Placenta Flashcards
Where does the early blastocyst get its nutrition?
1) Diffusion through zone pellucida
2) Blastocyst fluid
3) Yolk sac
Where does long-term nutrition for the foetus come from? And when does this occur?
Long-term nutrition comes from the maternal circulation.
This happens from around day 12 until full term
At what day(s) does the embryo become a blastocyst?
Day 4-5
At what day(s) does the blastocyst hatch out of the zone pellucida and stick to the endometrium?
Day 6-7
What happens at day 4-5
Morula becomes an early blastocyst
What happens at day 6-7?
the blastocyst hatches out of the zone pellucida and stick to the endometrium
What is the decidual reaction/decidualisation? And when does this occur?
The cellular and vascular changes occurring in the endometrium as the blastocyst implants and triggers the start. Occurs at Day 7.
Define decidua
Decidua is the functional layer of the endometrium of a pregnant woman that separates from the remainder of the uterus after parturition (childbirth).
What happens at day 7?
Decidualisation - start of implantation. Syncytiotrophoblast invades endometrium and into uterine glands.
What two cell types does the trophoblast differentiate into?
Syncytiotrophoblast and cytotrophoblast
What are the uterine glands?
They are found in the endometrium and have accumulated glycogen and lipids for the blastocyst in response to progesterone build up. As syncytiotrophoblast fingers invade into uterine glands, it provides nutrition for early blastocyst.
What is the syncytiotrophoblast?
Syncytiotrophoblast is a multinucleate invasive cell mass, which erodes into the endometrium and produces HCG early on which maintains the corpus luteum.
Through what methods does the syncytiotrophoblast invade the endometrium?
Through apoptosis and proteolysis.
What happens on day 9?
The blastocyst finishes implanting into the endometrium.
Lacunae appear within the syncytiotrophoblast. Maternal blood vessels expand near these spaces.
What happens on day 13?
The surface epithelium reforms over implanted blastocyst.
Syncytiotrophoblast forms a network of interconnected lacunar networks, invading the endometrium and eroding into the maternal blood vessels. Enlarged uterine spiral arteries connect and fill the lacunae.
Cytotrophoblast has proliferated and begun to form primary villi.
Why is lacunar fluid important at Day 13?
Lacunar fluid provides nutrition by diffusion for early embryo.
What are the 3 regions of the decidua?
Decidua basalis
Decidua capsularis
Decidua parietalis
What is the decidua basalis?
The part of the decidua deep to the blastocyst which eventually forms the maternal part of the placenta.
What is the decidua capsularis?
The superficial part of the decidua overlying the blastocyst
What is the decidua parietalis?
The remaining parts of the decidua (not the decidua basalis or capsularis)
What is the maternal component of the placenta?
Decidua basalis
What happens to the chorionic villi facing the decidua capsularis?
Chorionic villi facing the decidua capsularis undergo atrophy, resulting in the formation of the smooth chorion.
Where does ovulation occur?
Ovulation occurs into the peritoneal cavity
What type of ectopic pregnancy is the most frequent?
Tubal pregnancy (ampulla or isthmus)
What can ectopic pain mimic?
Appendicitis
What group of cells in the early blastocyst actively erode into the maternal endometrium during the implantation process?
Syncytiotrophoblast
What are the functions of the placenta?
Acts as an exchange barrier
Hormone production: Endocrine-steroid and peptide
- HCG
- Progesterone (HPO suppression)
- Oestrogen
Transfer- Nutrition
Affected by molecular weight, solubility & charge
- Simple diffusion
- Facilitated diffusion
- Active transport
- Pinocytosis / transcytosis
Immunity
- Most IgG antibodies easily cross over (passive immunity)
- IgG in fetal circulation exceeds concentration in maternal circulation as term approaches
Describe primary chorionic villi formation. When does this occur?
Cells from cytotrophoblast grow into syncytiotrophoblast
Form primary villi (finger like projections, and are thick)
Happens in week 2
Describe secondary chorionic villi formation. When does this occur?
Extraembryonic mesoderm grows into primary villi forming secondary villi.
Happens in week 3
Describe tertiary chorionic villi formation. When does this occur?
Blood present in fetal vessels by end of week 3
Tertiary villi are bathed in an extensive network of lacunae (pockets of maternal blood)
Maternal blood communicates with umbilical artery & vein
Happens in week 3
Extraembryonic mesoderm grows into the cytotrophoblasts secondary villi. The cytotrophoblasts grow through the syncytiotrophoblast and form a shell. Some villi anchor to this and form anchoring villi.
Describe placental anchoring. When does this happen and why is it important?
Cytotrophoblast grows through & surrounds Syncytiotrophoblast forming a shell
A number of tertiary chorionic villi attach to shell as anchoring villi
Shell attaches to decidua basalis
Happens in week 3.
Important to maintain integrity of placenta and proper implantation and exchange of nutrients.
Which layer of the endometrium should the placenta anchor into?
Basal (aka junctional zone) endometrium
Which membranes form the chorion?
1) Extraembryonic mesoderm
2) Syncytiotrophoblast
3) Cytotrophoblast
How does the placental (veto-maternal) membrane change throughout gestation?
Becomes thinner to cope with growing demand
14 weeks – 40 µm 22 weeks – 22 µm 38 weeks – 5 µm Placental capacity may be exceeded in post date pregnancies
What are the layers of the placental (feto-maternal) membrane before 20 weeks?
x4 layers since cytotrophoblast is continuous
1) Maternal blood
2) Syncytiotrophoblast
3) Cytotrophoblast
4) Fetal capillary endothelium/wall (+mesenchyme)
What are the layers of the placental (feto-maternal) membrane after 20 weeks?
The cytotrophoblast degenerates and is nearly absent by 20 weeks
1) Maternal blood
2) Syncytiotrophoblast
3) Cytotrophoblast (few remain)
4) Fetal capillary endothelium/wall (+mesenchyme)
What is arborisation?
Arborisation results in a massive expansion of placental surface area
The thinning of the placental barrier is essential to help meet the expanding needs of the developing foetus.
What things can go wrong with the placenta?
Position / Development:
e.g. Ectopic, accreta, percreta, previa, abruption
Growth:
e.g. Uncontrolled, gestational trophoblastic disease, choriocarcinoma
Transport unwanted substances/pathogens:
e.g. drugs, smoke, virus
Blood flow compromised:
e.g. inadequate placentation & pre-eclampsia
What is placenta praevia?
Placenta attaches near or over cervical opening
What is placenta accreta?
Invasion of outer myometrium smooth muscle
What is placenta percreta?
Invasion of outer myometrium smooth muscle - deeper than accreta
What is placental abruption?
Placental separation from uterine wall with sub placental haemorrhage
Give some examples of unwanted substances that can travel the placenta
1) Compounds from smoking
2) Drugs eg. cocaine
3) Alcohol - fetal alcohol syndrome
4) Infectious agents eg. rubella
5) Antibodies eg. rhesus
Describe some placental blood flow problems
1) Inadequate placentation Pre-eclampsia – failure of normal invasion of trophoblast cells leading to maladaptation of maternal spiral arterioles and poor uteroplacental blood flow 2) Impairment Maternal vascular disease Gestational age - post dates 3) Mechanical IVC compression (if mom sleeps on their back) 4) Volume Maternal haemorrhage / hydration
What cell layer of the implanted blastocyst grows through and surrounds the syncytiotrophoblast to form a shell, which some of the tertiary villi will anchor to?
Cytotrophoblast
What happens to the fetal membranes in late pregnancy?
Amnion and chorion fuse (chorionic cavity is obliterated)
Decidua capsularis and decidua parietali join (uterine cavity mostly obliterated)
What is found in the umbilical cord?
2 Arteries (Low O2), 1 vein (High O2), Wharton’s Jelly, and Amnion Cover
What are the three shunts found in fetal circulation?
1) Ductus venous - allows blood from the placenta to bypass the liver
2) Ductus arteriosus - allows blood to bypass developing lungs
3) Foramen ovale - allows blood to bypass developing lungs
What are cotyledons?
The cobblestone like appearance - these villi project into the maternal surface.
What does the fetal surface of the placenta look like?
Smooth and shiny because it is covered in amnion.
Unlike the maternal surface which has a cobblestone appearance and has cotyledons.
