11. Placenta and Fetal Membranes (Dennis)

Question 1

What changes between the tertiary chorionic villi between early and late pregnancy?

Answer 1

The cytotrophoblasts become “attenuated” and disappear.

Question 2

Why doesn’t the placenta wrap all the way around the amniotic sac?

Answer 2

Because the superficial direction of the chorion becomes compressed by its proximity to the decidua capsularis. This causes ischemia in the chorionic villi, which then disappear. Since they aren’t there to form into the placenta, the placenta only forms where the chorionic villi contact decidua basalis.

Question 3

What is amniotic fluid made of?

Answer 3

Organic compounds like proteins, carbs, fats, enzymes, and hormones.

Inorganic salts, ions, glycol phospholipids, and steroid hormones.

Question 4

What are the three layers of the decidua and thier relative locations?

Which part of the decidua is the maternal part of the placenta?

Answer 4

Decidua basalis: deep to the conceptus.

Decidua capsularis: superficial, and overlying the conceptus.

Decidua parietalis: the remaining part of the decidua.

Question 5

How is the intervillous space formed?

Answer 5

The chorionic villi invade the decidua basalis and erode the space out.

Question 6

What happens to the placental membrane around the twentieth week?

Answer 6

The cytotrophoblastic layer is essentially lost, causing a thinning of the membrane where the syncytiotrophoblasts are in direct contact with the endothelium of the fetal capillaries.

This is called the vasculosyncytial placental membrane.

Question 7

What gives rise to the amnion?

Answer 7

The epiblast.

Question 8

What is the fetal part of the placenta?

Answer 8

The chorionic sac.

Question 9

What are the four fetal membranes?

Answer 9

The chorion.

The amnion.

The umbilical vesicle.

The allantois.

Question 10

And what two stages of development can monozygotic twins form, and what implication does this have for the placenta, chorionic sac, and amniotic sac?

Answer 10

Monozygotic twins which separate in the two cell stage to the Morrill stage will have two separate chorionic sacs, two separate placentas, two separate amniotic sacs.

Monozygotic twins which separate in the embryoblast stage result in one placenta, one chorionic sac, but still two amniotic sacs.

Question 11

What is the clinical significance of oligohydramnios?

Answer 11

Leads to problems with fetal development such as renal a Genesis, pulmonary hypoplasia, and underdevelopment of the G.I. tract.

May be due to a placental abnormality or maternal high blood pressure.

Question 12

Explain the formation of the amnion.

Answer 12

The embryoblasts, in the stages before the bilaminar disc, develops a primordial amniotic cavity. Soon, angiogenic cells called amnioblasts develop finish the formation of the amniotic cavity.

Question 13

What is the difference between primary, secondary, and tertiary chorionic villi?

Answer 13

Primary chorionic villi have a cytotrophoblast core covered by syncytiotrophoblasts.

Secondary chorionic villi contain some mesoderm in the middle of a ring of cytotrophoblasts, which itself is in the middle of a ring of syncytiotrophoblasts.

Tertiary chorionic villi have true blood vessels inside of the ring of cytotrophoblasts inside of the ring of syncytiotrophoblasts.

Question 14

What makes up the fetal part of the placenta?

Answer 14

The villous chorion.

Question 15

What sorts of hormones can cross the placenta?

Answer 15

Nonprotein hormones, such as steroid hormones and thyroid hormones.

Question 16

What is at the core of the chorionic villi?

Answer 16

Mesenchymal connective tissue and fetal blood cells.

Question 17

What are the two basic causes of a hydatidiform mole?

Answer 17

Partial mole: meiotic nondisjunction or two haploid fertilizing sperm.

Complete mole: fertilization of a nonviable ovum by haploid sperm.

Question 18

What is placenta previa?

Answer 18

When the placenta attaches too close to, or over, the cervical opening.

Can be marginal, partial, or total.

Question 19

What are syncytial knots?

Answer 19

Aggregate – very eosinophilic – nuclei of syncytiotrophoblasts that are deposited at random, but often found on the surfaces of villi.

– These are markers of late stage pregnancy. –

Question 20

What is an anchoring villi?

Answer 20

A chorionic villus that attaches to the maternal tissues through the cytotrophoblastic shell.

Question 21

What is the primordial uteroplacental circulation?

Answer 21

The phenomenon by which oxygen and nutrients are passed into the developing embryo via diffusion through the liquor networks in the syncytiotrophoblasts (chorionic sac).

Question 22

What is contained within the umbilical cord?

Answer 22

Two umbilical arteries and one umbilical vein.

Question 23

Where does amniotic fluid come from?

Answer 23

Maternal tissue and interstitial fluid.

Question 24

What is bypassed by the ductus venosus?

Answer 24

The liver.

Question 25

The intervillous spaces between which two layers of the placenta?

Answer 25

Between the decidua basalis and the chorionic plate.

Question 26

Where does hCG come from before it enters maternal blood?

Answer 26

The syncytiotrophoblasts.

Question 27

What structures make up the chorionic sac?

Answer 27

The extraembryonic somatic mesoderm.

The cytotrophoblasts.

The syncytiotrophoblasts.

Question 28

What is the clinical significance of polyhydramnios?

Answer 28

May indicate a genetic defect in the fetus.

May indicate specifically a central nervous system defect in the fetus.

Or may indicate a blockage of the gastrointestinal tube.

Clinical signs include abdominal pain, swelling and bloating, or breathlessness.

Question 29

What sort of blood is carried within the umbilical vein?

Answer 29

80% oxygenated fetal blood from the placenta.

Question 30

What is the name of the macrophages found within the connective tissue core of the chorionic villi?

Answer 30

Hofbauer cells.

Question 31

What is placenta accreta/increta/percreta?

What are the three severities?

Answer 31

An abnormally strong and deep attachment of the placenta to the uterine wall.

Placenta accreta: placenta invades the uterine wall but does not penetrate the myometrium.

Placenta increta: placenta penetrates through the myometrium.

Placenta percreta: placenta penetrates through the myometrium and the uterine serosa, commonly attaches to the bladder and or rectum.

Question 32

What forms the placental barrier histologically speaking?

Answer 32

Cytotrophoblasts, syncytiotrophoblasts, and their supporting basal lamina.

The endothelial cells and the basal lamina of the fetal blood capillaries.

Question 33

What complication can arise from an undiagnosed hydatidiform mole?

Answer 33

Choriocarcinoma: highly invasive metastatic tumor arising from chorionic epithelium.

Question 34

What is a cotyledon?

Answer 34

A space in the decidua basalis which is separated by placental septa, and contains 2+ main stem villi and multiple branch villi.

Question 35

What sort of drugs can and can’t cross the placenta?

Answer 35

Most drugs can cross, such as alcohol, cocaine, heroin, labor-management drugs, etc.

Drugs with structural similarities to amino acids cannot cross – such as methyldopa and heparin.

Question 36

What is bypassed by the ductus arteriosus and foramen ovale in the fetus?

Answer 36

The lungs.

Question 37

What sort of infectious agents can and can’t cross the placenta?

Answer 37

As a general rule, bacteria cannot.

Most viruses can, as well as syphilis, toxoplasmosis and listeria.

Question 38

How is the interface for maternal blood flow established after implantation?

Answer 38

Syncytiotrophoblasts grow into the endometrium and contact the spiral arteries from the mother. Enzymes degrade the spiral arteries and blood rushes into the lacunae formed in the syncytiotrophoblasts.

Question 39

What is the decidua?

Answer 39

Decidua is the portion of the functional layer of the endometrium which separates from the remainder of the uterus after childbirth.

Question 40

Which antibodies can cross the placenta?

Answer 40

IgG only.