5 - Placental Function Flashcards
What is the shape of the mature placenta?
Diameter - 15-20cm
Weight - 500g
Thickness - 2.5cm at centre
Where is the placenta usually situated?
upper uterine segment 99.5%
posterior surface 2/3
anterior surface 1/3
What is the difference between the fetal and maternal placenta surfaces?
Fetal: smooth, glistening & covered in amnion with the umbilical cord inserted in the centre with vessels radiating from it
Maternal: dull, greyish and divided into 15-20 cotyledons (lobes)
What do umbilical arteries do?
• Umbilical arteries take blood away from the baby and to the placenta
What do umbilical veins do?
Umbilical veins take blood from the placenta to the baby
What is the main circulation to a foetus?
- 2 umbilical arteries to the placenta
* Smaller branches to chorionic villi
Where does the main site of exchange occur in a foetus?
capillary networks in terminal branches of chorionic villi
• Vessels consolidate to form larger venous branches that join to form the umbilical vein which leaves the placenta
What is the maternal circulation?
- 80-100 spiral arteries open directly into the intervillous spaces
- Low blood pressure
- Villi bathed in maternal blood
- Return via venous pathways in decidual plate of placenta
Why is a placenta necessary?
Fetus requires nutrition
Luteal regression needs to be prevented
What is the function of the placenta?
- Gas exchange
- Nutrient exchange
- Waste exchange
- Synthesis of proteins and enzymes
What is the difference between foetal and adult haemoglobin?
o Foetal haemoglobin has more affinity and carrying capacity than adult haemoglobin
What does the rate of diffusion depend on?
Rate of diffusion depends on the gas gradient, blood flow, placental permeability and placental surface area
What nutrients are exchanged from fetus to mother?
CO2, water, urea, bilirubin, hormones, rbc antgens
What nutrients are exchanged from mother to fetus?
O2, Water, Hormones, Antibodies, Drugs, Carbohydrates, Amino Acids, Lipids, Toxic substances
How is glucose transported?
GLUT transporters
Which molecules are not allowed through?
- Heparin
- Insulin
Which foetal cells can cross the placenta?
o Granulocytes o Nucleated blood cells o Lymphocytes o Gametocytes o Trophoblast cells
What is the function of hcG synthesis?
maintains corpus luteum in early pregnancy
What does human placental lactogen do?
increases free fatty acids, promotes foetal growth, mammary duct proliferation
What does oestrogen and progesterone do?
maintains pregnancy after corpus luteum degnerates
What is the function of human placental growth hormone, insulin like growth factors?
o Human placental growth hormone – regulates maternal blood glucose levels
o Insulin like growth factors – stimulates proliferation and differentiation of the cytotrophoblast
What is the function of relaxin?
softens cervix and pelvic ligaments
Why is the foetus not rejected by the maternal immune system?
• HLA expression
o Trophoblasts express HLA G which is not recognised by the host immune system
• Infiltrating leukocytes secrete IL-2 which regulate the immune system
• Decidual reaction when the decidual cells become swollen and tightly compacted together which forms a carrier between the mother and implanting embryo
What are the pathologies associated with abnormal placental development?
Pre-eclampsia
Intrauterine growth restriction
Early miscarriage
What is placental completeness?
Retained placental tissue associated with postpartum haemorrhage and infection
What issues can occur with placental size?
o Less than 2.5cm thick are associated with intrauterine growth retardation
o More than 4cm thick associated with maternal diabetes, foetal hydrops and intrauterine foetal infections
What are the issues that can arise from placental consistency and surfaces?
o Maternal surface
Pallor shows foetal anaemia so could indicate haemorrhage
Clots on the surface can show placental abruption
o Foetal surface
Thick ring of membranes can show circumvallate placenta which is associated with prematurity, prenatal bleeding, abruption, mulitparity and early fluid loss
What are cord knots?
o If the foetus passes through a loop of the umbilical cord and then tension is placed on the cord during labour or delivery it can cut off blood flow to the baby
What are cord vessels?
o If only 1 foetal artery is present, the foetal anomaly rate is almost 50%
