Meckel’s diverticulum)

❖ allantois

Question 15

What are the functions of the yolk sac?

Answer 15

❖ Transfer nutrients to the embryo (in the 2nd and 3rd weeks) before the function of the placenta.

❖ (Haemo-poetic function) Development of blood cells and blood vessels first occurs in the extraembryonic mesoderm covering the wall of the yolk sac.

Question 16

What is the definition of the chorion?

Answer 16

It is the wall of the chorionic sac (gestational sac).

Question 17

What are the layers of the chorion?

Answer 17

❖ Syncytiotrophoblast: outer layer.
❖ Cytotrophoblast: middle layer.
❖ Extraembryonic mesoderm: inner layer.

Question 18

For how long do chorionic villi cover the chorionic sac?

Answer 18

Chorionic villi cover the chorionic sac until the beginning of the 8th week. (2nd month)

Question 19

What happens as the chorionic sac grows?

Answer 19

As chorionic sac grows:

 The villi associated with decidua capsularis are compressed.

 These villi degenerates produce avascular bare area (Chorion leave).

 Villi associated with decidua basalis increase in number, branch, and enlarge (Chorion frondosum).

Question 20

What are chorionic villi? And what are they separated with?

Answer 20

They are projections from the chorion to increase the surface area of exchange between the fetus and the mother, They are separated by intervillous spaces containing maternal blood.

Question 21

What is the definition of allantois?

Answer 21

Diverticulum from the caudal wall of the yolk sac into the connecting stalk.

Question 22

What does the allantois divide into after folding?

Answer 22

• Extraembryonic part

✓ Degenerates.

• Intraembryonic part
  ✓ forms the urachus which forms:
   The apex of the urinary bladder.
   Median umbilical ligament: is the obliterated distal part.

Question 23

From what is the umbilical cord formed?

Answer 23

by the elongation of the connecting stalk.

Question 24

What is the length of the umbilical cord?

Answer 24

at birth, it is about 50 cm long (the same length as the fetus).

Question 25

What are the ends of the umbilical cord?

Answer 25

It has 2 ends:
❖ the fetal end attached to the umbilicus
❖ placental end to the placenta.

Question 26

What is the structure of the umbilical cord?

Answer 26

1) Amniotic sheath.

2) Extra embryonic mesoderm of connecting stalk become loose and gelatinous (Wharton’s jelly) and surrounded by the amnion.

3) Umbilical vessels:
 Two umbilical arteries: carry non-oxygenated blood.
 Left umbilical vein: carry oxygenated blood.

4) Contains loops of the small intestine (physiological umbilical hernia):
 Exomphalos (omphalocele) results from non-reduction of the physiological umbilical hernia.

Question 27

What are the changes that happen to the umbilical cord after birth?

Answer 27

❖ Two umbilical arteries become occluded to form a medial umbilical ligament.

❖ The left umbilical vein becomes occluded to form ligamentum teres of the liver.

❖ The distal part of the allantois is obliterated to form a median umbilical ligament.

Question 28

What are the anomalies of the umbilical cord?

Answer 28

• Length:

✓ Long umbilical cord: may coil around the neck of the fetus (strangulation).

✓ Short umbilical cord: may cause early (premature) separation of the placenta.

• Number:

Double

• Attachment:

Abnormal attachment to the placenta.

• Knots:

✓ False: length of blood vessels more than umbilical cord

✓ True:
• head passes through a loop of cord, dangerous
• true knots cause fetal death.

Question 29

What are the types of chorionic villi according to structure?

Answer 29

• 1) Primary chorionic villi, formed of:

Outer syncytiotrophoblast.
Inner cytotrophoblast.

• 2) Secondary chorionic villi formed of:

Outer syncytiotrophoblast.
Inner cytotrophoblast.
extraembryonic mesoderm.

• 3-Tertiary chorionic villi, formed of:

Outer syncytiotrophoblast
extraembryonic mesoderm.
inner cytotrophoblast.
A branch from umbilical vessels