Lecture 11 - Placenta Flashcards
What is the general function of the placenta?
To support the developing embryo
What are the 2 parts to the placenta?
Fetal maternal organ:
Fetal part
Maternal part
What is the fetal part of the placenta?
Part that develops from the chorionic sac that’s the outermost fetal membrane
What is the maternal part of the placenta?
Part derived from endometrium (the innermost layer of the uterine wall)
Where does fertilisation of the ovum take place?
Ampulla
What happens after the ovum get fertilised?
Mitotic divisions occur
16 cell = morula
Becomes blastocyst
Blastocyst has inner cell mass and outer cell mass
Which part of the blastocyst (inner cell mass or outer cell mass) becomes the embryo/ is called the embryoblast?
Inner cell mass
What are the cells called that make up the outer cell mass before they differentiate?
Trophoblasts
What needs to happen to the endometrial stromal cells before implantation can occur?
Decidualisation
What is Decidualisation?
The process by which stromal cells differentiate into specialised Decidual cells
What are the 2 main functions of decidual cells formed by decidualisation?
They control the depth of invasion of the trophoblasts into the endometrium
Protects the conceptus from maternal immune rejection since contains foreign DNA (Fathers)
What is considered normal implantation?
Location: upper part of uterus (fundus)
Normal invasion: within decidua (stratum functionalis)
What cells of the embryo are important in implantation?
Trophoblasts of outer cell mass
What important structures are important on the endometrium for implantation?
Pinopodes
Integrin receptors
What forms the loose connection in implantation?
Microvili of trophoblasts join to the pinopodes of the endometrium
What forms the strong connections in implantation?
Integrins on trophoblasts bin to integrin receptors on endometrium
What are the 2 connections that form in implantation?
Loose connection = microvilli on trophoblasts join to pinopodes
Strong connection = Integrins on trophoblasts join to integrin receptors
What 2 different types of cells do the trophoblasts differentiate into?
Cytotrophoblast
Syncytiotrophoblast
What is the function of the syncytiotrophoblasts?
Makes HCG to maintain corpus luteum preventing endometrium from shedding
Makes roots invading endometrium in the stroma
Makes enzymes involving invasion
What are the gaps between the invading syncytiotrophoblasts roots called?
Lacunae (fill with blood)
What is the function of the cytotrophoblasts?
They send projections through the syncytiotrophoblasts invading roots forming the Primary Villus with intervillus spaces
What is the extraembryonic mesoderm?
The layer between the cytotrophoblasts and the embryoblast/inner cell mass
The cavity the fills with fluid
What is the function of the connecting stalk?
It becomes the umbilical cord that connects the embryo to placenta
What forms the secondary villus?
The somatic layer of the extra embryonic mesoderm invades into the primary villus forming the 3 layers secondary villus
What does the connecting stalk differentiate into?
3 blood vessels
2 umbilical arteries
1 umbilical vein
What takes place to format the tertiary villus?
Chorionic vessels grow up into the villus
Umbilical vein and artery start to fill intervilous spaces
What are the cotyledons?
What forms the cotyledons?
They are groups of tertiary villi
Formed by decidual cells invaginate into the growing placenta forming septa that separate the cotyledons
What happens to the layers of the placenta as it matures?
Layers get thinner especially the Cytotrophoblast layer
To allow for material exchange
What are the 3 important embryonic sacs?
Yolk sac
Amniotic sac
Chorionic sac
What happens to the yolk sac during development?
Disappears
What happens to the amniotic sac during development?
It enlarges
What happens to the chorionic sac during development?
Lies outside the placenta and contains the expanding amniotic sac
What occurs when a woman’s water breaks?
Hole formed in the amniotic sac allowing the amniotic fluid out
What happens to the thickness of the barriers of the villi as development occurs?
Get thinner until at optimum thickness
What type of blood do the two umbilical arteries carry?
Deoxygenated blood
Where do the 2 umbilical arteries carry deoxygenated blood to and from?
Deoxygenated blood from the fetus to the placenta
What type of blood does the umbilical vein transport?
Oxygenated
Where does the umbilical vein transport oxygenated blood to and from?
Oxygenated blood from the placenta to the fetus
What is the outer transparent layer of the placenta?
Aminon membrane
What are the vessels that can be even on the outer layer of the placenta?
Chorionic vessels located under the amnion
Look at slide 20 to see what cotyledons look like
How can implantation go wrong?
Incorrect site
Incorrect depth
What is a pregnancy called that occurs outside the uterus?
Ectopic pregnancy
Why is an ectopic pregnancy not a viable pregnancy?
There’s no control in the depth of invasion of the conceptus at the site
This can lead to very deep invasion leading to haemorrhage
What is Placenta Praevia?
When implantation is too low down in the uterus leading to a low lying placenta which can cover the cervical oss
Why is placenta praevia a worrying sign?
The placenta is blood rich so if teh baby try’s to push through during child birth it could rupture leading to a massive haemorrhage = antepartum haemorrhage
What problems can occur when the implantation is too shallow?
Blood supply to placenta can be compromised
-placental insufficiency
-pre-eclampsia
What are the 3 conditions called when the implantation occurs to deep?
Placenta accrete
Placenta increta
Placenta percreta
What are the 3 conditions called when the implantation occurs to deep?
Placenta accrete
Placenta increta
Placenta percreta
What is placenta accrete?
When the placenta invades beyond the functional layer (decidual) to basal layer
What is placenta increta?
When the conceptus invades through the myometrium
What is placenta percreta?
When the conceptus invades all the way through the entire uterus
How can you remember what depths are invaded too with the 3 to deep invasions?
Most superficial to deep in alphabetical order
Placenta acrete
Placenta increta
Placenta percreta
Why is invasion too deep bad?
Can cause significant post partum haemorrhage
What is pre eclampsia?
Condition where mother develops high blood pressure during pregnancy or post partum which can lead to proteinuria
Why does high blood pressure occur in pre-eclampsia?
Occurs since the conceptus doesn’t invade deep enough it is too shallow
This leads to blood vessels that develop being too narrow
This can lead to poor blood flow to placenta and therefore causing high blood pressure ini the mother
What is the general function of the placenta?
Supports the growing fetus
What are the main functions of the placenta?
Transfer:
-gas exchange
-nutrient exchange
-waste removal
-transferring IMMUNITY
Endocrine:
-protein hormones
-steroid hormones
The hormones maintain pregnancy
What are some protein hormones produced by the placenta?
Human chorionic gonadotrophin (HCG)
Human placental lactogen (hPL)
Placental growth hormone (PGH)
Corticotropin-releasing hormone (CRH)
What is thee function of HCG?
Maintains the corpus luteum which produces high amounts of progesterone (little oestrogen) maintains pregnancy
What are the steroid hormones made by the placenta?
Progesterone
Oestrogen
What cells produce HCG in the placenta?
Syncytiotrophoblasts
So is pregnancy specific
What is a disease where HCG is made?
Trophoblast disease called molar pregnancy
What is a molar pregnancy?
A non viable pregnancy where there’s the wrong number of chromosomes
Must be treated like a miscarriage
Why must a molar pregnancy be treated seriously as a miscarriage?
Molar pregnancies can become a malignancy called Choriocarinoma
What is the importance of the steroid hormones (progesterone and oestrogen made by the placenta?
Maintains the pregnancy state taking over from the corpus luteum
How are substances transported across the placenta?
Simple diffusion
Facilated diffusion (glucos)
Active transport
What cells express the transporters for active transport in the placenta ?
Syncytiotrophoblasts
What is actively transported across the placenta?
Amino acids
Iron
Vitamins
Why is good uteroplacental circulation essential for survival of the embryo?
Gas exchange relies on simple diffusion
So good blood flow needed to maintain a good concentration gradient
Why are women advised to lie on the side when they’re pregnant not on their back?
Baby will compress aorta reducing blood supply to placenta imparting conc grad for gas exchange
How is passive immunity granted to the developing embryo in the placenta?
IgG taken up by receptor mediated endocytosis
What blood vessels transport wastes like CO2, urea, uric acid and bilirubin from the baby to the placenta?
Umbilical arteries
What is a teratogen?
An agent that causes malformation in the embryo
What are some harmful substances that can cross the placenta?
Thalidomide
Alcohol (fetal alcohol syndrome)
Therapeutic drugs (anti epileptic drugs, warfarin, ACE inhibitor)
Drug abuse (fetus becomes dependant)
Maternal smoking (affects placental growth)
What is an example of an anti-epileptic drug?
Sodium valproate
What negative affect on development can sodium valproate have?
Neural tube defects
What are the 4 stages teratogenesis can occur?
Pre-embryonic (lethal effects)
Embryonic (very sensitive)
Fetal (quite sensitive)
After embryonic period ( risk for structural defects is low) except CNS
What are the main serious infections that can cross the placenta in pregnancy?
Toxoplasmosis
Other- syphilis, HIV, varicella
Rubella
Cytomegalovirus
Herpes Simplex
How can you remember the infections that can cross the placenta in pregancy?
TORCH infections
Toxoplasmosis
Other - syphilis, HIV, varicella
Rubella
Cytomegalovirus
Herpes simplex
Where do you risk picking u ptoxoplasmosis?
Around cats
