Placental Development Flashcards
5 reasons why a baby might be small
Prematurity Infection (like CMV) Genetic Constitutional (small parents = small babies) Uteroplacental
3 uroplacental reasons for a small baby
Smoking
Maternal disease
Abnormal placentation
How far does the placenta invade normally?
Into 1/3 of the myometrium
Hemochorial
Means the placenta is formed from 2 genetically distinct people
Maternal blood is in DIRECT contact with fetal CELLS (trophoblasts)
Implantation requires 2 synchronous processes
Uterine preparation (decidual reaction) Embryo development and the ability to interact with the endometrium
Uterus
1. Proliferative
2. Secretory
Phases
- Ovarian follicles secrete estrogens causing endometrium to proliferate and remodel
- Increased levels of progesterone from corpus luteum stimulate thickening of the endometrium and forms glandular structures add increased vascularity to support an implantation
How long is the endometrium receptive to a blastocyst for?
8-10 days after an LH surge (6-7 days after ovulation)
Changes to the endometrium during implantation
Increase in cell size, change in cell shape, extensive development of intracellular organelles for protein synthesis and secretion, formation of intracellular junctions
Lipid and glycogen accumulation for energy
Where in the uterus does the placenta usually implant?
The fundus
Placenta previa
When the placenta implants over the cervix
What structures form by day 5 of embryonic development? (3)
The inner cell mass (embryonic pole), blastocoel (fluid filled cavity), and outer cell mass (trophoblast)
Trophoblasts become what 2 cell types
Cytotrophoblasts (then into villus and extravillus types)
Syncytiotrophoblasts (formed by fusion of cytotrophoblasts and invade the endometrium)
Extravillous cytotrophoblasts
Invade the maternal spiral arteries
Remodel the maternal blood vessels in the placenta
By the third trimester they allow for an open low resistance way for the blood to flow (critical to development)
How are spiral arteries remodelled?
By extravillous cytotrophoblasts
Converts a tight, thick walled muscular vessel into an open capacitance vessel that can accommodate the tremendous increase in maternal blood flow required to adequately nourish the placenta and fetus
Pre-eclampsia
Shallow cytotrophoblast invasion
Don’t get the wide open capacitance vessels in the placenta that you need
Hypertension
Some abnormalities that can arise from shallow invasion
Growth restriction Prematurity Abruptio placenta (separates before its meant to) Preeclampsia Stillbirth
Placenta accreta
When there is pathologic deep invasion of the myometrium
Risk factors: prior C section (can implant into the scar) or placenta previa
Often undiagnosed until delivery and can lead to postpartum hemorrhage, hysterectomy, and even death
The process of placental maturation includes…
Extensive branching of villi
Increased surface area available for exchange between mom and fetus
Closer approximation of maternal and fetal circulation
Increased uterine blood flow
Placenta is bigger than the fetus until ___ weeks
16
The villi in early pregnancy have __ layers. What are they?
3 layers Syncytiotrophoblasts Cytotrophoblasts Fetal capillary endothelium Also technically some CT for support
The villi in later pregnancy have __ layers. What are they?
2 layers
Syncytiotrophoblasts
Fetal capillary endothelium
This is to decrease the distance between maternal and fetal circulations
Vessels also move to a more peripheral location (closer to the blood) and the villi become more branched and vascular
Uterine blood flow at term is approximately…
700 mL per minute
Antepartum hemorrhage can be due to…
Placenta previa Abruptio placenta (can be chronic or acute)
Postpartum hemorrhage
From uterine atony (failure of the uterine muscle to contract after delivery, so spiral arteries do not get squeezed shut)
