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MRCOG Part one > Fetal physiology > Flashcards

Fetal physiology Flashcards

1
Q

How is cardiac output calculated in the fetes?

A

Combined ventricular output x HR

Hb: Not equal distribution of output from L+R ventricle

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2
Q

How does the fetus increased CO and why?

A

Increased HR

Little function reserve of the heart as is less compliant than adult heart/less contractile tissue (30% vs 60%)

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3
Q

What are the main fuels used in cardiac metabolism in the fetes? how is it compare to adult

A

Adult: long chain fatty acid, hypoxis glucose/lactate
Fetus: Lactate and carbohydrate

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4
Q

How does FHR change with increased gestation

A

Decreases

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5
Q

What factor increase FHR

A 
Catecholamines 
Sympathetic 
Hypoxia 
Pyrexia 
Tocolysis 
Arrythmia
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6
Q

What factor decrease FHR

A 
Vagal
Hypoxia 
Opiates
Heart block 
Cord compression
Placental abruption 
Maternal hypotension 
uterine hyperstimulation
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7
Q

What is the definition of an acceleration?

A

Increased of 15 beats/minute for at least 15 seconds

converse is true for deceleration

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8
Q

What is the depth of the baroreceptor a reflection of?

A

Baroreceptor stimulation (not hypoxaemia)

fetal wellbeing should therefore be base on baseline rate, variability and presence of acceleration

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9
Q

What transition cardiac events are seen at birth

A

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

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10
Q

What are the 3 shunts seen in utero? What do they connect?

A

Ductuc venous - umbilical vein blood to IVC
Foramen ovale - R to L atrium
Ducuts arteriosis - PA to aorta

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11
Q

How does the foremen ovale act as a valve?

A

Overlap of septum secundum over the septum primum

High pressure in R atrium ensures value is maintained open for R to L shunt.

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12
Q

How is oxygenated and deoxygenated bloods divided?

A

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

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13
Q

What factors keep the ductus arteriosis open?

A

Vasodilator effects of prostaglandin (PGE1 and PGE2), prostacyclin (PGI2) and reduced fetal oxygen tension

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14
Q

When should the ductus arteriosis close? What can be given for patent ductus arteriosis?

A

2 days after birth (higher systemic resistance and reduced pulmonary resistance)
Indometacin (prostaglandin)

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15
Q

When does the ductus venosus close?

A

1-3 weeks for term infants

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16
Q

When does the foramen ovale close? What complications can occur if it does not?

A

1 year

Paradoxical embolic event

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17
Q

What are the 5 stages of fetal lung development

A
  1. Embryonic - until 7 weeks, main branchus
  2. Pseudoglanduar 7-17 - branching of airways + blood vessels
  3. Canalicular 17-27 weeks - formation of acini, gas exchanging parts
  4. Saccular 28-36 - enlargement of peripheral airways
  5. Alveolar 36 to 2 yrs gest - definitive alveoli
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18
Q

Fetal breathing movements are important for what? Reduced by?

A

Regulate lung growth/lung fluid regulation

Decreased hypoxia, ETOH consumption and sedative drugs

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19
Q

When is lung fluid formed and where? Its significance?

A

From canalicular stage from alveolar epithelial cells

Essential for lung development, if limited lung fluids of amniotic fluid → lung hypoplasia

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20
Q

What is lung surfactant made from & where?

A

Lipoproteinmade by type II penumocytes
90% lipids (mostly DPPC)
10% protein A-D

21
Q

Role of lung surfactant

A

Reduce surface tension
B+C - spread over alveoli
A+D - innate immunity

22
Q

Why are male infants more likely to suffer from respiratory distress?

A

Androgens delay lung maturity

23
Q

when are fetal WBCs and platelets first produced?

A

6 weeks

24
Q

Is embryonic or fetal haemoglobin controlled by EPO?

A

Embryonic - no
fetal - yes

EPO from 20 weeks, increases in hypoxia/placental insufficiency

25
Q

What are the embryonic haemoglobins?

A

Hb Gower1
Hb Gower2
Hb Portland

26
Q

What does HbF consist of compared to adult haemoglobin

A

HbF - 2 alpha and 2 gamma chains

Adult: 2 alpha and 2 beta

27
Q

When does HbF take over embryonic haemoglobin?

A

10 weeks, peaks at 32 weeks

28
Q

What does Adult Hb overtake HbF

A

between brith and 12 weeks of PN life

persists until 3-6 months PN

29
Q

What is bound to adult Hb that makes it have a lower oxygen affinity than HbF

A

2,3-DPG

30
Q

Which way on the oxygen dissociation curve is HbF than adult?

A 
To the left
Lower p50 (3.6 vs 4.8)
31
Q

What is the purpose and basis of the kleihauer test?

A

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

32
Q

Which stem cells give rise to B lymphocytes and in which organ?

A

Lymphoid stem cells, liver at 12 weeks

33
Q

Which stem cells give rise to T cells and in which organ?

A

Lymphoid stem cells, thymus at 14 weeks

34
Q

From before what gestation is the immune system immature

A

32 weeks, from this time rapidly approaches term infant

35
Q

What is the discussed benefit of late cord clamping below level of placenta

A

Increase in blood volume and red cell mass

  • some argue to much causes hyperbilirubinaemia
36
Q

How much of fetal cardiac output goes to the kidneys?

A

2-3%

37
Q

What are the main contributors to the amniotic fluid >18/40 and <16/40

A

> 18/40 urine production

<16/40 skin and placenta

38
Q

Why is fetal urine hypotonic?

A

Fetal kidney had limited ability to concentrate urine, increase with gestation - infant babies less able to maintain fluids/electrolytes

39
Q

What is the importance of in-utero swallowing?

A
  1. Amniotic fluid regulation

2. Prevents bowel obstruction in fetus

40
Q

What is the composition of meconium?

A 
Water 75%
Intestinal secretions
Squamous cells 
Lanugo hair 
Bile pigments 
pancreatic enzyme a
blood
41
Q

What % of babies pass meconium in the first 48hrs?

A

98%

42
Q

What % of babies born have meconium what if post term?

A
  • 12% all pregnancies

- 30% post term pregnancies

43
Q

What % of babies born with meconium stained amniotic fluid develop meconium aspiration syndrome?

A

5%

44
Q

Until what gestation is the skin permeable to water?

A

Mid-pregnancy - increased keratin and connective tissue

45
Q

When does the sleep/wake cycle begin?

A

30 weeks

46
Q

When does the mother first perceive feral movements?

A

Primip 16 weeks

Multiparous 24 weeks

47
Q

How does the amount of amniotic fluid change in pregnancy?

A

12 weeks: 50ml
16 weeks: 150ml
increases 50ml per week until 34 weeks - 1000ml, then decreased 500ml before term

48
Q

What % of the amniotic fluid is water?

A

98%

MRCOG Part one (28 decks)

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