Fetal physiology Flashcards
How is cardiac output calculated in the fetes?
Combined ventricular output x HR
Hb: Not equal distribution of output from L+R ventricle
How does the fetus increased CO and why?
Increased HR
Little function reserve of the heart as is less compliant than adult heart/less contractile tissue (30% vs 60%)
What are the main fuels used in cardiac metabolism in the fetes? how is it compare to adult
Adult: long chain fatty acid, hypoxis glucose/lactate
Fetus: Lactate and carbohydrate
How does FHR change with increased gestation
Decreases
What factor increase FHR
Catecholamines Sympathetic Hypoxia Pyrexia Tocolysis Arrythmia
What factor decrease FHR
Vagal Hypoxia Opiates Heart block Cord compression Placental abruption Maternal hypotension uterine hyperstimulation
What is the definition of an acceleration?
Increased of 15 beats/minute for at least 15 seconds
converse is true for deceleration
What is the depth of the baroreceptor a reflection of?
Baroreceptor stimulation (not hypoxaemia)
fetal wellbeing should therefore be base on baseline rate, variability and presence of acceleration
What transition cardiac events are seen at birth
Loss from placental circulation and shunts
Cardiac output can be measured as adult
Increase in myocardial contractility
Increased in L ventricular mass
Switch from lactate and carbohydrate to free fatty acid metabolism
What are the 3 shunts seen in utero? What do they connect?
Ductuc venous - umbilical vein blood to IVC
Foramen ovale - R to L atrium
Ducuts arteriosis - PA to aorta
How does the foremen ovale act as a valve?
Overlap of septum secundum over the septum primum
High pressure in R atrium ensures value is maintained open for R to L shunt.
How is oxygenated and deoxygenated bloods divided?
High velocity oxygenated blood from narrow umbilical vein is shunted toward foramen ovale via atrial septum (crrista dividens) 90% goes to coronary arteries
Low velocity deoxygenated enters right ventricle which is later suntan via duct arterisosus to descending aorta
What factors keep the ductus arteriosis open?
Vasodilator effects of prostaglandin (PGE1 and PGE2), prostacyclin (PGI2) and reduced fetal oxygen tension
When should the ductus arteriosis close? What can be given for patent ductus arteriosis?
2 days after birth (higher systemic resistance and reduced pulmonary resistance)
Indometacin (prostaglandin)
When does the ductus venosus close?
1-3 weeks for term infants
When does the foramen ovale close? What complications can occur if it does not?
1 year
Paradoxical embolic event
What are the 5 stages of fetal lung development
- Embryonic - until 7 weeks, main branchus
- Pseudoglanduar 7-17 - branching of airways + blood vessels
- Canalicular 17-27 weeks - formation of acini, gas exchanging parts
- Saccular 28-36 - enlargement of peripheral airways
- Alveolar 36 to 2 yrs gest - definitive alveoli
Fetal breathing movements are important for what? Reduced by?
Regulate lung growth/lung fluid regulation
Decreased hypoxia, ETOH consumption and sedative drugs
When is lung fluid formed and where? Its significance?
From canalicular stage from alveolar epithelial cells
Essential for lung development, if limited lung fluids of amniotic fluid → lung hypoplasia
What is lung surfactant made from & where?
Lipoproteinmade by type II penumocytes
90% lipids (mostly DPPC)
10% protein A-D
Role of lung surfactant
Reduce surface tension
B+C - spread over alveoli
A+D - innate immunity
Why are male infants more likely to suffer from respiratory distress?
Androgens delay lung maturity
when are fetal WBCs and platelets first produced?
6 weeks
Is embryonic or fetal haemoglobin controlled by EPO?
Embryonic - no
fetal - yes
EPO from 20 weeks, increases in hypoxia/placental insufficiency
What are the embryonic haemoglobins?
Hb Gower1
Hb Gower2
Hb Portland
What does HbF consist of compared to adult haemoglobin
HbF - 2 alpha and 2 gamma chains
Adult: 2 alpha and 2 beta
When does HbF take over embryonic haemoglobin?
10 weeks, peaks at 32 weeks
What does Adult Hb overtake HbF
between brith and 12 weeks of PN life
persists until 3-6 months PN
What is bound to adult Hb that makes it have a lower oxygen affinity than HbF
2,3-DPG
Which way on the oxygen dissociation curve is HbF than adult?
To the left Lower p50 (3.6 vs 4.8)
What is the purpose and basis of the kleihauer test?
to assess fetal red cells in maternal circulation if ABO incompatible.
HbF more resistant to acid/alkali than HbA
Mothers blood washed in acid bath, washes away HbA - can count HbF
Which stem cells give rise to B lymphocytes and in which organ?
Lymphoid stem cells, liver at 12 weeks
Which stem cells give rise to T cells and in which organ?
Lymphoid stem cells, thymus at 14 weeks
From before what gestation is the immune system immature
32 weeks, from this time rapidly approaches term infant
What is the discussed benefit of late cord clamping below level of placenta
Increase in blood volume and red cell mass
- some argue to much causes hyperbilirubinaemia
How much of fetal cardiac output goes to the kidneys?
2-3%
What are the main contributors to the amniotic fluid >18/40 and <16/40
> 18/40 urine production
<16/40 skin and placenta
Why is fetal urine hypotonic?
Fetal kidney had limited ability to concentrate urine, increase with gestation - infant babies less able to maintain fluids/electrolytes
What is the importance of in-utero swallowing?
- Amniotic fluid regulation
2. Prevents bowel obstruction in fetus
What is the composition of meconium?
Water 75% Intestinal secretions Squamous cells Lanugo hair Bile pigments pancreatic enzyme a blood
What % of babies pass meconium in the first 48hrs?
98%
What % of babies born have meconium what if post term?
- 12% all pregnancies
- 30% post term pregnancies
What % of babies born with meconium stained amniotic fluid develop meconium aspiration syndrome?
5%
Until what gestation is the skin permeable to water?
Mid-pregnancy - increased keratin and connective tissue
When does the sleep/wake cycle begin?
30 weeks
When does the mother first perceive feral movements?
Primip 16 weeks
Multiparous 24 weeks
How does the amount of amniotic fluid change in pregnancy?
12 weeks: 50ml
16 weeks: 150ml
increases 50ml per week until 34 weeks - 1000ml, then decreased 500ml before term
What % of the amniotic fluid is water?
98%
