Placental structure, function and abnormalities

Question 1

Where are the villi located in the early stages of pregnancy?

Answer 1

Villi are present over the entire surface of the blastocyst.

Question 2

What happens to the decidua capsularis as the blastocyst enlarges?

Answer 2

Becomes compressed, cutting off circulation, leading to atrophy and disappearance of villi associated with it.

Question 3

What is the chorion laeve?

Answer 3

The smooth surface of the blastocyst after villi disappear from the decidua capsularis.

Question 4

What is the chorion frondosum, and where is it located?

Answer 4

The region of the blastocyst where villi proliferate and enlarge, located at the opposite pole of the blastocyst.

Question 5

What occurs when the decidua capsularis meets the decidua vera?

Answer 5

The uterine cavity becomes obliterated.

Question 6

What are the two layers of the trophoblast, and what are their functions?

Answer 6

Cytotrophoblast: Cellular layer that surrounds fetal vessels.

Syncytiotrophoblast:
- invades the decidua
- destroys glands and stroma
- forming sinusoids with maternal blood vessels.

Question 7

Describe the structure of a chorionic villus.

Answer 7

Contains fetal vessels surrounded by cytotrophoblast, bathed in maternal blood, and branches into complex tree-like structures for nutrient and waste exchange.

Question 8

What is the physiological change in the maternal spiral arteries during pregnancy?

Answer 8

• Trophoblast invades the arteries
• dilating them
• converting the uteroplacental blood supply into a
• low-resistance
• high-flow vascular bed.

Question 9

What complications are associated with failure of trophoblast invasion?

Answer 9

Pregnancy-induced hypertension (PIH)

Intrauterine growth restriction (IUGR)

Question 10

How does the placental barrier facilitate transfer between maternal and fetal circulations?

Answer 10

1. thinning structures between the two circulations
2. increasing surface area via,
   - syncytiotrophoblast microvilli
   - dilating villus vessels.

Question 11

Describe the structure of the fully formed placenta.

Answer 11

• Red
• Discoid structure
• 2–3 cm thick at the umbilical cord insertion
• Weighing ~500 g at term.

Question 12

What is Wharton’s jelly, and what is its function?

Answer 12

• gelatinous substance surrounding the umbilical cord
• preventing pressure, occlusion, and twisting of the cord.

Question 13

How is the umbilical cord structured and attached to the placenta?

Answer 13

• contains two arteries and one vein
• attaches near the placenta’s center

Question 14

What are the key functions of the placenta beyond nutrient and respiratory gas transport?

Answer 14

The placenta also has endocrine functions, producing hormones and other proteins essential for pregnancy.

Question 15

How is oxygen and carbon dioxide exchanged between maternal and fetal blood?

Answer 15

By diffusion, facilitated by the unique oxygen dissociation characteristics of fetal blood.

Question 16

How is glucose transported across the placenta?

Answer 16

Through a specific transport mechanism involving an integral membrane protein

Question 17

How are amino acids transported across the placenta?

Answer 17

Via three separate mechanisms, though acidic amino acids are poorly transported.

Question 18

How do cholestrol transfer across the placenta?

Answer 18

Via endocytosis.

Question 19

Name some hormones produced by the placenta and their roles.

Answer 19

Human chorionic gonadotrophin (HCG): Stimulates adrenal and placental steroidogenesis; analogous to luteinizing hormone (LH).

Estrogen complex: Stimulates uterine blood flow and growth.

Progestogens: Enable implantation and relax smooth muscle.

Adrenocorticoids: Induce fetal enzyme systems and promote fetal maturity.

Question 20

What glycoproteins are produced by the placenta?

Answer 20

1. Pregnancy-Associated Proteins A-D,
2. Pregnancy-Specific Glycoprotein (SP1)
3. Placental Protein 5 (PP5)

Question 21

How is placental and fetal metabolism used in disease screening?

Answer 21

Alphafetoprotein (AFP): Produced by the fetal liver, gut, and yolk sac, used to screen for anatomical abnormalities.

Maternal serum HCG and AFP: Used to calculate the risk of fetal trisomy.

Question 22

From which structures are the membranes derived?

Answer 22

From the amnion and the chorion laeve

Question 23

What is the approximate length of the umbilical cord?

Answer 23

Approximately 50 cm.

Question 24

What is a bipartite placenta?

Answer 24

A placenta partly divided into two lobes with connecting vessels.

Question 25

What is a duplex placenta?

Answer 25

A placenta completely divided into two lobes, with vessels uniting to form the umbilical cord.

Question 26

What is a succenturiate placenta, and why is it clinically significant?

Answer 26

A placenta partly or completely divided into two or more lobes with vascular connections between the main and accessory lobes.

Clinical significance:
- Blood vessels between lobes may tear during labor, causing antepartum hemorrhage from fetal origin.

• High fetal mortality rate if bleeding occurs.
• Torn vessels at the membrane edge post-delivery may indicate retained accessory lobes requiring manual removal.

Question 27

What is a circumvallate placenta?

Answer 27

Membranes appear attached internally to the placental edge.

Periphery has a ring of thick whitish tissue, a fold of infarcted chorion.

Clinical significance: Associated with antepartum and postpartum hemorrhage.

Question 28

What is a battledore placenta?

Answer 28

A placenta with marginal instead of central cord insertion. It has no clinical significance.

Question 29

What is velamentous insertion of the cord?

Answer 29

The placenta develops some distance away from the cord attachment, and vessels divide in the membranes.

If vessels cross the lower pole of the chorion, vasa praevia occurs.

Clinical significance: Membrane rupture can cause fetal blood loss due to hemorrhage.

Question 30

What are placental infarcts?

Answer 30

Areas of degeneration showing hyaline and calcareous changes.

Clinical significance: Generally none unless large enough to interfere with fetal nutrition.

Question 31

What are placental tumors?

Answer 31

Definition: Extremely rare, with hemangioma being the only significant type.

Clinical significance: Often associated with polyhydramnios.