Repro 9.1 fetal physiology.

Question 1

Where does materno-foetal exchange occur?

Answer 1

At the placenta, at the tips of the chorionic villi.

Question 2

What is the function of the umbillical vein?

Answer 2

To carry oxygenated blood from the placenta to the fetus

Question 3

What is the function of the umbillical artery?

Answer 3

To carry de-oxygenated blood from the fetus to the placenta

Question 4

How do the maternal and fetal pO2 levels differ?

Answer 4

The maternal pO2 is much greater than the fetal pO2.

The maternal pO2 increases marginally during pregnancy, but the fetus’ pO2 i much lower in general.

Question 5

What is the approximate pO2 of the fetus compared to maternal pO2?

Answer 5

maternal-11-13 kPa

fetal-around 4kPa.

Question 6

What factors increase fetal O2 content?

Answer 6

• fetal haemaglobin variant
• increased haematocrit
• higher concentration of haemaglobin.

Question 7

Give some features of fetal haemaglobin which help to increase O2 content of the fetus:

Answer 7

• Contains 2 alpha and 2 gamma subunits
• has a higher affinity for oxygen than adult haemaglobin
• doesn’t bind 2,3 DPG as effectively as adult haemaglobin, which normally leads to decreased O2 affinity, therefore affinity is not affected.

Question 8

Explain the double bohr effect seen during pregnancy:

Answer 8

• CO2 passes from the fetus to the mother.
• fetal blood becomes less acidic due to loss of CO2, this shifts the ODC to the left, promoting O2 uptake.
• maternal blood becomes more acidic due to increased CO2 content, leading to a shift of the ODC to the right, and promoting loss of O2.

(Basically on one side youre wanting to give O2 up, and on the other side you’re wanting to accept it.)

Question 9

How is the maternal CO2 level compared to the fetal CO2 level and how is this maintained?

Answer 9

Maternal pCO2 is lower than the fetal pCO2.

Progesterone dives hyperventilation, which increases exhalation of CO2, so maternal blood CO2 remains low.

Question 10

Describe the double Haldane effect:

Answer 10

As Hb gives up O2, it can accept CO2 more readily.

So as maternal Hb is giving up O2, it is accepting the CO2 from the fetus,

likewise as the fetus is giving up CO2, it can accept O2 from the mother.

There is no change in the local maternal concentration of CO2 because it is going from fetal blood to being bound to Hb.

Question 11

What shunts are seen in the fetus?

Answer 11

• Ductus venosus
• ductus arteriosus
• foreamen ovale

Question 12

What is the function of the ductus venosus?

Answer 12

Shunts blood from the umbilical vein to the IVC, bypassing the liver.

If this didn’t exist, the liver, which is very metabolic, would use a large amount of the O2 in the blood, so there wouldn’t be enough left for development of the fetus.

Question 13

What is the adult remenant of the ductus venosus?

Answer 13

ligamentum venosum, which runs within the ligamentu teres of the liver.

Question 14

What is the function of the foreamen ovale?

Answer 14

Conducts blood from the RA (which has high pressure) to the LA (lower pressure) to avoid most of the blood travelling to the lungs, which are delicate so would become damaged, and are non functioning.

Question 15

Why doesn’t the foreamen ovale persist once born?

Answer 15

Baby takes first breath, which increases the pressure in the left side of the heart, which pushes the leaves of the shunt closed.

Question 16

Does all the blood bypass the lungs?

Answer 16

No, a small amount of blood must travel through the RV, the pulmonary artery to the lungs, to aid their development.

Question 17

What are the functions of the LA during fetal life?

Answer 17

Accepts the blood which has shunted through the foreamen ovale.

Also gets a small amount of pulmonary venous return from the lungs, which is deoxygenated (no breathing occuring during gestation) which gets pumped to the LV and to the aorta.

Question 18

Which organs get the largest proportion of O2 in the fetus?

Which anatomical feature supports this?

Answer 18

• Brain, Heart.
• Ductus arteriosus joins the aorta after branches for the brain and heart have happened. Blood returning through the ductus arteriosus is deoxygenated, so by making branches to the heart and brain before this, the pO2 isn’t affected by the deoxygenated return.

Question 19

What is the function of the Ductus arteriosus?

Answer 19

Shunts blood from the pulmonary trunk and the right ventricle to the aorta.

This shunt happens after the branches supplying the head and heart are made, to reduce the effect of the addition of de-oxygenated blood.

Question 20

What is the fetal response to transient drops in pO2?

Answer 20

detected by th chemoreceptors

leads to stimulation of vagal activity
reduction in heart rate (to reduce O2 demands)

Also get redistribution of flow to prioritise the heart and brain, reducing blood flow to the GIT, kidneys and limbs)

Question 21

What are the effects of chronic hypoxaemia on the fetus?

Answer 21

Can lead to growth restrictions

behavioral changes such as reduced movement, impaired development.

Question 22

What hormones are necessary for fetal growth?

Answer 22

• insulin
• Insulin like growth factors:
• – IGF I-nutrient dependant, dominates in timesters 2, 3
• – IGF II- nutrient independant, dominates in trimester 1
• leptin

Question 23

What can be the effects of malnutrition on fetal growth?

Answer 23

• Can lead to symetrical or asymetrical growth restriction

- Can lead to changes for health in later life although not well understood, (epigenetics, barker hypothesis)

Question 24

What are the dominant cellular growth mechanisms in the different trimesters in pregnancy?

Answer 24

1st trimester- hyperplasia

2nd trimester- hyperplasia and hypertrophy

3rd trimester- hypertrophy

Question 25

What is the function of amniotic fluid?

Answer 25

Mainly protection for the fetus

-contributes to lung development

Question 26

What is the volume of amniotic fluid at:

8 weeks

38 weeks?

Answer 26

8 weeks- around 10ml

38 weeks- around 1 litre

Question 27

What happens to the volume of amniotic fluid after 38 weeks and why?

Answer 27

It’s volume depletes, the placenta has a built in time scale of 38 weeks, after which its function diminishes.

Question 28

How does amniotic fluid help with development of the lungs?

Answer 28

Whilst in the amniotic fluid, the fetus does some ‘practice breaths’ in which amniotic is inhaled into the lungs and aids the development.

Question 29

What is the composition of amniotic fluid?

Answer 29

98% water

electrolytes, creatinine, urea, glucose, bile pigments, lanugo, vernix caseosa

Question 30

What is the function of lanugo?

Answer 30

It’s a fine hair coverring which covers the fetus.

Question 31

What is the function of vernix caseosa?

Answer 31

Waterproofs the fetus’ skin to help protect it.

Question 32

How is amniotic fluid produced and recycled?

Answer 32

produced through the kidneys and urination,

recylced via lung movements, swallowing, and the placental and fetal membranes.

Question 33

What is meconium?

Answer 33

‘baby poo’

The debris of the amniotic fluid as it passes through the GI tract. Shouldnt be released until after birth.

Question 34

What are some complications of meconium being passed before birth?

Answer 34

• due to practice breathing it can lead to respiratory distress
• the presence of the meconium into the amniotic fluid can cause distress of the child.
• the amniotic fluid will become tinged yellow/green.

Question 35

What is amniocentesis?

Answer 35

Sampling of the amniotic fluid using a probe that is ultrasound guided.

allows collection of fetal cells which can be used for genetic testing.

Safer than chorionic villus sampling which carries a higher mortality rate.

Question 36

How is billirubin metabolism conducted in the fetus and why?

Answer 36

via the placenta,

The fetus has no way of excreting billirubin, so it doesnt conjugate it which allows it to be transfered to the placenta and to the mothers circulation.

Question 37

Why is physiological jaundice common in the fetus?

Answer 37

The fetus has to quickly change to conjugating it’s own billirubin after birth, something which it hasn’t had to do before.

it commonly just resolves itself.