L12: Placenta Flashcards
What weeks are for normal term pregnancy
37-42 weeks
At week 9 what is the embryo considered to be
A foetus
What is pregnancy considered to be from in terms of the date
1st of the last period
For implantation to take place what type of endometrium do we need
Receptive endometrium
When can implantation occur
Within the implantation window
Approximately when is the implantation window
In mid secretory phase
What are the 2 phases in the uterus cycle
Proliferative phase
Secretory phase
What is the proliferative phase about
Growing the endometrium
Under what hormone is the proliferative phase under the control of
Oestrogen
In the secretory phase what is the dominant hormone
Progesterone
What occurs in the secretory phases
1) oestrogen and progesterone are secreted from the corpus luteum
2) oestrogen and progesterone in moderate levels cause a negative feedback to the HPG and LH/FSH levels are suppressed
3) the progesterone matures the endometrium lining so it is receptive
4) as the corpus luteum degrades the oestrogen and progesterone levels decrease and the endometrium undergoes apoptosis so you get a period if implantation doesn’t occur
What occurs to the endometrium when it becomes receptive
Glands increase in secretions
Epithelium surface microvilli swell up (pinopodes) so they absorb the uterine fluid to help catch the blastocytes
Where does fertilisation occur
Ampulla of the uterine tube
Where does cleavage begin
In the uterine tube
At day 5 what forms
Blastocytst
At day 6 what happens to the blastocytes
Hatches from the zona pellucida
Between day8-9 what happens to the blastocytes that hatches
Implants to endometrium
What are the 3 phases of implantation
1) apposition
2) attachment
3) invasion
What occurs in apposition
Blastocyst loosely associates with the uterine wall (therefore is at risk of being washed off here)
What occurs in during attachment
Blastocyst firmly adheres to the endometrium by adhesion molecules and integrin
What happens during invasion
Blastocyst attaches to the uterine wall and triggers enzyme production which degrades and invades the glycogen rich endometrial stroma for nutrients
What is the decidua
A modified mucosal lining of the uterus the forms in preparation to pregnancy
Which hormone initiates decidualisation of the endometrium
Progesterone
What are the changes that occur in decidualisation
Oedema Blood vessels leaky Changes to extracellular matrix Angiogenesis Infiltration of uterine natural killer cells for immune tolerance for embryo Fibroblast Store glycogen and lipids Secrete proteins
At what day does the decidua surround the implanted blastocyst
Day 10
What are the 2 sides of a placenta
Embryo side
Maternal side
What are the structures in the maternal side
Chorion
Endometrial veins
Spiral arteries
How many types of placenta are there
3
What is the types of placenta based on
Structural organisation and separation of fetal and maternal blood
What are the 3 main types of placenta
1) haemochorial
2) endotheliochorial
3) epitheliochorial
Which type of placenta is found in humans
Haemochorial
What is the haemochorial
When the chorion is indirect contact with the maternal blood
As the blastocyst implants into the endometrium what happen to it
Differentiates
When the blastocyst undergoes differentiation what are the 3 main structures that form
Amniotic cavity
Bilaminar disc
Trophoectoderm (outer cell)
What is the bilmaninar disc composed of
Epiblast
Hypoblast
What are the 3 cell types the trophoectoderm gives rise to
Cytotrophoblast
Syncitiotrophoblast
Extravillous cytotrophoblast
What are the synctiotrophoblast and extravillous cytotrophast from
Cytotrophoblast
What happens to the syncitiotrophoblast
Gradually degrades its way into the endometrium tissue
What does the embryo gets its nutrients from
Products of glandular sections
Blood supply via spiral arteries
What structures then begin to form in the syncitiotrophoblast
Lucunae (spaces)
What does lucaneae store
Digested products of the cell and glands
As the syncitiotrophoblast grows into the endometrium what structure does it hit
The maternal spiral arteries
What does maternal vessel anastomose with
Lucunae
What does anastomoses of lucunae and maternal vessels from
Sinusoids
What begins the primary villi formation
When the cytotrophoblast begin to poke way down the syncitiotrophoblast between the sinusoids
What forms the primary vili
Cytotrophoblasts extend into the syncitiotrophoblast to form finger like projections into the decidua
After the primary vili what other villi begins to form/develop
Secondary villi
What occurs to from the secondary villi
Extra-embryonic mesoderm behind the cytotrophoblast begins to push the structures in between the cytotrophoblast and syncitiotrophoblast
After the secondary villi formation what villi begins to develop/form
Tertiary vili
What occurs to from the tertiary villi
1) The extra embryonic mesoderm begins to differentiate
2) formation of blood vessels from the endothelial cells
3) these blood vessel fuse with the developing vessels to link the fetal blood via invading vessels from the umbilical cord
4) sinosoidal spaces also expand so you get the formation of intervillous space
After the tertiary villi what happens to it
Matures to from the mature villi
What happens to form the mature villi
1) Stem villi form which is attached to the choronic plate
2) from the stem villi, branch vili project
3) from the branch villi, terminal villi from
Which villus is the main exchange with the maternal and fetal blood
Terminal villus
When the mature villi has developed what villus do we get
Choronic villus
What is the placental membrane
The distance of diffusion between the maternal blood and the fetal blood
What is the placental membrane like in 10 weeks of gestation
Large
What is the placental membrane large at 10weeks
The fetal blood is central placed and therefore further away from the maternal blood
When does the placental membrane decreases/shorter
At term
What allows the placental membrane to become shorter at term
More branches from
Syncitiotrophoblast thins down
Cytotrophoblast thins
Which arteries from the mother bring in maternal blood around the choronic villi
The maternal spiral arteries
Where does the maternal blood come into
The intervilous space (formed from the sinusoidal spaces)
What happens to the maternal spiral arteries to allow for low resistance and high blood flow
Remodelling to increase the diameter
Where does extravillous trophoblast form from
Cytotrophoblast at the tip of the anchoring villi
When are extravillous cytotrophoblast form
When the anchoring villi form
What happens to the extravillous cytotrophoblast when they form
- Migrate into the decidua and block the spiral arteries
- remove smooth muscle and replace endothelium to from the endovascular trophoblast layer
Why does the extravillous trophoblast cells block the spiral arteries
To create a low oxygen environment for the early foetus because it doesn’t have the mechanism to deal with oxidative stress yet
At the end of which week does the extravillous trophoblast break down the plug in the spiral arteries to allow blood flow into the intervillous space
14
Describe how remodelling of the spiral arteries occurs via extravillous trophoblast cells
1) interstitial EVT communicates with smooth muscles cells so they undergo apoptosis
2) interstitial EVT remodels the matrix and lays down material to from the scaffold support
3) endovascular EVT comes down inside the blood vessel to allows endothelial cells to undergo apoptosis
4) endovascular and interstitial EVT then replaces the endothelial cells.
Overall what does the remodelling allow
Blood vessels that are larger in diameter, low resistance and high blood flow
What are the 2 phases of nutrition for the embryo/foetus
1) histiotrophic phase
2) haemotrophic phase
What is the histiotrophic phase
Fetus gets nutrients form the glandular secretion of endometrium and breakdown of products of decidua
What is the haemotrophic phase
EVT plugs off the spiral arteries and blood flows into the placenta
How does deoxygenated blood flow from the fetus to the placenta for exchange
1) umbilical arteries
2) fetal capilaries
3) choronic villus
4) stem villus
5) intermediate villi
6) terminal villi
Which molecules can pass by diffusion across the placenta
Oxygen Carbon dioxide Sodium Urea Fatty acids Sugars
Which molecules need active transport across the placenta
Amino acids
Iron
Calcium
Which substances are not transport across the placenta
Conjugated steroids
Most bacteria
What are the harmful substances that can cross the placenta
Drugs
Caffeine
Alcohol
Cocaine
What allows the fetus to pick up the oxygen from the mother with a higher affinity
Fetal haemoglobin
What effects occurs to allow the gas exchange
Double Barr effect
What is the double Barr effect
Carbon Dioxide from fetus is dumped to maternal blood so oxygen dissociates from mother
What channels allow the diffusion of glucose across the placenta
GLUT1
GLUT3
How are protein tranported to the fetus
1) proteins are broken into amino acids
2) amino acids transported take it up
What does amino acids transporters require
ATP
What hormone is amino acids transporter on fetus regulated by
Progesterone
Which maternal antibodies can be transported to the fetus
IgG
What is early onset pre-eclampsia
Insufficient penetration of EVT and lack of remodelling of the spiral arteries so spiral arteries have small diameter and therefore low blood flow when the spiral arteries unplug
What can premature loss of EVT in spiral arteries lead to
Early initiation of blood flow that leads to miscarriage
What is the treatment of pre-eclampsia
Delivery of placenta and baby
What is intra-uterine growth restriction
When the baby does not grow as much as expected
Why does intra uterine growth restriction occur
Due to blood flow on both sides of the placenta reduced
What can intra uterine growth restriction be associated with
Pre-eclampsia
What is the normal location of implantation
High up on the posterior wall of uterus
Where else can the embryo implant that can be problematic
Marginal
Complete
Low lying
What does the marginal, complete and low lying implantation cause
Barrier to escape of uterus in parturition
Risk of placental abruption leading to haemorrhage and death of fetus
What is placenta accreta
The placenta attaches to the myometrium (deep layer) due to excessive trophoblast invasion instead of attaching to the endometrium (superficial layer)
What is the treatment for placenta accreta
- C-section of placenta
- Hysterectomy (if severe)
