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Flashcards in Repro Session 9 Deck (152):
1

What is the organogenetic period of human development?

Embryonic period

2

Describe growth in the embryonic period.

Foetal growth is very small but placental growth is large

3

Broadly describe the foetal period.

Growth and physiological maturation of structures established in the embryonic period

4

When is the embryonic period?

3-9 weeks after fertilisation

5

When is the foetal period?

9-38 weeks post fertilisation

6

Why is human pregnancy considered to be 40 weeks when human gestation is 38 weeks?

Can be +/- 2 weeks due to natural variation but this is masked by using the date of the LMP to calculate pregnancy weeks

7

Why is using LMP to date pregnancy prone to inaccuracy?

Irregularity of menstrual cycles and confusion with implantation bleeding

8

During which periods does CRL increase rapidly?

Pre-embryonic, embryonic and early foetal

9

When is increase in CRL most striking?

Months 3-5

10

Describe how the body proportions of the foetus changes during development.

At 9 weeks head = 0.5 CRL, reducing to 0.3 around 20 weeks and reaching 0.25 at term

11

What happens after week 9 that allows the body proportions of the foetus to near those seen in the adult?

Acceleration of body and lower limb growth

12

What CRL would be expected at 9 weeks?

5 cm

13

What CRL would be expected at 9, 12, 16 and 38 weeks respectively?

5, 8.5, 16 and 36 cm

14

Around what time does the face become more distinguished and the limbs reach their relative lengths?

Week 12

15

Briefly describe the 16 week old foetus.

Weighs less than 500 g and is covered in lanugo with head and eyebrow hair visible

16

When does weight gain increase rapidly in utero?

2nd half of intrauterine life, especially during mid- and later foetal periods

17

When is 50% of full term weight added to the foetus?

Mid and late foetal periods

18

What deposition dominates in weight gain of the early foetus?

Protein

19

Does protein deposition always dominate in weight gain of the foetus?

No, adipose deposition takes over in late foetal stages

20

Why might a pre-term baby be unable to maintain a constant body temperature?

Lack of brown adipose tissue for thermoregulation due

21

What are non-pathological causes of low birth weight?

Prematurity or constitutionally small

22

How is a SFD differentiated from IUGR?

By doppler- abnormal in IUGR

23

What happens if a foetus is SFD and has an abnormal Doppler scan at >36 weeks?

Labour is induced or C-section performed

24

How is IUGR identified preterm managed?

Regular review

25

Why is obstetric USS performed in early pregnancy?

Confirm gestation, pregnancy site, number of foetuses, age and rule out ectopics

26

When is USS in early pregnancy usually performed?

9-12 weeks

27

What allows a more accurate ageing of a foetus than calculation of pregnancy from LMP?

CRL between weeks 7-13

28

What method can be used for early obstetric USS if there are concerns?

Transvaginal

29

When is obstetric USS routinely performed?

20 weeks

30

What is the 20-week obstetric USS also known as?

Anomaly scan

31

Why is an obstetric USS performed at 20 weeks?

To assess foetal growth and identify congenital malformations as all are detectable at this stage

32

How does a 4D USS scan differ from a 3D scan?

Includes time dimension, gives better resolution image

33

What measurements of the foetus are used in pregnancy?

Biparietal diameter, abdominal circumference, femur length, foot length

34

Why are biparietal diameter, abdominal circumference and femur length used together when assessing foetal growth?

Used for dating and to identify asymmetrical growth restriction

35

What does asymmetrical growth restriction usually spare?

Head

36

What is symphysis-fundal height?

Measurement made with tape measure between maternal public symphysis and uterine fundus to assess uterine expansion out of the pelvis

37

What is the average birth weight?

3500 g

38

What birth weight is suggestive of a growth restriction?

Less than 2500 g

39

What birth weight is determined as macrosomia?

>4500 g

40

What does macrosomia indicate in the mother?

Maternal diabetes

41

What development of the respiratory system takes place in the embryonic period?

Bronchopulmonary tree from diverticulum that appears at week 4

42

How many generations of subdivisions are made in the bronchopulmonary tree by the end of the 6th month of development.

17

43

How many bronchopulmonary divisions arise postnatally?

6

44

When is the pseudo glandular stage of respiratory system development?

Weeks 8-16

45

What happens in the pseudo glandular stage of respiratory development?

Duct systems begin to form within bronchopulmonary segments to create bronchioles

46

What epithelium lines the bronchioles and their buds during the pseudo glandular stage?

Columnar

47

When is the canalicular stage of respiratory development?

Weeks 16-26

48

What happens in the canalicular stage of respiratory development?

Budding from bronchioles to form respiratory bronchioles

49

When is the terminal sac stage of respiratory development?

Weeks 26-term

50

What happens in the terminal sac stage of respiratory development?

3-6 alveolar ducts from each respiratory bronchiole end in terminal sacs that bud from the bronchioles, surrounded by flat alveolar cells in close contact with capillaries

51

When are there enough respiratory components to guarantee adequate gas exchange if delivery takes place?

End of the 7th month

52

What happens to type I pneumocytes lining terminal sacs during the last 2 months of development?

Become thinner so surrounding capillaries protrude to create the blood-air barrier

53

Are mature alveoli present before birth?

No

54

When do type II pneumocytes develop?

Month 6

55

What molecule is surfactant rich in?

Phospholipid

56

What is the composition of the fluid filling the lungs in T2 and T3?

High [Cl-], small amount of protein, mucus from bronchial glands and surfactant

57

What is the action of the significant increase in surfactant production in the last 2 weeks on the lungs?

Activates alveolar macrophages

58

What is the purpose of foetal breathing movements?

Condition respiratory musculature and draw in amniotic fluid

59

What is neonatal respiratory distress syndrome?

Insufficient surfactant production --> high blood-air surface tension --> alveoli collapse on expiration

60

What do partially collapsed alveoli in neonatal respiratory distress syndrome contain?

Fluid high in protein, hyaline membranes and lamellar bodies

61

How is neonatal respiratory distress syndrome managed if pre-term delivery is unavoidable?

Give glucocorticoids to mother to increase foetal surfactant production and administer synthetic surfactant to neotnate

62

What is the foetal circulation arranged to ensure?

Oxygenated blood of ~80% sats from umbilical vein is circulated around foetus and retuned via umbilical artery at ~58%

63

What range should foetal HR lie within from ~15 weeks onwards?

120-160 bpm

64

What are the three shunts present in the foetal CVS?

Ductus venosus, foramen ovale, ductus arteriosus

65

What guides flow of blood through foramen ovale?

Valve of IVC

66

What guides a small amount of bloodflow from the RA to RV to allow for lung development?

Crista dividens

67

Where does ductus arteriosus shunt blood from and to?

From PT to aorta

68

When does foetal kidney function begin?

Week 10

69

What is the result of renal agenesis in utero?

Oligohydramnios

70

What are the possible consequences of oligohydramnios?

Club foot, lung hypoplasia

71

Is foetal kidney function necessary for survival in utero?

No

72

What is hydramnios?

Excess amniotic fluid

73

What are the primary causes of hydramnios?

Idiopathic, maternal diabetes, CNS deformity, GI defects (prevented swallowing of neural/musclar cause)

74

What is the first system to start and last system to finish developing in utero?

CNS

75

What are corticospinal tracts required for?

Coordinated voluntary movements

76

When do coordinated voluntary movements of the foetus begin?

4th month

77

What is 'quickening'?

Patterns of foetal movement that are detectable by the mother

78

When does quickening usually arise?

17 weeks onwards

79

What does the start of quickening depend on?

Number of previous pregnancies, size of baby, size of mother

80

Can foetal movements be identified before 8 weeks?

No

81

Why do breathing and suckling movements start in the 4th month of development?

To 'practise' for postnatal life

82

Why are humans neurologically immature at birth?

Due to implications on head size and vaginal delivery

83

When does myelination of the brain start?

9th month

84

What evidence of postnatal brain myelination is there in the neonate?

Increasing infant mobility in the 1st year

85

What determines viability of a pre-term baby?

Development of the respiratory and CNS

86

When does myelination start in the spinal cord?

20 weeks

87

When do the gyri and sulci arise?

28 weeks

88

What causes development of the gyri and sulci?

Cerebellar hemispheres grown larger than the skull

89

What respiratory event occurs at the same time as the onset of myelination in the brain?

Increased surfactant production

90

What forms the maternal arm of the materno-foetal exchange system at the placenta?

Uterine arteries and veins emptying into intervillous spaces

91

What forms the foetal arm of the materno-foetal exchange system at the placenta?

Umbilical arteries branching into foetal capillaries in the chorionic villi and umbilical vein

92

How does foetal pO2 compare to the maternal value?

Foetal = 4 kPa, maternal = 11-13 kPa

93

What allows the foetal oxygen content to be sufficient at the partial pressure seen in utero?

Foetal haemoglobin variant, foetal Hb levels > adult male levels, increased maternal 2,3-DPG levels, foetal haematocrit levels > adult levels

94

Does the foetal haemoglobin variant bind as effectively as the adult variant to 2,3 DPG?

No

95

How do hormones in the mother contribute to the concentration gradient between the maternal and foetal circulations?

Progesterone causes hyperventilation creating a physiological respiratory alkalosis that results in lowered maternal pCO2

96

Describe the Bohr effect in the mother that aids gas exchange at the placenta.

CO2 moves into intervillous blood causing reduced pH and lowering the affinity of Hb for O2

97

Describe the Bohr effect seen in the foetus that aids gas exchange at the placenta.

Foetal CO2 is lost causing an increased pH resulting in an increased affinity of Hb for oxygen

98

What is the difference between the double Bohr and Haldane effects?

Bohr-determined by pCO2, Haldane-determined by [O2]

99

Describe the double Haldane effect.

In the maternal blood Hb releases O2 and therefore accepts more CO2 whilst in the foetus more CO2 is released so it can accept more O2

100

What prevents local alterations of pCO2 in the materno-foetal circulation?

Double Haldane effect

101

Where does the ductus venosus connect?

Umbilical vein to IVC

102

What is the purpose of the ductus venosus?

Cause blood entry to the RA bypassing the liver so that sats only drop by 5%

103

Why is the liver hugely metabolically active in utero?

Synthesising haematological and immunological proteins

104

Does the foetal liver have hepatobiliary function?

No

105

What regulates the small amount of blood entry into the liver sinusoids in utero?

Sphincter within ductus venosus

106

What prevents heart overload in the foetus during uterine contractions?

Closure of the sphincter in ductus venosus

107

Why might physiological jaundice be seen at birth?

Foetal liver does not have hepatobiliary function so cannot conjugate bilirubin

108

What forces the 2-leaved foramen ovale apart?

p(RA) > p(LA)

109

What forms the crista dividens?

Free border of septum secundum

110

What effect does the crista dividens have on bloodflow?

Divides into 2 streams

111

Where does the minor steam of blood from the crista dividens flow?

To the RV to mix with deoxygenated blood from the SVC

112

What causes the sats of blood in the LA to be around 60%?

Small amount of pulmonary venous return

113

What shunts blood from the PT into the aorta?

Ductus arteriosus

114

Why is blood shunted from the PT into the aorta distal to the supply to the head and heart?

Allows pulmonary circulation to develop without significantly reducing oxygen sats

115

When are transient episodes of hypoxia seen in utero?

During labour when uterine contractions compress the umbilical vein

116

What happens to bloodflow in the foetus during transient episodes of hypoxia?

Redistributed from GI tract, kidneys and limbs to the heart and brain

117

What are the effects of foetal chemoceptors detecting low pO2?

Vagal stimulation resulting in bradycardia

118

Why does foetal vagal stimulation result in bradycardia?

To reduce oxygen demands

119

What can chronic hypoxaemia lead to in the foetus?

Growth restriction and behavioural changes

120

What causes behavioural changes due to chronic hypoxaemia in the foetus?

REM sleep pattern disruption

121

What are the necessary hormone for foetal growth?

Insulin, human placental lactogen, leptin, IGFI, IGFII, EGF, TGF-alpha

122

What type of cellular growth is seen at 0-20 weeks?

Hyperplasia

123

What type of cellular growth is seen at 20-28 weeks?

Hyperplasia and hypertrophy

124

What type of cellular growth is seen at 28 weeks to term?

Hypertrophy

125

What type of growth restriction is seen at 0-20 weeks?

Irreversible symmetrical

126

What type of growth restriction is seen at 28 weeks to term?

Reversible asymmetrical

127

Where is foetal leptin produced?

Placenta

128

What do mutations to IGFI gene result in?

IUGR and growth retardation after birth

129

Which growth hormone dominated in T2 and T3?

IGFI

130

What effects does IGFI have?

Mitogenic and anabolic

131

Is IGFI or II nutrient-independent?

IGFII

132

What is the benefit of IGFII dominating foetal growth in T1?

Nutrient independent so is not affected by maternal nutritional status that may be poor due to nausea and vomiting

133

What is Barker's hypothesis?

Nutritional and hormonal status during foetal life can influence adult health

134

What does Barker's hypothesis suggest IUGR leads to?

Obesity, hypertension, hyoercholestrolaemia, CVD, T2DM

135

What is the purpose of amniotic fluid?

Allow for foetal movements, prevent adherence of embryo to amnion and protection from jolts

136

Where is amniotic fluid derived in early pregnancy?

In part by amniotic cells but primarily from maternal blood

137

When does the foetus begin to swallow amniotic fluid?

Beginning of the 5th month

138

When does the foetal kidney start to contribute towards amniotic fluid volume?

9 weeks

139

What foetal system other than the urinary system contributes to amniotic fluid volume?

Respiratory

140

How does the volume of amniotic fluid progress through pregnancy?

10 ml @ 8 weeks, 1l @ 38 weeks, reduces post-EDD

141

Why does amniotic fluid volume decrease post-EDD?

Senescence of placenta

142

What volume can the foetal kidneys contribute to the amniotic fluid in T3?

Up to 800 ml

143

What is the composition of amniotic fluid?

98% water, electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones, foetal cells, lanugo, vernix caseosa

144

What is vernix caseosa?

Covering of skin from foetal surfactant that water-proofs the skin

145

What forms meconium?

Bile and intestinal secretions, creatinine, urea, rening glucose, hormones, foetal cells, lanugo and vernix caseosa

146

What is meconium?

First stool passed by the neonate

147

When may meconium leak into the amniotic cavity?

Foetal distress

148

How does amniotic fluid enter the foetus?

Intramembranous across placenta and foetal membranes, through lungs and by swallowing

149

How does amniotic fluid exit the foetus?

As urine, from the lungs and head

150

How does amniotic fluid move out of the amniotic cavity?

Transmembranous

151

Describe the process of amniocentesis.

Fine-gauge needle under US guidance to remove amniotic fluid at 15 weeks

152

What is amniocentesis used for?

Prenatal diagnosis of chromosomal abnormalities, CMV, toxoplasmosis, SCD, thalassaemia and CF