Fetal Physiology Flashcards
What factors increase the fetal O2 content?
Fetal haemoglobin variant with increased affinity for oxygen,
Fetal haemocrit is increased over the adults.
What factors promote oxygen exchange to the fetus?
Increased maternal 2,3 BPG.
Fetal haemoglobin,
Double Bohr effect.
Why does fetal haemoglobin have a greater affinity for oxygen?
It doesn’t bind 2,3 BPG as effectively
What is the double Bohr effect?
In the mother: As CO2 passes into intervillous blood, pH decreases, decreasing affinity of Hb for O2.
In the fetus: CO2 is lost and pH rises, increasing the affinity of haemaglobin for O2.
How is a CO2 gradient set up to allow transfer of CO2 from the fetus to the mother?
Progesterone driven hyperventilation decreases the pCO2 in the mother’s blood, meaning CO2 is higher in the fetus.
What is the double haldane effect?
As Hb gives up O2 in the mother, it can accept increasing amounts of CO2. as the fetus accepts oxygen, CO2 is given up. Allows effective CO2 transfer
What shunts are present in the fetus?
Ductus venosus - bypasses the liver.
Foramen ovale - shunts blood from the right to the left atria of the heart.
Ductus arteriosus - shunts blood from right ventricle and pulmonary trunk to the aorta.
What two structures does the ductus venosus connect?
What oxygen saturation does the blood maintain due to this?
Umbilical vein and inferior vena cava.
~65%
What does the septum secundum form?
Crista dividens. Creates two streams of blood flow, with the majority flowing to the left atrium. Minor proportions flow to the right ventricle.
How does the fetus respond to hypoxia?
Slowing of fetal heart rate - chemoreceptors detect elevated pCO2 and decreased pO2 leading to vagal stimulation.
Redistribution of blood flow to heart and brain.
Which hormones stimulate fetal growth?
Insulin, IGF I and II, Leptin, EGF, TGF alpha.
What is asymmetrical growth restriction?
What is symmetrical growth restriction?
Head Sparing, Different body parts grow slower than others.
Reduced fetal size.
What produces amniotic fluid originally?
What takes over once fully formed?
Transudation through fetal membranes.
Urine production by the renal system.
What is amniotic fluid composed of?
98% water, electrolytes, urea, renin, languo (hair) and vernix caseosa (waxy cellular layer).
What is meconium?
What does this indicate if it is found in amniotic fluid?
Debris from swallowed amniotic fluid found in the GI tract. usually passed in the fetuses first movement.
Indicates fetal distress.
What is amniocentesis?
Why is this preferable to chorionic villi sampling?
Sampling of amniotic fluid containing fetal cells, used for fetal karyotyping and diagnosis of genetic conditions.
Has a lower risk of miscarriage than other methods such as chorionic villus sampling.
Why is fetal jaundice common?
Conjugation of fetal bilirubin is handled by the placenta. Fetus cannot conjugate bilirubin itself.
What is crown rump length?
Measurement of the top of the head to the bottom of the rump, used to assess fetal growth. Measured between 7 and 13 weeks.
What assessments can be done to assess fetal wellbeing?
Fetal movements during second trimester,
Symphysis fundal height,
Ultrasound scan.
When is a fetal USS done routinely and why?
Around 20 weeks, as most fetal systems are developed at this time and can be assessed for abnormality, and termination of pregnancy is still possible.
What is Biparietal diameter?
Distance between the parietal bones of the fetal skull seen on ultrasound. Used to date pregnancy in trimester 2 and 3.
What measurements are used alongside biparietal diameter to asses fetal growth?
Abdominal circumference and femur length.
what is average birth weight?
What weights are considered as growth restriction and macrosomia?
3.5kg average.
<2.5kg fetal growth disturbance.
>4.5kg macrosomia.
What structure fuses to separate the oesophagus and the trachea?
Tracheoesophageal septum.
What occurs in the pseudoglandular stage of lung development?
Duct systems begin to form within bronchopulmonary segments. Begins formation of the bronchioles.
What happens during the cannaliculi revolution stage of embryological development?
Formation of respiratory bronchioles.
What happens during the terminal sac stage of respiratory development?
Terminal sacs begin to bud from respiratory bronchioles, and differentiation of alveolar cells occurs into type 1 and 2 pneumoctes.
When does production of surfactant begin?
What is significant about this?
Terminal sac stage - 24 weeks.
Fetus is only viable after this point. Cut off point of abortion.
How is respiratory distress syndrome prevented?
Glucocorticoid treatment of the mothe during pregnancy stimulates surfactant production in the fetus.
When is definitive fetal heart rate achieved?
At what rate is this often set?
15 weeks.
110-160bpm.
Oligohydramnos signifies a defect in which fetal system?
What about polyhydrammos?
Renal.
GI or uroplacental.
When do corticospinal tracts responsible for voluntary movement begin development?
When does myelination of the brain occur?
4 months.
9 months, continues after birth.
What is quickening?
Increase in fetal movements, often felt by the mother. Usually noticed from 17 weeks onwards.
