Placenta Flashcards
Where does the embryo receive its early nutrition from?
Diffusion through zona pellucida
Blastocyst fluid
Yolk sac
Where does the foetus receive its long term nutrition from?
Maternal circulation (from day 12 - term)
Where do ectopic pregnancies most commonly occur?
Uterine tubes
What is an ectopic pregnancy?
Implantation outside of the uterine cavity
What can ectopic pain be mistaken for?
Appendicitis
What is the decidua?
Endometrium once it has undergone changes due to pregnancy hormones
What are the 3 layers of the decidua?
Decidua Basalis (under the blastocyst) Decidua Capsularis (covering blastocyst) Decidua Parietalis (remainder of uterine lining)
Which part of the decidua forms the maternal placenta?
Decidua Basalis
What are the functions of the placenta?
Endocrine (HCG, progesterone, oestrogen)
Transfer (for nutrition and waste)
Immunity (IgG antibodies able to cross easily)
What are the key foetal membranes?
Chorion
Amnion
[But also yolk sacs and allantois]
What is the key contents of the umbilical cord?
2 x umbilical arteries
1 x umbilical vein
Surrounded by Wharton’s jelly
What should you check when cutting the umbilical cord after birth?
Presence of 2 umbilical arteries - having only one artery could lead to CV defects
When do lacunae networks form?
Days 10-12
How do lucanae networks form and what is their function?
Fusion of adjacent lacunae to form networks in the syncytiotrophoblast
Maternal spiral arteries and veins open into lacunae and is returned via endometrial veins - nourish the embryo by diffusion
How and when do chorionic villi form?
Week 2 = cells from cytotrophoblast grow into syncytiotrophoblast forming primary chorionic villi
From week 3 = extraembyronic mesenchyme grows into primary villi forming secondary villi
Week 3 = blood vessels develop in extraembryonic mesoderm and communicate with the umbilical vessels forming tertiary villi
How does placental anchoring occur?
Cytotrophoblast grows through and surrounds syncytiotrophoblast forming a shell with chorionic villi attached (anchoring the villi) - shell attaches to decidua basalis
What happens to the placental membrane throughout gestation and what is the clinical relevance of this in post-date pregnancies?
Gets thinner to cope with increasing nutritional demand
Post-date pregnancies may result in placenta not being able to keep up with demand
What is placental accreta?
Uncontrolled invasion of the placenta into the myometrium of the uterus - can result in placenta not detaching properly at birth increasing risk of post-partum haemorrhage
What is placental percreta?
Most severe form of placental accreta in which the chorionic villi invade the perimetrium of the uterus - can result in placenta not detaching properly at birth significantly increasing risk of post-partum haemorrhage
What is placental previa?
Occurs when the placenta lies low in the uterus and partially or completely covers the cervix - increases risk of haemorrhage during late pregnancy, labour or delivery due to risk of placenta separating from the uterus wall as cervix begins to dilate
What is placental abruption?
Placental separation from the uterine wall during pregnancy resulting in subplacental haemorrhage
What is inadequate placentation?
Failure of normal invasion of trophoblast cells leading to maladaptation of maternal spiral arterioles and poor uteroplacental blood flow (pre-eclampsia)
What is the embryological remnant of the allantois?
Urachus (on bladder)
What makes up the chorion membrane?
Syncytiotrophoblast
Cytotrophoblast
Extraembryonic mesoderm
