17 - Placenta "BB to Basketball"

Question 1

The placenta is a fusion between the ______ and ______ tissue for the purpose of _______.

Answer 1

Fetal (chorion) and maternal (endometrium) tissue for metabolic exchange.

Question 2

What are three words that describe the placenta?

What is it’s size?

Answer 2

Transient, vital, and changing.

2-3 cm X 15-20; ~550 g

Question 3

_______ mediates implantation, ______ formed more ______ until the blastocyst is completely implanted.

Answer 3

Syncytiotrophoblast mediates implantation.

Cytotrophoblast forms more syncytiotrophoblast.

Question 4

What occurs as implantation continues? When is the embryo completely embedded?

Answer 4

The syncytiotrophoblast continues to expand and the uteroplacental circulation is established.

Completely embedded by day 12-14.

Question 5

Describe the two tissues formed by the expanding trophoblastic tissue?

Answer 5

Chorionic plate: chorion adjacent to the embryo

Cytotrophoblast shell: trophoblast adjacent to the decidua basalis.

Question 6

What saves the corpus luteum from shedding during implantation?

Answer 6

Human chorionic gonadotropin (hCG).

Question 7

What sheds during menses? What other tissues are in the uterus?

Answer 7

Decidual tissue is shed during menses.

Deep to the decidual tissue is the compact tissue, and deeper to that is the spongy tissue, and then the myometrium.

Question 8

How are the regions of the decidua named? Name the types of decidua.

Answer 8

In reference to the embryo.

D basalis: at site of implantation

D capsularis: surrounding the embryo

D parietalis: remainder of deciduating endometrium that doesn’t participate in implantation.

Question 9

What is thechorion? What forms from the chorion?

Answer 9

Trophoblast [cyotrophoblast and syncytiotrophoblast] + extraembryonic mesoderm.

Chorionic (placental) villi.

Question 10

What happens to the myometrium during implantation?

Answer 10

Contractions become quieted with smooth muscle mitosis.

Question 11

What are primary chorionic villi?

Answer 11

Extensions of cytotrophoblast into the syncytiotrophoblast.

Question 12

What is the structure of secondary chorionic villi?

Answer 12

They acquire a core of extraembryonic mesodern.

Question 13

What is the structure of tertiary chorionic villi?

Answer 13

They have blood vessels in their core.

Question 14

On what days of embryonic development are primary, secondary, and tertiary chorionic villi formed?

Answer 14

Primary - 14

Secondary - 16

Tertiary - 21

Question 15

As tertiary chorionic villi grow, what distinct regions can be identified?

Answer 15

Stem (anchoring) villi

Intermediate (free) villi

Terminal villi

Question 16

What is the function of stem villi? What are the central vessels?

Answer 16

Provide central support for the villous tree.

Solid extension of cytotrophoblast that extends distally through the syncytiotrophoblast and expands adjacent to the decidua, contributing to the cytotrophoblastic shell.

Central vessels are arteries and veins.

Question 17

What is the structure of intermediate villi (branches of the villous tree)? What are the central vessels in them?

Answer 17

They float in the intervillous space; the central vessels are arterioles, venules, and capillary loops.

Question 18

What is the structure of terminal villi (small branches on the intermediate villi)?

Answer 18

The central vessels are sinusoids (larges capillaries).

Question 19

Whose blood cells are located in the core of tertiary chorionic villi? What surrounds the villous tree structure?

Answer 19

Blood cells of the baby.

Branches of the villous tree are bathed in maternal blood contained within the intervillous spaces.

Question 20

What allows the placenta to separate from the endometrium? Name each component and its role.

Answer 20

Basal plate: functional zone of endometrium and chorionic tissue, the basal plate separated with placenta at birth.

Placental base: basal zone of endometrium in decidua basalis; remains in the uterus after birth.

Question 21

What are two regions of the chorion that get their named change? Why does this occur?

Answer 21

D Capsularis: chorion loses villi here and is now called the chorion laeve (smooth chorion).

D Basalis: Chorion here retains villous and is now called chorion frondosum (villous chorion).

Question 22

What are the two components of the placenta and what is each derived from?

Answer 22

Chorion frondosum (from embryo) and the decidua basalic (from mom)

Question 23

What is a codyledon?

Answer 23

A placental lobe that contains hypertrophied tertiary villi, located between 2 placental septa.

Question 24

What does placental circulation provide? Where does this occur?

Answer 24

An exchange of substances between maternal and fetal blood.

Intervillous spaces become an arterio-venous anastomosis for maternal blood.

Question 25

What brings oxygenated blood to the placenta? What brings deoxygenated blood back to the mom?

Answer 25

Umbilical vein beings oxygenated blood to baby.

Placental arteries bring deoxygenated blood back to mom to be oxygenated.

Question 26

During week 3-4, blood vessels that connect the chorion and the embryo form what?

Answer 26

The connecting stalk.

Question 27

Describe the initial placental membrane? How does this change after month 4?

Answer 27

Syncytiotrophoblast, cytotrophoblast, basement membrane, extraembryonic mesoderm, capillary endothelium.

After month 4: loss of cytotrophoblast, thinning of syncytiotrophoblast, decrease in size of chorionic villi. Some mixing of maternal and fetal blood (usually insignificant).

Question 28

What are the three functions of the placenta?

Answer 28

1. Mediates transport and metabolism of nutrients and wastes
2. Secretes essential proteins and hormones
3. Protects the embryo/fetus from immunological attack

Question 29

What are three ways that materials can cross the placental barrier? What are examples of materials that can do this?

Answer 29

Diffusion, endocytosis, and exocytosis.

Drugs, chemicals, and infectious agents (particularly in the latter stages of pregnancy).

Question 30

What are three things that the placenta secretes?

Answer 30

Peptide hormones (those that the pituitary would normally secrete), steroid hormones, and placental proteins.

Question 31

Since the fetus is an allograph (genotype different from mom), why isn’t the embryo rejected? Give three possibilities.

Answer 31

1. Surface of syncytiotrophoblast has no paternal histocompatibiltiy antigens (no warning signs).
2. Maternal immune system is selectively suppressed
3. The decidual reaction sets up an immunologically privileged site for the embryo/fetus.

Question 32

What are the two faces of the placenta? What side faces the fetus?

Answer 32

1. Fetal (shiny) side

2. Maternal (muddy) side that faced the basal zone of the endometrium. Codyledons are visible.

Question 33

What is placenta previa? What does it cause?

Answer 33

Implantation near the internal cervical os.

Causes premature detachment with hemorrhaging.

Question 34

What is placenta accreta? What problem can this cause?

Answer 34

Implantation of placenta that extends into the basal zone.

Can cause incomplete delivery of the placenta that may require a hysterectomy if it can’t be detached.

Question 35

What is abruptio placenta? What can it cause?

Answer 35

Detachment of the placenta resulting from hemorrhage into the decidua basalis separating the junctional zone.

Can cause decidual necrosis and placental infarcts.

Question 36

What are potential causes of abruptio placenta?

Answer 36

Maternal malnutrition, smoking, hypertension, trauma, and drug abuse.

Question 37

What is a complete molar pregnancy?

Answer 37

Only paternally derived DNA present, a definite malignancy risk.

Mass of chorionic vessels with no embryo.

Question 38

What is an incomplete molar pregnancy?

Answer 38

Maternal and paternal DNA present.

The phenotype of any embryo present depends on the maternal/paternal DNA ratio.

Question 39

What is a hydatidiform mole? What is an indication of one? What it this an example of?

Answer 39

Trophoblast development without an embryo.

Increased hCG levels into the second month of prengancy.

Example of genomic imprinting.

Question 40

What is velamentous cord insertion?

Answer 40

When the umbilical cord attached to the chorion and amnion instead of the middle of the placenta where it belongs.

Question 41

When does the formation of the placenta begin?

Answer 41

At implantation.