Maternal plasma but NOT maternal blood is found in the intervillous space whilst there is still the trophoblast plug
Premature blood flow and miscarriage?
In the missed miscarriage poplualtion there is an increase in maternal blood flow during the first trimester. This perfusion was also noted to be from the middle rather than from the outside inwards, this oxygen exposure may contribute to the miscarriage.
Villous - Branch of the placenta
Villous cytotrophoblast - trophoblast progenitor cell type found mainly in the first trimester underlying the STB
Syncytiotrophblast - Surface layer of the placenta formed by fusion of VCTB. STB does not replicate but is replaced by fusion of additional VCTB.
Extravillous cytotrophoblast - Differentiated cells that have migrated out of the villous placenta towards the maternal tissues.
Structural changes with gestational age in the placenta?
- During early pregnancy, stroma of the vili become more cellular and more vascularised
- during the 2nd trimester villous cytotrphoblast thins down
- during the 3rd trimester villous cytotrophoblast is sparse
- branching of villi increases
- size of the placenta increases
Maternal contributions to the placenta?
Decidua basalis - decidua underlying the implantation site
Desidua capsularis - decidua overlying the implantation site
Desidua peritalis -desidua around the remaineder of the uterus
As gestation progresses the amniotic cavity enlarges obliterating the uterine cavity. The decidua capsularis then fuses with the decidua peritalis
The placental membranes?
Amnion: Avascular membrane that covers the cord and the placenta (amniotic epithelium)
Chorion: Covers the fetal vessels (formed from trohphoblas that formed villi before regressing) .
Formation of the umbilical cord?
- From the yolk sac and the allantois
- The vessels of the cord are derived from the allantois
- 2 arteries and 1 vein
Whartons jelly consisting of a network of myofibroblasts with spaces filled by mucopolysaccharides (that keep the cord turgid)
All to increase transport the placenta:
- Has a tortuous structure with large SA
- The syncytiotrophoblast has microvilli
- In the third trimester mot villi are small tertiary villi
- In the third trimester the fetal capillaries are closely apposed to the syncytiotrophoblast (actually bulging the STB ito the maternal blood)
Gas transfer at the placenta?
Fetal blood has a greater affinity for oxygen due to Hbf
- At pO2 30torr hbf will be 80% saturated vs hb at 50%
Fetal blood has more haemaglobin and can thus carry more oxygen
- 20-25 ml/dl but adults are limited to 15.3ml/dl
The Bohr and Haldane effects?
The BOHR EFFECT
- As maternal blood picks up fetal metabolites the pH lowers. Thus, the affinity for oxygen decreases and dissociation of oxygen increases. The converse occurs on the fetal side.
The HALDANE EFFECT
- The capicty of Hb to bnd CO2 is related to the amount of bound oxygen. Thus, if oxygen is lost from the maternal blood its capacity to carry CO2 increases. Converse occurs on fetal side.
Amniotic fluid functions?
- Buoyant medium allows symmetrical growth (with even pressure so that on part of the fetus isn't being 'pushed' on.
- Cushions the embryo/fetus
- Prevents adhesions of the fetus with the membranes
- Allows the fetus to move - muscle development
- Development of GI/respiratory tracts - breathing and swallowing
Amniotic fluid production? How much do we have?
- Initially an ultra filtrate of maternal plasma
- Major fetal contribution later (urine)
- 20+ weeks fetal urine and some from surface of placenta + cord
By Term there is 800-1000mL
Human fetal urine output?
Humans put out about 500-1200mL/day which is extremly high for their size. It is recycled primarily by swallowing (500-1000mL) as well as across fetal skin. Lastly, some is throught the membranes into the mothers circulation.
Conditions relating to amniotic fluid?
- Excessive amniotic fluid possibly due to loss of swallowing
- Found in many cases of diabetic pregnancy
- not enough fluid potentially due to kidney problems
Amniocentesis and Chorionic villus sampling
Placenta acts as a barrier to/not to?
- Malaria - but the intervillous space becomes clogged with macrophages
- small pox
Useful drugs to give to mothers for fetus?
- Glucocorticoid given to prevent respiratory distress syndrome by increasing the speed of lung maturation.