Fetal Physiology Flashcards Preview

ESA 4 - Reproductive System > Fetal Physiology > Flashcards

Flashcards in Fetal Physiology Deck (99):
1

Where does materno-fetal exchange occur? 

At the placenta 

2

What does circulation around the fetal body culminate in? 

Umbilical arteries and umbilical veins

3

How is oxygenated blood carried to the fetal body?

Via the umbilical vein

4

How is deoxygenated blood and products of fetal metabolism carried from the fetal body? 

Umbilical arteries 

5

Where do the umbilical arteries and veins join with the fetal capillaries?

At the chorionic villi 

6

Where does gas exchange between the mother and fetus occur? 

At the tips of the chorionic villi 

7

What is the function of the chorionic villi? 

Increase the surface area 

8

What happens to uterine arteries?

They branch into the spiral arteries, which spill maternal blood into blood lakes

9

What does the uterine vein do? 

Drains maternal blood lakes into the intervillous spaces

10

What are the requirements for gas exchange at the placenta? 

  • Diffusion barrier must be small
  • Gradient of partial pressures required

 

11

What happens to the size of the fetal barrier as pregnancy proceeds?

It decreases - the structure of the placenta adapts as the metabolic needs increase

12

How does the structure of the placenta adapt to optimise gas exchange? 

Number of layers decreases to the minimum amount required to keep the circulations seperate 

13

How much does maternal pO2 increase during pregnancy? 

Only marginally 

14

What is the result of the maternal pO2 increasing only marginally during pregnancy? 

The fetal pO2 must be lower than the maternal pO2 to make the gradient work, and so is adapted to tolerate a much lower pO2 

15

What is the pO2 of the fetus? 

4kPa

16

What factors increase fetal O2 content? 

  • Fetal haemoglobin variant 
  • Fetal haematocrit is increased over that of the adult 
    • Increased maternal production of 2,3 DPG
  • Double Bohr effect
  • Increased concentration gradient by physiological hyperventiation 
  • Double Haldane effect

 

17

What is the predominant form of haemoglobin in the fetus from 12 weeks - term? 

HbG

18

What subunits are in HbG?

2 alpha and 2 gamma 

19

Why does HbG have a greater affinity for oxygen than adult haemoglobin? 

Because it doesn't bind 2,3-DPG as effectively as HbA

20

What is the increased maternal production of 2,3-DPG secondary to? 

Respiratory alkalosis of pregnancy 

21

What is the result of the double Bohr effect? 

Speed sup process of oxygen transfer 

22

How is the double Bohr effect produced in the fetus? 

  • On the maternal side, as CO2 passes into the intervillous blood, pH decreases, producing the Bohr effect, which decreases the affinity of Hb for O2, so more likely to give O2 up 
  • On the fetal side, CO2 is list, and pH rises. giving the Bohr effect and increasing addinity of Hb for O2 

 

23

What drives hyperventilation in pregnancy? 

Progesterone

24

What is the result of the physiological hyperventilation in pregnancy on gas exchange? 

There is a lower pCO2 in maternal blood, as more CO2 has been blown off, and so there is an increased concentration gradient because the fetus is producing CO2, so relatively higher [pCO2] in fetal blood 

25

What gives the double Haldane effect? 

As Hb gives up O2, it can accept increasing amounts of CO2, and the fetus gives up CO2 as O2 is accepted 

26

How does the fetal circulation receive oxygenated blood? 

From the mother, via the placenta in the umbilical vein 

27

Why does the fetal circulation not get its oxygen from the lungs? 

Because the lungs are non-functional, and so they are bypassed 

28

How does blood in the fetal circulation return to the placenta? 

Via the umbilical arteries 

29

What circulatory shunts does the fetus have? 

  • Ductus venosus
  • Foramen ovale
  • Ductus arteriosus 

 

30

What does the ductus venosus bypass? 

The liver 

31

What path does blood take due to the ductus venosus? 

The DV connects the umbilical vein carrying oxygenated blood to the IVC, then blood enters the right atrium 

32

What is the purpose of shunting blood around the liver? 

It ensures that saturation is mostly maintained, dropping from 70% to 65%

33

Why is shunting around the liver required to maintain oxygen saturation of the blood? 

Becasue the liver is very metabolically active, so if the blood with the highest pO2 passed through it, would take most of the oxygen

34

What does the foramen ovale bypass? 

The right ventricle and lungs 

35

How does the foramen ovale function? 

Right atrial pressure is greater than that in the left atrium, so forces the leaves of the FO apart, and blood flows into the LA

36

What forms the crista dividens? 

The free border of the septum secundum

37

What is the crista dividens? 

A small anatomical specialisation which optimises flow to the LA, by creating two streams of flow

38

Where does the majority of the blood go from the right atrium?

The left atrium 

39

What is the saturation of the blood entering the LA? 

Approx 60%

40

What happens to the blood shunted to the left atrium? 

It is pumped to the left ventricle, and then the aorta 

41

What is the result of the shunting of blood into the left atrium? 

The heart and brain get a large share of the oxygen 

42

Other than from the RA, where else does the LA recieve blood from? 

Recieves a small amount form the pulmonary venous return

43

Is the blood entering the left atrium from the pulmonary venous return oxygenated or deoxygenated? 

Deoxygenated, it is the blood from the metabolic output of the developing lungs 

44

What happens to the minor portion of blood from the RA that flows to the RV?

It mixes with deoxygenated blood from the SVC

45

Why must some blood flow into the RV? 

To allow development, as the muscle needs something to pump against 

46

What does the ductus arteriosus do? 

Bypasses the lungs from the right ventricle 

47

Where does the ductus arteriosus shunt blood from? 

The RV and PT, to the aorta 

48

Where does the blood shunted by the ductus arteriosus enter the aorta? 

Distal to the supply to the head

49

Why is it important that the blood shunted by the ductus arteriosus enters the aorta distal to the supply to the head? 

It minimises drop in O2 saturation, and therefore minimises dilution by deoxygenated blood 

50

What adaptations does the fetus have to manage transient decreases in oxygenation? 

  • HbF and transient decreases in oxygenation
  • Redistribution of flow to protect supply to the heart and brain 
  • Fetal heart rate slows in response to hypoxia, to reduce O2 demand

 

51

What is the trade-off with redistribution of flow to protect the supply to the heart and brain? 

Reduces supply to GIT, kidneys, and limbs 

52

What does vagal stimulation lead to in the fetus? 

Bradycardia 

53

What is the clinical importance of vagal stimulation leading to bradyvardia in the fetus? 

During delivery, contractions of the vagina constricts the spiral arteries, and thus constricting the blood lakes, reducing flow to the fetus, so must check fetal HR during delivery 

54

What can chronic hypoxia of the fetus be caused by?

Anything impairing normal blood supply to the placenta 

55

Give an example of where chronic hypoxia of the fetus may occur? 

In women who smoke 

56

What does chronic hypoxia of the fetus lead to? 

  • Growth restriction 
  • Behavioural changes 

 

57

What behavioural changes are seen in chronic hypoxia of the fetus? 

  • Less movement
  • Less evidence of REM sleep state

58

What hormones are required for fetal growth? 

  • Insulin
  • IGF I and IGF II 

 

59

is IGF I nutrient dependant or independant? 

Dependant 

60

When does IGF I dominate? 

In T2 and T3

61

Is IGF II nutrient dependant or independant? 

Independant 

62

When does IGF II dominate? 

T1

63

What is the function of leptin in the fetus? 

Promotes utilisation of nutrients 

64

What produces leptin in the fetus? 

Placenta 

65

How does fetal dependancy on growth hormone differ from that of the newborn? 

Fetus less dependant 

66

What can have an effect on fetal growth during pregnancy? 

Nutrition 

67

What can malnutrition cause in pregnancy? 

Symmetrical or asymmetrical growth restriction

68

What is Barkers hypothesis, or the 'developmental origins of health and disease' hypothesis? 

Maternal nutrition can cause symmetrical or asymmetrical growth restriction

69

What mechanisms underlie Barkers hypothesis? 

Mechanisms not well understood, but could be placental adapative responses to alterations in hormonal and/or nutritional status - changes in fetal physiological to match nutrient availability

70

What is the dominant cellular growth mechanism from 0-20 weeks? 

Hyperplasia 

71

What is the dominant cellular growth mechanism from 20-28 weeks? 

Hyperplasia and hypertrophy 

72

What is the dominant cellular growth mechanism from 28 weeks - term? 

Hypertrophy

73

What does the amniotic sac do? 

Encloses the embryo/fetus in amniotic fluid 

74

What is the role of amniotic fluid? 

  • Protection
  • Contributes to the development of the lungs 

 

75

How does amniotic fluid contribute to the development of the lungs? 

Practice breathing movements takes fluid into the lungs 

76

What is the volume of the amniotic fluid at 9 weeks? 

10mls

77

 What is the volume of amniotic fluid at 38 weeks? 

Approx 1L

78

What happens to the volume of amniotic fluid post-EDD? 

It falls 

79

Why does the volume of amniotic fluid fall post-EDD? 

Because the placenta is designed to last the gestational period, and after that, the function declines 

80

When does urine production start in the fetus? 

9 weeks 

81

How much urine is produced per day in T3? 

Up to 800ml

82

Draw a diagram illustrating amniotic fluid production and recycling

83

What is the result of the amniotic fluid being inhaled into the fetal lungs? 

The lungs bathe in the fluid 

84

What happens in the intramembranous pathway? 

The placeta and fetal mmebranes take amniotic fluid back into the fetus 

85

What happens when amniotic fluid is swallowed? 

  • Absorbs water and electrolytes
  • Debris accumulates in the gut as meconium 

 

86

What does meconium contain? 

Debris from the AF, plus intestinal secretions including bile 

87

When should meconium be passed? 

After delivery 

88

What is meconium stained amniotic fluid a sign of? 

Fetal distress

89

What can meconium in the amniotic fluid cause? 

Respiratory distress

90

What % of amniotic fluid is water? 

98%

91

Other than water, what is in amniotic fluid? 

  • Electrolytes
  • Creatinine
  • Urea
  • Bile pigments
  • Glucose
  • Hormones
  • Fetal cells
  • Lanugo
  • Vernix caseosa

 

92

What is the purpose of the vernix caseosa? 

Waterproofs the fetus, ensuring that fetal skin is not damaged by exposure to fluid during gestation

 

93

What is amniocentesis? 

Sampling of amniotic fluid to allow for collection of fetal cells 

94

What is amniocentesis uesd for? 

Diagnostic testing, particularly fetal karyotyping

95

What is the problem with amniocentesis? 

Invasive procedure

96

How does the risk of amniocentesis compare with chorionic villi sampling? 

Less invasive, so lower risk of miscarriage with amniocentesis

97

How is clearance of bilirubin conducted in the fetus? 

Handled efficiently by the placenta 

98

Why does fetal bilirubin need to be handled by the placenta? 

Because the fetus cannot conjugate bilirubin due to immaturity of liver and intestinal processes for metabolism, conjugation, and excretion 

99

What is the result of a baby being unable to conjugate bilirubin? 

Physiological jaundice is common