Lecture 15 - Fetal Physiology

Question 1

Adaptation of low foetal pO2

Answer 1

HbF
Foetal haematocrit is higher
More Hb
More bloody supply to brain and heart

Question 2

Foetal haemoglobin

Answer 2

Week 12 to term

2 alpha subunits and 2 gamma sub units

Greater affinity for oxygen because it doesn’t bind to 2,3 - DPG as effectively has HbA

Question 3

Factors promoting oxygen exchange

Answer 3

Increased maternal 2,3 diphosphoglycerate - secondary to respiratory alkalosis

At higher partial pressures it unloads more

Question 4

Double Bohr effect

Answer 4

1. As CO2 passes into the intervillous blood pH decreases
2. Affinity of oxygen decreases in maternal Hb (shift right)
3. CO2 lost in foetus therefore pH rises
4. Increases affinity for oxygen in Hb of foetus (shift left)

Question 5

Why is pCO2 lower in maternal blood

Answer 5

Progesterone driven hyperventilation

Maintains concentration gradient so foetal CO2 is transferred to mother

Question 6

Double Haldane effect

Answer 6

1. Maternal Hb gives up oxygen and accepts more CO2

2. Total blood loads more oxygen and gives up more CO2

Question 7

Foetal circulation

Answer 7

1. Receives oxygenated blood from the umbilical vein.
2. Bypasses the liver by the ductus venosus to the right atrium via the inferior vena cava
3. Right atrium to the left atrium via the foramen ovale as bypasses the lungs
4. From the aorta to the body to the umbilical artery to the maternal circulation
5. Some blood enters the right ventricle and pulmonary trunk which enters the aorta via the ductus arteriosus

Question 8

Ductus venosus

Answer 8

Umbilical vein to IVC

Bypasses liver as has a higher metabolic demand

Therefore maintains oxygen saturation

Question 9

Foramen ovale

Answer 9

Right atrial pressure is greater than the left atrial pressure in the foetus

For aces foramen ovale leaves apart and blood flows into the left atrium

Question 10

Crista dividens

Answer 10

Free border of septum secundum forms a crest

Minor proportion of blood flows into the right ventricle mixed with deoxygenated blood from the SVC

From the right ventricle it goes to the lungs to prevent right ventricular atrophy and supports lung development

Question 11

Left atrium

Answer 11

Small amount of pulmonary venous return (deoxygenated)

60% saturation as mixed with right atrial oxygenated blood

Pumped to LV and aorta

Question 12

Ductus arteriosus

Answer 12

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

Joins the aorta distal to the supply to the brain and heart to minimise drop in O2

Question 13

Foetal response to hypoxia

Answer 13

Foetal heart rate decreases - reduce oxygen demand

Increased haemoglobin

Redistribution of flow to protect heart and brain

Question 14

Foetal bradycardia

Answer 14

1. Chemoreceptors detect hypoxia

2. Vagal stimulation leading to bradycardia

Question 15

chronic hypoxia

Answer 15

Due to smoking

Effects:
Growth restriction
Behavioural change

Question 16

IGF I

Answer 16

Insulin like growth factor nutrient dependent

Dominant in 2nd and 3rd trimester

Question 17

IGF II

Answer 17

Nutrient independent

Dominant in 1st trimester

Question 18

Cellular growth mechanisms in each trimester

Answer 18

Trimester 1 - hyperplasia

Trimester 2 (20 -28 weeks) - hyperplasia and hypertrophy

Trimester 3 - hypertrophy

Question 19

Amniotic fluid

Answer 19

Amniotic sac encloses embryo and is filled with amniotic fluid

Provides mechanical protection and contains substances critical for lung development and surfactant production

Amniotic fluid is inhaled in the foetus to the foetal lungs

Swallowed - GI absorbs water and electrolytes and debris accumulates in the gut to form meconium

Question 20

Production and recycling of amniotic fluid

Answer 20

In early pregnancy amniotic fluid is produced by the placental and foetal membranes - intermembranous pathway

Foetal urine production - 9 weeks - amniotic fluid

Also produced by the lungs and GI tract a little

Question 21

Composition of amniotic fluid

Answer 21

98% water

Contains electrolytes + lanugo (fine hair) and vernix caseosa (white waxy substance that protects the skin)

Question 22

Meconium

Answer 22

Debris from foetus and instestinal secretions including bile

Passed after delivery of baby - green due to bile

Question 23

Amniocentesis

Answer 23

Sampling of amniotic fluid - collection of foetal cells

Used in foetal karyotyping and diagnostic test

Risk of miscarriage

Question 24

Bilirubin metabolism

Answer 24

Placenta clears foetal bilirubin during gestation

Foetus cannot conjugate bilirubin due to immature liver

Physiological jaundice - delay in new borns ability to conjugate and excrete bilirubin