Placenta (Week 7--Metten) Flashcards
What is the placenta?
Organ that has contributions from both baby and mom and connects baby to uterine wall
Allows exchange of nutrients, respiration, hormones during development
Inner cell mass
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
2 layers of trophoblast
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
How many sperm in one shot?
150 - 600 million sperm (1 tsp - 1 Tbsp)
Note: only 50 to 100 make it to the egg
When do you get blastocyst?
End of 1st week
Note: zona pellucida must degenerate in order for blastocyst to implant (does this while morula/blastocyst forming)
How is the primary yolk sac formed?
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
Where does the chorionic cavity come from?
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
Amniocentesis
For prenatal diagnosis of chromosomal anomalies
Performed at 16 - 20 weeks gestation
Remove sample of 20cc fluid from amniotic cavity using ultrasound guidance (invasive)
What happens in the second week to allow mother’s capillaries to communicate with fetus?
Maternal capillaries in endometrial stroma (decidua) expand and form sinusoids that anastomose with lacunae in syncytiotrophoblast
Mom can have blood spotting when this happens
Primary chorionic villi
Cytotrophoblast covered by syncytiotrophoblast
Secondary chorionic villi
Extraembryonic mesoderm surrounded by layer of cytotrophoblast covered by syncytiotrophoblast
Tertiary chorionic villi
Extraembryonic mesoderm with capillaries (baby’s capillaries!) surrounded by layer of cytotrophoblast cells covered by syncytiotrophoblast
(end of week 3)
Components of the placenta
Decidua is mom’s endometrial stroma
Intervillous space (trophoblast lacunae that expand then coalesce; lined by syncytiotrophoblast)
Chorionic plate (chorionic villi and baby)
Syncytiotrophoblast
Umbilical cord
Connecting stalk and vitalline duct wrapped in amnion
Contains umbilical arteries (baby to placenta), umbilical vein (placenta to baby), Wharton’s jelly (connective tissue)
Cotyledon
As placenta matures, basal plate (mother) sends septum down to separate villi (hanging off chorionic plate–baby) and get mounds of tissue called cotyledons
What layers do nutrients, gases, waste have to go through to exchange from mom’s blood to baby’s blood? (Placental barrier)
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)
How does the decidual tissue form?
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
Events leading up to mom and baby’s blood being able to exchange nutrients
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)
What bad things can get through the placental barrier?
Viruses (HIV)
Toxins (alcohol)
Drugs
What happens during the 8th and 9th weeks?
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)
Chorionic villus sampling (CVS)
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
Decidual tissue different names depending on where it is
Decidua basalis: between fetus and uterine muscular wall
Decidua capsularis: superficial decidual tissue overlying fetus
Decidua parietalis: remaining tissue (completes circle with decidua basalis)
What eventually happens to the decidua capsularis?
Villi under decidua capsularis degenerate to form smooth chorion, so it essentially fuses with decidua parietalis
Chorion frondosum (vilous chorion)
Villi near decidua basalis proliferate and enlarge to form chorion frondosum
Now, placenta is called placenta basalis
Amniochorionic membrane
Amnion fuses with smooth chorion
This is what ruptures at onset of labor and lets out amniotic fluid (water breaks)
Placenta previa
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
What is expelled as afterbirth?
30 minutes after birth:
Placenta
Embryonic membranes
Remainder of umbilical cord
Much of maternal decidua (functional layer of endometrium)
