Session 9: Fetal Physiology

Question 1

Progesterones effect on ventilation in pregnancy.

Answer 1

Causes hyperventilation leading to the mother developing a physiological respiratory alkalosis.

Question 2

Respiratory alkalosis in the mother would lead to increased pH and also increased maternal affinity for O2.

This is not favourable for giving up to the foetus. How is this resolved?

Answer 2

There is an increase in production of maternal 2,3-BPG to shift the dissociation curve back to the right to promote release of oxygen to the foetus.

Question 3

Why is progesterone-driven hyperventilation then important for giving up oxygen to the foetus?

Answer 3

It leads to a lower conc. of CO2 in the maternal blood. This means that the gradient allows gas exchange of CO2 from foetus to mother and ultimately lowers CO2 conc. in the foetus. This makes haemoglobin giving up CO2 and having higher affinity for O2.

Question 4

What is the haemoglobin in the foetus?

Answer 4

HbF 2 alpha and 2 gamma

Question 5

Why is HbF in foetal circulation?

Answer 5

Has greater oxygen affinity because it does not bind 2,3-BPG as maternal Hb does.

Question 6

Explain the double Bohr effect.

Answer 6

1 - As CO2 passes into intervillous blood the pH will decrease. This is in the maternal circulation leading to a decreased affinity for O2 in the mother.

2 - The foetus will give up CO2 leading to an increased pH in the foetus resulting in increased affinity for O2.

Question 7

What is the Haldane effect?

Answer 7

Maternal Hb gives up O2 promoting binding to CO2.

Foetal Hb gives up CO2 promoting binding to O2.

Question 8

What’s a possible foetal response to hypoxia?

Answer 8

Bradycardia via vagal stimulation.

This is done to reduced the O2 demand on the heart.

Question 9

What is harmful about bradycardia in the foetus?

Answer 9

A part of fetal distress and can lead to intrauterine growth restriction.

Question 10

Give a common cause of chronic hypoxaemia in foetus.

Answer 10

Smoking which can lead to intrauterine growth restriction.

Question 11

Shunts in foetal circulation.

Answer 11

Ductus venosus (to bypass the liver)

Foramen ovale (to bypass the lungs and straight into LA)

Ductus arteriosus (to bypass the lung but still get some blood into the RV and then into aorta instead of lungs)

Question 12

What hormones are key to foetal growth?

Answer 12

Insulin-like growth factors IGF-1 and IGF-2.

Question 13

What type of growth happens to cells in the first trimester?

Answer 13

Hyperplasia

Question 14

What type of growth happens to cells in the second trimester?

Answer 14

Hyperplasia and hypertrophy

Question 15

What type of growth happens to cells in the third trimester?

Answer 15

Mainly hypertrophy

Question 16

What type of growth restriction can maternal malnutrition cause?

Answer 16

Symmetrical growth restriction.

Asymmetrical growth restriction.

Question 17

What is symmetrical growth restriction?

Answer 17

All parts of the fetus are small

Question 18

What is asymmetrical growth restriction?

Answer 18

Called head sparing with growth restriction on the abdomen that will be smaller than head.

Question 19

Purpose of the amniotic fluid?

Answer 19

Mechanical protection and also contains substances that are critical for lung development.

Question 20

How does the volume of the amniotic fluid relate to the size of the foetus?

Answer 20

The volume is proportional to the size of the fetus.

Question 21

How is amniotic fluid clinically relevant in utero?

Answer 21

It contains foetal cells so amniocentesis can be done which where you aspirate amniotic fluid for analysis.

Question 22

Explain amniocentesis and its clinical relevance.

Answer 22

Aspiration of amniotic fluid.

This is important in foetal karyotyping for e.g. a definitive diagnosis for Down’s syndrome.

It is however invasive and carries a risk of miscarriage.

Question 23

Give a clinical sign of fetal distress related to meconium.

Answer 23

Meconium staining

Question 24

Explain what meconium staining is.

Answer 24

When meconium is prematurely released from the GI tract.

This can cause the fetus to inhale the meconium that has been released into the amniotic fluids.

This can lead to meconium aspiration

Question 25

When does amniotic fluid production start?

Answer 25

At around 9 weeks.

(It is basically a production of urine)

Question 26

Give two ways of how recycling of amniotic fluid is done.

Answer 26

Inhalation of amniotic fluid by the foetus to practice for breathing. This is also important for the production of surfactant.

Swallowing amniotic fluid so it enters the GI-tract of the foetus. Debris from the GI tract accumulate as the meconium.

Question 27

Composition of amniotic fluid.

Answer 27

Water

Electrolytes

Common substances from urine

Foetal skin

Question 28

Explain why there might be jaundice of a newborn.

Answer 28

There is sometimes a delay in a newborn’s ability to conjugate and excrete bilirubin.

However if this jaundice appears within 24 hours of partum then it can be indicative of a more serious pathology.

Question 29

State more examples of hormones necessary for foetal growth.

Answer 29

IGF-I

IGF-II

Insulin

Leptin (placental prod)

EGF

TGFalpha

Question 30

How is bilirubin metabolise in utero?

Answer 30

By the placenta as the fetus can’t conjugate bilirubin.

Question 31

What is the crista dividens?

Answer 31

A crest found on the free border of septum secundum.

This leads the formation of two streams of blood flow. One that goes to LA (majority) and then a minor proportion going to the RV.

Question 32

Fetal response to hypoxia

Answer 32

Increasing conc. of HbF

Redistribution of flow to heart and brain

Bradycardia to reduce O2 demand via vagal stimulation. (compared to in adults where tachycardia would ensue).

Growth restriction

Behavioural changes