Placental structure, function and abnormalities Flashcards
Where are the villi located in the early stages of pregnancy?
Villi are present over the entire surface of the blastocyst.
What happens to the decidua capsularis as the blastocyst enlarges?
Becomes compressed, cutting off circulation, leading to atrophy and disappearance of villi associated with it.
What is the chorion laeve?
The smooth surface of the blastocyst after villi disappear from the decidua capsularis.
What is the chorion frondosum, and where is it located?
The region of the blastocyst where villi proliferate and enlarge, located at the opposite pole of the blastocyst.
What occurs when the decidua capsularis meets the decidua vera?
The uterine cavity becomes obliterated.
What are the two layers of the trophoblast, and what are their functions?
Cytotrophoblast: Cellular layer that surrounds fetal vessels.
Syncytiotrophoblast:
- invades the decidua
- destroys glands and stroma
- forming sinusoids with maternal blood vessels.
Describe the structure of a chorionic villus.
Contains fetal vessels surrounded by cytotrophoblast, bathed in maternal blood, and branches into complex tree-like structures for nutrient and waste exchange.
What is the physiological change in the maternal spiral arteries during pregnancy?
- Trophoblast invades the arteries
- dilating them
- converting the uteroplacental blood supply into a
- low-resistance
- high-flow vascular bed.
What complications are associated with failure of trophoblast invasion?
Pregnancy-induced hypertension (PIH)
Intrauterine growth restriction (IUGR)
How does the placental barrier facilitate transfer between maternal and fetal circulations?
- thinning structures between the two circulations
- increasing surface area via,
- syncytiotrophoblast microvilli
- dilating villus vessels.
Describe the structure of the fully formed placenta.
- Red
- Discoid structure
- 2–3 cm thick at the umbilical cord insertion
- Weighing ~500 g at term.
What is Wharton’s jelly, and what is its function?
- gelatinous substance surrounding the umbilical cord
- preventing pressure, occlusion, and twisting of the cord.
How is the umbilical cord structured and attached to the placenta?
- contains two arteries and one vein
- attaches near the placenta’s center
What are the key functions of the placenta beyond nutrient and respiratory gas transport?
The placenta also has endocrine functions, producing hormones and other proteins essential for pregnancy.
How is oxygen and carbon dioxide exchanged between maternal and fetal blood?
By diffusion, facilitated by the unique oxygen dissociation characteristics of fetal blood.
How is glucose transported across the placenta?
Through a specific transport mechanism involving an integral membrane protein
How are amino acids transported across the placenta?
Via three separate mechanisms, though acidic amino acids are poorly transported.
How do cholestrol transfer across the placenta?
Via endocytosis.
Name some hormones produced by the placenta and their roles.
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.
What glycoproteins are produced by the placenta?
- Pregnancy-Associated Proteins A-D,
- Pregnancy-Specific Glycoprotein (SP1)
- Placental Protein 5 (PP5)
How is placental and fetal metabolism used in disease screening?
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.
From which structures are the membranes derived?
From the amnion and the chorion laeve
What is the approximate length of the umbilical cord?
Approximately 50 cm.
What is a bipartite placenta?
A placenta partly divided into two lobes with connecting vessels.
What is a duplex placenta?
A placenta completely divided into two lobes, with vessels uniting to form the umbilical cord.
What is a succenturiate placenta, and why is it clinically significant?
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.
What is a circumvallate placenta?
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.
What is a battledore placenta?
A placenta with marginal instead of central cord insertion. It has no clinical significance.
What is velamentous insertion of the cord?
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.
What are placental infarcts?
Areas of degeneration showing hyaline and calcareous changes.
Clinical significance: Generally none unless large enough to interfere with fetal nutrition.
What are placental tumors?
Definition: Extremely rare, with hemangioma being the only significant type.
Clinical significance: Often associated with polyhydramnios.
