✓ 28- Maternal-Fetal Exchange

Question 1

What metabolic changes are seen in the mother during the first phase of pregnancy?

Answer 1

Mother in anabolic state

• N/↑ sensitivity to insulin
• N/↓ levels of glucose, amino acids, free fatty acids and glycerol in plasma
• ↑ Lipogenesis
• ↓ Lipolysis
• ↑ glycogen stores in liver and muscle
• ↑ protein synthesis

Question 2

What metabolic changes are seen in the mother during the second phase of pregnancy?

Answer 2

Mother in catabolic state

• Shift to accelerated starvation due to accelerated rate of fetal and placental growth
• Insulin resistance
• ↑↑ postprandial levels of glucose and AA due to breakdown of dietary carbohydrates, protein and fat
• ↑↑ rate of glucose diffusion
• ↑↑ rate of facilitated amino acid transport across the placenta to the fetus
• Accelerated lipolysis
• ↑ FFA, Glycerol and Ketoacid levels in maternal plasma

Question 3

What metabolic changes during the second half of the pregnancy ensure alternative oxidative fuels for mother?

Answer 3

• Accelerated lipolysis
• ↑ FFA, Glycerol and Ketoacid levels in maternal plasma

Question 4

What can be used by the growing fetus as an alternative to glucose?

Answer 4

Ketoacids and FFA

Question 5

What is the function of the Placenta?

Answer 5

• Diffusion of foodstuffs from mother to fetus
• Diffusion of excretory products from fetus to mother

Question 6

Describe the total diffusion conductance of the placenta during the first few weeks of pregnacy

Answer 6

Modest at first due to:

1. Low permeability of the placenta due its small size and thick membranes
2. Small SA

Question 7

Describe the total diffusion conductance of the placenta during the later stages of pregnacy

Answer 7

Increases:

1. Thinning od membrane diffusion layers
2. Increased SA

Question 8

How is oxygen transported through placental layers?

Answer 8

By simpl diffusion, which is driven by the oxygen pressure gradient [20 mmHg]

Question 9

What is the mean maternal and fetal PO2 near the end of the pregnancy?

Answer 9

Maternal PO2 = 50 mmHg

Fetal PO2 = 30 mmHg

Mean pressure graadient is 20 mmHg

Question 10

What non-protein nitrogens are excreted?

Answer 10

• Urea
• Uric Acid
• Creatinine

Question 11

What is the mean maternal and fetal PCO2 near the end of the pregnancy?

Answer 11

Maternal PO2 = 37-38 mmHg

Fetal PO2 = 40 mmHg

Question 12

What is the effect of the low pressure gradient of PCO2 on its diffusion?

Answer 12

This extremely low pressure gradient is sufficient for the diffusion of CO2 from fetus to mother aided by the extreme solubility of CO2 in the placental membranes allowing it to diffuse 20x as rapidly as O2

Question 13

How does Glucose diffuse through the placenta?

Answer 13

Facilitated diffusion of glucose by carrier molecules in the trophoblast cells of the membrane

Question 14

Compare glucose levels in fetal and maternal blood

Answer 14

its level in fetal blood is 20-30% lower than that in maternal blood

Question 15

How does FFA diffuse through the placenta?

Answer 15

highly soluble, diffuse from maternal blood into fetal blood, but more slowly than glucose allowing glucose to be used more easily by the fetus for nutrition

Question 16

What ‘foodstuff’ difuses to the fetus?

Answer 16

• Glucose
• FFA
• Ketone bodies
• Potassium
• Sodium
• Chloride

Question 17

How does fetal tissue obtain sufficient O2 even though its PO₂ is 30 mmHg?

Answer 17

1. Fetal hemoglobin shifts oxygen dissociation curve to the left [carry 20-50% more haemoglobin than maternal hemoglobin]
2. Hemoglobin concentration of fetal blood is 50% greater than that of mother
3. Double bohr effect

Question 18

What is the double Bohr effect?

Answer 18

Bohr shift occurs in one direction in the maternal blood and in the other direction in the fetal blood

• Fetal blood entering the placenta carries large amounts of carbon dioxide, but much of it diffuses from the fetal blood to the maternal blood.
• Loss of the carbon dioxide makes the fetal blood more alkaline and the increased carbon dioxide in the maternal blood makes it more acidic.
• → increase in ability of the fetal blood to combine with oxygen while decreasing the ability in the maternal blood.
• → expels more oxygen from the maternal blood and enhances oxygen uptake by the fetal blood. The

Question 19

What does the Bohr effect state?

Answer 19

haemoglobin can carry more oxygen at a low PCO2 than it can at high PCO2