5 - Placental Function

Question 1

What is the shape of the mature placenta?

Answer 1

Diameter - 15-20cm
Weight - 500g
Thickness - 2.5cm at centre

Question 2

Where is the placenta usually situated?

Answer 2

upper uterine segment 99.5%
posterior surface 2/3
anterior surface 1/3

Question 3

What is the difference between the fetal and maternal placenta surfaces?

Answer 3

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)

Question 4

What do umbilical arteries do?

Answer 4

• Umbilical arteries take blood away from the baby and to the placenta

Question 5

What do umbilical veins do?

Answer 5

Umbilical veins take blood from the placenta to the baby

Question 6

What is the main circulation to a foetus?

Answer 6

• 2 umbilical arteries to the placenta

* Smaller branches to chorionic villi

Question 7

Where does the main site of exchange occur in a foetus?

Answer 7

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

Question 8

What is the maternal circulation?

Answer 8

• 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

Question 9

Why is a placenta necessary?

Answer 9

Fetus requires nutrition

Luteal regression needs to be prevented

Question 10

What is the function of the placenta?

Answer 10

• Gas exchange
• Nutrient exchange
• Waste exchange
• Synthesis of proteins and enzymes

Question 11

What is the difference between foetal and adult haemoglobin?

Answer 11

o Foetal haemoglobin has more affinity and carrying capacity than adult haemoglobin

Question 12

What does the rate of diffusion depend on?

Answer 12

Rate of diffusion depends on the gas gradient, blood flow, placental permeability and placental surface area

Question 13

What nutrients are exchanged from fetus to mother?

Answer 13

CO2, water, urea, bilirubin, hormones, rbc antgens

Question 14

What nutrients are exchanged from mother to fetus?

Answer 14

O2, Water, Hormones, Antibodies, Drugs, Carbohydrates, Amino Acids, Lipids, Toxic substances

Question 15

How is glucose transported?

Answer 15

GLUT transporters

Question 16

Which molecules are not allowed through?

Answer 16

• Heparin

- Insulin

Question 17

Which foetal cells can cross the placenta?

Answer 17

o	Granulocytes
o	Nucleated blood cells 
o	Lymphocytes 
o	Gametocytes 
o	Trophoblast cells

Question 18

What is the function of hcG synthesis?

Answer 18

maintains corpus luteum in early pregnancy

Question 19

What does human placental lactogen do?

Answer 19

increases free fatty acids, promotes foetal growth, mammary duct proliferation

Question 20

What does oestrogen and progesterone do?

Answer 20

maintains pregnancy after corpus luteum degnerates

Question 21

What is the function of human placental growth hormone, insulin like growth factors?

Answer 21

o Human placental growth hormone – regulates maternal blood glucose levels
o Insulin like growth factors – stimulates proliferation and differentiation of the cytotrophoblast

Question 22

What is the function of relaxin?

Answer 22

softens cervix and pelvic ligaments

Question 23

Why is the foetus not rejected by the maternal immune system?

Answer 23

• 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

Question 24

What are the pathologies associated with abnormal placental development?

Answer 24

Pre-eclampsia

Intrauterine growth restriction

Early miscarriage

Question 25

What is placental completeness?

Answer 25

Retained placental tissue associated with postpartum haemorrhage and infection

Question 26

What issues can occur with placental size?

Answer 26

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

Question 27

What are the issues that can arise from placental consistency and surfaces?

Answer 27

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

Question 28

What are cord knots?

Answer 28

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

Question 29

What are cord vessels?

Answer 29

o If only 1 foetal artery is present, the foetal anomaly rate is almost 50%