Foetal Physiology

Question 1

What type of blood is carried in the umbilical vein?

Answer 1

Oxygenated blood

Question 2

What type of blood is carried in the umbilical arteries?

Answer 2

Deoxygenated blood

Question 3

How does gas exchange take place at the placenta?

Answer 3

Thin diffusion distance

Down gradient of partial pressures

So foetal pO2 needs to be lower than maternal pO2

Question 4

What is the normal pO2 of foetal blood?

Answer 4

4kPa

Question 5

What factors promote O2 exchange at the placenta?

Answer 5

Increased maternal production of 2,3 DPG
Foetal haemoglobin
Double Bohr effect

Question 6

What makes up foetal haemoglobin?

Answer 6

2 α subunits + 2 γ subunits

Question 7

Why does foetal haemoglobin have greater affinity for oxygen?

Answer 7

Doesn’t binf to 2,3-DPG as effectively as adult Hb

Question 8

What is the double bohr effect?

Answer 8

Bohr effect on both mother’s haemoglobin and foetal haemoglobin

Question 9

What happens to the mother with the double bohr effect?

Answer 9

CO2 passes into intervillous blood
pH decreases
Bohr effect
Decreases affinity of Hb for O2

Question 10

What happens to the foetus with the double Bohr effect?

Answer 10

CO2 is lost
pH rises
Bohr effect
Increases affinity of Hb for O2

Question 11

How is CO2 transferred?

Answer 11

Double Haldane effect

Progesterone driven hyperventilation = lower maternal pCO2
- down concentration gradient

Question 12

What is the double Haldane effect?

Answer 12

As Hb gives up O2, it can accept more CO2
Foetus gives up CO2 as O2 is accepted
No changes in local CO2

Question 13

What are the foetal circulation shunts?

Answer 13

Ductus venosus
Ductus arteriosus
Foramen ovale

Question 14

What is ductus venosus?

Answer 14

Connects umbilical vein to IVC

• blood enters directly into RA
• shunts blood around liver
• maintains saturation

Question 15

What is ductus arteriosus?

Answer 15

Shunt from RV to aorta

• joins aorta distal to supply of head
• minimises drop in O2 sats

Question 16

What is foramen ovale?

Answer 16

Hole between RA + LA

• pressure in RA > pressure in LA
• blood flows into left atrium
• heart + brain get good supply of oxygen

Question 17

Which shunts bypass the lungs?

Answer 17

Foramen ovale

Ductus arteriosus

Question 18

What is the foetal response to hypoxia?

Answer 18

Redistribution of flow to supply heart and brain

Heart rate decreases to reduce O2 demand

Question 19

What are the effects of chronic hypoxaemia?

Answer 19

Growth restriction

Behavioural changes

Question 20

What hormones are necessary for foetal growth?

Answer 20

Insulin
IGF
Leptin

Question 21

What is symmetrical growth restriction?

Answer 21

Small head + small body

Question 22

What is asymmetrical growth restriction?

Answer 22

Normal head + small body

Question 23

What is the dominant cellular growth mechanism in weeks 0-20?

Answer 23

Hyperplasia

Question 24

What is the dominant cellular growth mechanism in weeks 20-28?

Answer 24

Hyperplasia + hypertrophy

Question 25

What is the dominant cellular growth mechanism in weeks 28- term?

Answer 25

Hypertrophy

Question 26

What is amniotic fluid?

Answer 26

FLuid that makes up amniotic sac

Question 27

What is the role of amniotic fluid?

Answer 27

Protection | Contributes to lung development

Question 28

What is volume of amniotic fluid at 8 weeks?

Answer 28

10ml

Question 29

What is the volume of amniotic fluid at 38 weeks?

Answer 29

1L

Question 30

What is the composition of amniotic fluid?

Answer 30

``` 98% water Electrolytes Creatinine Urea Renin Foetal cells ```

Question 31

What happens to amniotic fluid during pregnancy?

Answer 31

Foetus swallows fluid to absorb water + electrolytes | Most is excreted as urine

Question 32

What makes up meconium?

Answer 32

Debris from amniotic fluid + intestinal secretions

Question 33

What is amniocentesis?

Answer 33

Sampling of amniotic fluid

Question 34

What is oligohydramnios?

Answer 34

Lack of amniotic fluid production

Question 35

What can cause oligohydramnios?

Answer 35

Foetal kidney malfunction Premature membrane rupture Placental insufficiency

Question 36

What is polyhydramnios?

Answer 36

Increased amniotic fluid production

Question 37

What can cause polyhydramnios?

Answer 37

Excessive urine production Gestational diabetes Maternal hypertension

Question 38

How is bilirubin metabolised in the foetus?

Answer 38

Clearance of bilirubin handled by placenta | Foetus cannot conjugate bilirubin