Foetal Physiology

Question 1

What factors aid gas exchange between the foetus and the mother

Answer 1

Small diffusion barrier

Large surface area due to chorionic villi

Gradient of partial pressures is maintained

Question 2

What factors promote O2 exchange from the placenta to the foetus

Answer 2

Increased maternal production of 2,3-BPG

Foetal Hb - different varient and there is more foetal haematocrit thant in adult

Double bohr effect - foetus releases CO2 -> can pick up O2 more easily while mother’s Hb picks up CO2 -> releases O2 more easily

Question 3

How is foetal Hb specialised for the low pO2 of foetal blood

Answer 3

Foetal Hb has a higher affinity for O2 as it does not bind 2,3-BPG as effectively as adult Hb -> can bind O2 better

Question 4

How is CO2 transfer between foetus and mother maximised

Answer 4

Progesterone produced by the mother drives hyperventilation which decrease pCO2 in maternal blood creating a larger concentration gradient

There is a double haldane effect - maternal blood gives up O2 -> can accept increased amounts of CO2 while foetus gives up CO2 as O2 is accepted -> no alterations in local pCO2

Question 5

What is the foetal response to hypoxia

Answer 5

Transient decrease in oxygenation results in redistribution of blood flow to supply the brain and heart

Foetal HR slows in response to hypoxia to decrease O2 demand - vagal stimulation leads to bradycardia

By dropping demand foetus can survive until transient decrease in pO2 has been removed

Question 6

How does the growth of the foetus change during gestation

Answer 6

0-20wks - mainly hyperplasia

20-28wks - hyperplasia and hypertrophy

28wks to term - hypertrophy

Question 7

What are the types of growth restriction and how are they caused

Answer 7

Symmetrical - affects every part of foetal body. Occurs if malnutrition/hypoxia affects baby before 28wks/T3

Asymmetrical - head sparing growth restriction. Due to maternal hypoxia and/or nutritional deficiencies. Occurs after 28wks/T3. Brain shunts blood to itself -> have growth restriction elsewhere

Question 8

What hormones are nessessary for foetal growth

Answer 8

Insulin

IGFs

Leptin

EGF

TGF-alpha

Question 9

What are the functions of the amniotic fluid

Answer 9

Provides protection

Contributes to normal lung and GI development

Facilitates exchange of nutrients between foetus and mother

Question 10

Where is amniotic fluid produced from

Answer 10

Majority of amniotic fluid is produced by the urinary tract

Also produced by lungs, GI tract, placenta and foetal membranes

Question 11

What forms amniotic fluid

Answer 11

Water

Electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones, foetal cells, vernix caseosa

Question 12

What is meconium

Answer 12

Debris from amniotic fluid plus intesinal secretions including bile

Passes as first bowel movement

Question 13

What method can be used to sample amniotic fluid and why is amniotic fluid tested

Answer 13

Amniocentesis is used to sample amniotic fluid

Sampling is used to test foetal cells for genetic abnormalities

Question 14

When are the parts of the respiratory system formed

Answer 14

Bronchopulmonary tree form during embryonic period

Alveoli and sacs of respiratory system develop during foetal period

Question 15

Describe the development of the respiratory system

Answer 15

Wks 8-15 - pseudoglandular stage. Bronchopulmonary tree is formed -> lots of ducts and branches are formed

Wks 16-26 - canalicular stage. Formation of respiratory bronchioles

Wks 26 to term - terminal sac stage. 26th week is last possible week where alveoli form. Have differentiation of pneumocytes and production of surfactant

Question 16

Why does the respiratory system need to be conditioned and how does this occur

Answer 16

Respiratory system needs to be conditioned in order for lungs to be able to take over gas exchange after birth

Foetus does breathing movements to condition respiratory musculature

Question 17

What is threshold of viability

Answer 17

Threshold of viability - point at which viability of the foetus outside the uterus is possible

Question 18

What causes olgiohydramnios

Answer 18

Placental insufficiency

Renal impairment

Compromise of uteroplacental circulation

Question 19

What causes polyhydramnios

Answer 19

Assocaited with foetal abnormality like inability to swallow

Question 20

What neuronal tracts begin to form in the 4th month and what is their function

Answer 20

Corticospinal tracts

Required for coordinated voluntary movements

Question 21

When does myelination of the brain occur

Answer 21

Begins in 9th month and continues until after birth