Lecture 11 & 12 - Placenta Flashcards
Development of placenta from time of implantation?
- Blastocyte is free floating in uterine cavity
- Blastocyst fuses with the uterine lining it forms the primitive sensillium
- The inner cells are called cytotrophoplasts and outer layer is syncytiotrophoblast layer
- Secretes enzymes which digest maternal uterine cells and embreyo starts to get into uterus
- Fluid filled gaps form called lacunae form in dicidua, where bits of sensilium will go into - these are called trabeculae
- the trophectoderm is now called trophoblast protrusions (trabeculae) which go into the lacunae
- cytotrophoblasts priliferate and invade the trabechulae to become primary villi (placental villi)
- lacunae now called intervillous space
- extraembyonic mesenchyme invade the primary villi forming secondary villi
- then become tertiary villi
- when see umbilical vessels in there - then this is a tertiary villus
Floating villi - do not have contact with maternal tissues but are in intervillous space and are responsible for exchange and barrier functions of the placenta
Anchoring villi - a few villi cytotrophoblasts break through the synctiotrophoblast, and form a cytotrophoblast shell
-this remains in contact with amternal tissue throguh gestation
Anchoring Villi
a few villi cytotrophoblasts break through the syncytiotrophblast, and spread laterally around the implantation site to form a cytotrophoblast shell
- this shell ramins in contact with the maternal tissue throughout gestation
- columns of cytotrophoblast continue to stream out of these anchorign villi to invade the decidua and spiral arteries durign first and second trimesters
What happens to spiral arteries during placenta formation?
What happens if dont have this?
Extravillous trophoblasts invade down into the spiral arteries
- remove epithelial cells and smooth muscle
- no tonic response in spiral arteries
- the arteries are big, and do not respond to tonal stimuli - does not reduce blood flow to placenta in fight or flight mode
- need good perfusion of placenta always (dont want lack of oxygen to fetus- brain damage)
If dont have these vessels lined by extravillious trophoblasts then get less perfusion to the placenta - Small gestational age baby
-likely to be born prematurely and stillborn (has not reached its growth potential)
Plugged spiral arteries
Endovascular trophoblast plugs - doesnt allow red blood flows from spiral artery blood to flow into placenta (allows plasma to flow through)
- also stops pulsatile flow
- increased maternal blood flow - can cause placental damage - can cause a miscarriage
- can get a mis-miscairage where the women is presenting with signs that she may have a miscariage but condition resolves
- when looked a blood flow - increased blood flow to the placenta to central placenta
-restriction of the blood flow can help damage to the placenta
Glandular milk?
Up to 12 weeks -
Glandular milk moves out through the placental villi into the intervillous space
-fetus not relying on maternal blood
-Uterine glands - supply fetus with nutreients in first few weeks of life
Definitions
Villous
Villous cytotrophoblast
Villous - branch of placenta
Villous cytotrophoblast - trophoblast progenitor cell type found mainly in the first trimester underlying the STB
Syncytiotrophoblast - surface layer of placenta formed by fusion of VCTB.
Extravillous cytotrophoblast - differentiated cells that have migrated out of the villous placenta towards maternal tissues
Why do we care about the placenta early on?
even before implantation can get infertility, can prevent this if know what is going on
- Structural changes with gestational age
- during early pregnancy stroma of the villi become more cellular and more vascularised
- 2nd trimester - villour cytotrophoblast thins down (for more exchange)
- 3rd trimester - villous cytotrophoblast is sparse
- branching of vili increases (much more dense with mesncinal cells)
- size of placenta increases
What happens during menstrual cycle to prepare for pregnancy?
- Endometrium undergoes changes during the cycle - called decidual reaction
- the stromal cells of dicidua are swollen and store glycogen - for energy for feotus
- upon implantation the reaction is enhanced.
Why are all the arteries in uterine wall coiled?
Uterus needs to expand to accomodate size of baby, reason vessels are coiled is so they dont have to grow when the baby is growing - dont have to waste as much energy
-may also slow down blood flow - force in which it hits the placenta
- Placental membranes
-amnion - avascualr and covers the cord and placenta
Chorion - fetal vessels
Decidua - derived from decidua capsularis and peritalis - not a fetal membrane (from mother)
How is the umbilical cord made?
Formed from yolk sac and allantois
- 2 arteries and one vien
- has whartons jelly in it (protects cord for colapsing
- myofibroblsats
- mucoplysaccharides
What adaptations doe the placenta have?
- Large surface area of villous structure
- Syncytiotrophoblast - has microvillous surface - increase surface area for trasnport
- thirs trimester - most villi are small tertiary villi
- third trimester - fetal capillaries are clostly apposted to syncytiotrophoblast
Gas Transfer
Fetal blood - has greater affinity for oxygen than maternal blood due to Hbf
- fetal blood - has more haemoglobin, can carry more oxygen
- Bohr effect - maternal blood picks up fetal metabolites, these lower the pH on maternal side and will enhance release of oxygen
- opposite thing occurs on fetal side - increase oxygen affinity , metbolights released
- Double bohr effect
Haldane effect - (capactiy for Hb to bind to CO2 ) - is related to amount ofbound oxygen
-oxygen lost from maternal blood, increases the capacity for CO2 for maternal blood (form fetus)
Function Amniotic fluid
- buoyant - allows symmetric growth
- cushions the embryo/fetus
- Prevents adhesion of fetus with membranes
- allows fetus to move
- develop GI/ resp tracts - breathign and swallowing
