L17 Part 1 Placenta Flashcards
Fertilisation process
Sperm and ovum meet in fallopian tube 12-24 hours after ovulation
Fusion occurs and 2nd meiotic division occurs
Acrosome reaction makes ovum impermeable to other sperm
End - zygote - has diploid (46 chromosomes)
Zygote to blastomere
Zygote
2 cell stage
4 cell stage
8 cell stage
Morula (72 hours)
Blastocyst (4 days)
Days 4-5
Morula develops..? becomes .x.?
what happens to x?
rest of the cells.. creates..
blastocyst reaches .. ready for..
The morula develops a cavity and becomes known as a blastocyst
Blastocyst thins out and becomes the trophoblast - start of the placenta
The rest of the cells move (are pushed up) to form the inner cell mass. This creates an embryonic pole
The blastocyst has now reached the uterine lumen and is ready for implantation
Days 6-7 Bilaminar disc of the embryo
what forms epiblast + hypoblast?
2 layers are =
hypoblast forms (2)
epiblast forms
what develops within epiblast mass?
Inner cell mass: differentiates into two layers: epiblast and hypoblast
These two layers are in contact
Hypoblast forms extra embryonic membranes and the primary yolk sac
Epiblast forms embryo
Amniotic cavity develops within the epiblast mass
Days 16+
how does the bilaminar disc develop further? aka =
initiated by =
epiblast =
what happens to hypoblast ?
epiblast
Bilaminar disc develops further by forming 3 distance layers (this process is known as gastrulation)
Initiated but he primitive streak
The epiblast becomes known as ectoderm
The hypoblast is replaced by cells from the epiblast and becomes endoderm
The epiblast gives rise to the third layer, the mesoderm
Embryo - the 3 germ layers
The hypoblast degenerates
The epiblast gives rise to all 3 germ layers
The embryo folds to create the adult pattern
The development of the placenta
Syncytiotrophoblast burrows into the myometrium of the uterus - the syncytiotrophoblasts invading the maternal spiral arteries and starting the formation of the primary/secondary and tertiary villi
Formation of the placenta (5)
Synctiotrophoblast invades decidua (endometrium)
Cytotrophoblast cells erodes maternal spiral arteries and veins
Spaces (lacunae) between them fill up with maternal blood
Followed by mesoderm that develops into foetal vessels
Aiding the transfer of nutrients, O2, across a simple cellular barrier
Cytotrophoblast cells (CTB) (4)
Undifferentiated stem cells
Invade the maternal blood vessels and destroy the epithelium
Give rise to the syncytiotrophoblast cells (STB)
Reduce in number as pregnancy advances
Syncytiotrophoblast cells (STB) (3)
Fully differentiated cells
Direct contact with maternal blood
Produce placental hormones
The placenta as an endocrine organ (2)
Human chorionic gonadotrophin (HCG)
- maintenance of corpus luteum of pregnancy
- progesterone and oestrogen
Human placental lactogen HPL
- growth, lactation
- carbohydrate and lipid
Placental barrier (4)
Maternal blood in the lacunae in direct contact with syncytiotrophoblasts
Mono layer of syncytiotrophoblast/cytotrophoblast/foetal capillary epithelium is all that separated the foetal and maternal blood
Cytotrophoblasts decrease as the pregnancy advances (not needed)
The barrier thins as pregnancy advances leading to a greater surface area for exchange (one 10m^2)
Transfer across the placenta (5)
Gases - oxygen and carbon dioxide by simple diffusion
Water and electrolytes
Steroid hormones
Proteins poor - only by pinocytosis
Transfer of maternal antibodies IgG - starts at 12 weeks - mainly after 34 weeks therefore lack of protection for premature infants
Names parts of the decidua (3)
Capsularis - overlying embryo and chorionic cavity
Parietalis - side uterus not occupied by embryo
Basalis - between uterine wall and chorionic villae
Vasa praevia
Velomentous cord insertion that runs across the cervical os
Vasa praaevia: What can happen if the foetal vessels within the umbilical cord rupture? (4)
The foetal vessels within the umbilical cord pass over the internal os
As the internal os dilates in labour the vessels are stretched and exposed and can rupture leading to massive foetal blood loss and death
Diagnosed on ultrasound using colour dopplers
Management deliver by C section when the foetus is above 34 weeks
Clinical aspects of the placenta (3 in relation to where placenta is in uterus)
Position of the placenta within the uterus
- mainly fundal (at the top)
- anterior or posterior (front wall or back wall)
- low lying or placenta praevia (near to cervical os)
Placenta praaevia (4)
Massive bleeding in pregnancy
Painless bleeding
Foetal death
Maternal death
Failure of trophoblastic invasion into maternal circulation at 12 and 18 weeks (4)
Poor maternal foetal mixing of blood
Lack of oxygen and nutrients to the foetus
Leads to foetal growth restriction
Pre-eclampsia (raised BP)
Placenta Accrete (2)
The placenta has invaded too deep into the myometrium and thus after birth the placenta cannot separate and stays within the uterus
As a consequence the uterus cannot contact down and massive bleeding can occur leading to the requirement to do a hysterectomy
Placental abruption (4)
Massive bleeding in pregnancy (often concealed)
Extremely painful
Foetal death
Maternal death
How is placental abruption different to placenta praevia?
Bleeding can be concealed in placental abrasion i.e. not seen vie the vagina but the uterus fills up with blood
Different to placenta praevia where the blood is seen from he vagina
Placenta in multiple pregnancies
Can lead to conjoined twins - see slide (MCMA)
