Placenta (Week 7--Metten)

Question 1

What is the placenta?

Answer 1

Organ that has contributions from both baby and mom and connects baby to uterine wall

Allows exchange of nutrients, respiration, hormones during development

Question 2

Inner cell mass

Answer 2

Becomes 2 layers to form embryonic disc by day 8–epiblast (amnion) and hypoblast (primary yolk sac)–and inside is amniotic cavity

Becomes future baby

If split at this stage, get monozygotic twins that have separate amnions but SHARE a placenta

Question 3

2 layers of trophoblast

Answer 3

1) Cytotrophoblast: mononucleated layer of cells; forms syncytiotrophoblast
2) Syncytiotrophoblast: no cell membrane, form syncytium; invade endometrial stroma, engulf decidual cells for nutrients, produce hCG to maintain CL

Question 4

How many sperm in one shot?

Answer 4

150 - 600 million sperm (1 tsp - 1 Tbsp)

Note: only 50 to 100 make it to the egg

Question 5

When do you get blastocyst?

Answer 5

End of 1st week

Note: zona pellucida must degenerate in order for blastocyst to implant (does this while morula/blastocyst forming)

Question 6

How is the primary yolk sac formed?

Answer 6

Cells migrate out to line the blastocyst cavity and it becomes the primary yolk sac

Layer of cells lining yolk sac is called Heuser’s membrane

Question 7

Where does the chorionic cavity come from?

Answer 7

Heuser’s membrane (cells lining yolk sac) secretes extraembryonic reticulum between cytotrophoblast and Heuser’s membrane

Extraembryonic mesoderm invades extraembryonic reticulum and divides it into 2 layers to form chorionic cavity

Extraembryonic mesoderm gradually separates amniotic cavity from cytotrophoblast cells

Leaves the connecting stalk to connect embryonic disc, amnion, yolk sac to outer layer

Question 8

Amniocentesis

Answer 8

For prenatal diagnosis of chromosomal anomalies

Performed at 16 - 20 weeks gestation

Remove sample of 20cc fluid from amniotic cavity using ultrasound guidance (invasive)

Question 9

What happens in the second week to allow mother’s capillaries to communicate with fetus?

Answer 9

Maternal capillaries in endometrial stroma (decidua) expand and form sinusoids that anastomose with lacunae in syncytiotrophoblast

Mom can have blood spotting when this happens

Question 10

Primary chorionic villi

Answer 10

Cytotrophoblast covered by syncytiotrophoblast

Question 11

Secondary chorionic villi

Answer 11

Extraembryonic mesoderm surrounded by layer of cytotrophoblast covered by syncytiotrophoblast

Question 12

Tertiary chorionic villi

Answer 12

Extraembryonic mesoderm with capillaries (baby’s capillaries!) surrounded by layer of cytotrophoblast cells covered by syncytiotrophoblast

(end of week 3)

Question 13

Components of the placenta

Answer 13

Decidua is mom’s endometrial stroma

Intervillous space (trophoblast lacunae that expand then coalesce; lined by syncytiotrophoblast)

Chorionic plate (chorionic villi and baby)

Syncytiotrophoblast

Question 14

Umbilical cord

Answer 14

Connecting stalk and vitalline duct wrapped in amnion

Contains umbilical arteries (baby to placenta), umbilical vein (placenta to baby), Wharton’s jelly (connective tissue)

Question 15

Cotyledon

Answer 15

As placenta matures, basal plate (mother) sends septum down to separate villi (hanging off chorionic plate–baby) and get mounds of tissue called cotyledons

Question 16

What layers do nutrients, gases, waste have to go through to exchange from mom’s blood to baby’s blood? (Placental barrier)

Answer 16

Syncytiotrophoblast

Cytotrophoblast

Fibrous tissue core (originally extraembryonic mesoderm?)

Villus (fetal) capillaries

Note: mom and baby blood does not mix! This exchange happens through intervillous space and membranes of tertiary villus (from mom’s radial arteries to baby’s capillaries in tertiary villus)

Question 17

How does the decidual tissue form?

Answer 17

When syncytiotrophoblast ate its way into stroma of functional layer of endometrium, it triggered a reaction to cause stromal cells of mom’s endometrium (especially around spiral arteries) to differentiate into decidual cells

Decidual cells are filled with glycogen and fat and are source of nutrients to blastocyst before there is blood communication

Question 18

Events leading up to mom and baby’s blood being able to exchange nutrients

Answer 18

1) Blastocyst’s syncytiotrophoblast eats its way into functional layer of endometrium
2) Triggers reaction so stromal cells adjecent to spiral arteries differentiate into decidual cells (filled with glycogen and fat)
3) Syncytiotrophoblast eats decidual cells to get nutrition to blastocyst
4) Suncytiotrophoblast gets vacuoles/lacunae and invades mom’s capillaries so mom’s blood comes into vacuoles
5) Now nutrients diffuse from mom (intervillus space) into baby (through all membranes of placental barrier)

Question 19

What bad things can get through the placental barrier?

Answer 19

Viruses (HIV)

Toxins (alcohol)

Drugs

Question 20

What happens during the 8th and 9th weeks?

Answer 20

8th week, baby called a fetus and is surrounded by amnion, the chorion, then chorionic plate with tertiary villi

9th week the placenta replaces CL as an endocrine organ (secretes E, P, hPL)

Question 21

Chorionic villus sampling (CVS)

Answer 21

Prenatal diagnosis of genetic diseases, etc

Done week 10-12

Transcervical or transabdominal, both use ultrasound guidance

Visually inspect dividing villi cells to detect chromosomal abnormalities within 3 days and tissue culture gives results in 6-8 days

Question 22

Decidual tissue different names depending on where it is

Answer 22

Decidua basalis: between fetus and uterine muscular wall

Decidua capsularis: superficial decidual tissue overlying fetus

Decidua parietalis: remaining tissue (completes circle with decidua basalis)

Question 23

What eventually happens to the decidua capsularis?

Answer 23

Villi under decidua capsularis degenerate to form smooth chorion, so it essentially fuses with decidua parietalis

Question 24

Chorion frondosum (vilous chorion)

Answer 24

Villi near decidua basalis proliferate and enlarge to form chorion frondosum

Now, placenta is called placenta basalis

Question 25

Amniochorionic membrane

Answer 25

Amnion fuses with smooth chorion

This is what ruptures at onset of labor and lets out amniotic fluid (water breaks)

Question 26

Placenta previa

Answer 26

Abnormal location of placenta over, or close to, internal os; 1 in 250 pregnancies; presents as painless bleeding usually around 30 weeks; diagnosed by ultrasound

Total: entire cervical os covered

Partial: margin of placenta extends across only part of internal os

Marginal: edge lies adjacent to internal os

Low lying: edge near but not adjacent to internal os

Question 27

What is expelled as afterbirth?

Answer 27

30 minutes after birth:

Placenta

Embryonic membranes

Remainder of umbilical cord

Much of maternal decidua (functional layer of endometrium)