Repro: Fetal physiology

Question 1

How does the umbilical circulation connect with the fetal circulation?

Answer 1

They don’t ever mix

There is diffusion - the barrier decreases thickness as pregnancy proceeds

Question 2

Fetal blood has a low pO2 compared to adults, what factors increased overall O2 content?

Answer 2

• fetal Hb different to normal Hb

- fetal haematocrit is higher

Question 3

What is the double bohr effect promoting O2 exchange?

Answer 3

There are 2 circulations running in parallel
As CO2 passes into the intervillus blood the pH decreases (bohr effect) decreasing affinity of Hb for O2

At the same time CO2 is lost so pH rises (bohr effect) increasing affinity of Hb for O2

Question 4

How does the mother cope with increased production of metabolic CO2?

Answer 4

Progesterone acts on the brain stem to cause physiological hyperventilation causing a reduction in maternal pCO2 so that there is conc gradient so fetal CO2 can transport into maternal blood

Question 5

What are the fetal circulatory shunts? What is the remnant in the adult?

Answer 5

Foramen ovale - bypasses the right ventricle to prevent blood going to the lungs. RA –> LA (remnant is the fossa ovalis)

Ductus arteriosus from pulmonary trunk to aorta to bypass lungs. Remnant is the ligamentum arteriosum

Ductus venosus goes from placenta to IVC to bypass the liver. Remnant is the ligamentum venosum

Question 6

How does the fetus respond to hypoxia because it cants change ventilation?

Answer 6

• increased HbF
• redistributes blood to the heart and brain
• bradycardia to reduce O2 demand (vagal stimulation causes bradycardia which is opposite in adults)
• eventually less movement and less REM sleep

Question 7

What hormones are needed for fetal growth?

Answer 7

• insulin to promote utilisation of nutrients
• IGF 1 and 2 (insulin-like growth factor)
  - IGF2 is nutrient independent and dominant in T1
  - IGF1 is nutrient dependent and dominant in T2+3
• leptin

Question 8

What are the dominant cellular growth mechanism throughout pregnancy?

Answer 8

0-20 weeks hyperplasia
20-28 weeks hyperplasia and hypertrophy
28 weeks-term hypertrophy

Question 9

What are the general functions of the amniotic fluid?

Answer 9

• protection
• critical for development of the lungs (practicing breathing movements)
• lubricant for movement
• practicing swallowing
• temperature regulation

Question 10

How does the volume of amniotic fluid change throughout pregnancy?

Answer 10

10ml at 8 weeks, increasing to 1 litre at term.
Post-EDD the volume reduces, the placenta is only designed to last the gestational period so start to see a decrease in function

Question 11

What is the composition of amniotic fluid?

Answer 11

98% water with electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones, fetal cells, lanugo (downy hair) and vernix caseosa

Question 12

How can you tell if meconium has been passed before delivery?

Answer 12

The amniotic fluid will be green (bile makes it green)

Its a sign of fetal distress, if any is swallowed it can cause respiratory distress

Question 13

What are the 2 methods of antenatal diagnostic tests?

Answer 13

Amniocentesis -less invasive but still a risk of miscarriage
Chorionic villus sampling - more invasive, take some chorionic villus cells from the placenta

Question 14

Why is jaundice so common in newborns?

Answer 14

Fetus cannot conjugate bilirubin due to immaturity of liver, therefore it is handled by the placenta
The jaundice is physiological