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BS - Reproductive System > Parturition > Flashcards

Parturition Flashcards

1
Q

What is meant by parturition?

A

It is the action of giving birth

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2
Q

What type of placentation is present in humans?

What does this mean?

Where is the placenta found?

A

Haemochorial placentation

Maternal blood is in direct contact with chorionic villi

The placenta is within the endometrium

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3
Q

What happens to the placenta as pregnancy progresses?

A

It is effective from the end of the first trimester

It senesces as pregnancy progresses

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4
Q

What are the 3 key roles of the placenta?

A
  1. hormone production
  2. acquisition of nutrients and removal of toxins
  3. gas exchange
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5
Q

What are the blood vessels of the placenta?

A

The umbilical vein and umbilical arteries are within the umbilical cord

The maternal venules and arterioles feed into maternal blood pools

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6
Q

What are the 2 parts of the placenta?

A

Foetal portion (chorion)

Maternal portion

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7
Q

What is the structure of the placenta like?

A

It consists of a few layers of cells that separate maternal from fetal blood

Folding villi give it a large surface area

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8
Q

What is the relation of the maternal blood pools to the foetal capillaries?

A

The foetal capillaries project from the umbilical artery (and vein) and are surrounded by maternal blood pools

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9
Q

What is the structure of a terminal villus on the foetal side of placental circulation?

Why is it like this?

A

The terminal vessels form a convoluted knot supplied by straight capillaries

The terminal dilatations mean blood flow is slower at the end of the capillaries, giving more time for exchange of metabolites between foetal and maternal blood

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10
Q

How does the oxygen saturation curve compare for foetal Hb?

A

The oxygen saturation curve is to the left

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11
Q

Why is foetal oxygen content higher than maternal oxygen content?

A
  1. foetus has higher Hb concentrations

2. HbF has a higher affinity for oxygen

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12
Q

How does foetal Hb concentration compare to maternal Hb concentration?

A

Foetal [Hb] is 17 g/dl

Maternal [Hb] is 12 g/dl

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13
Q

Why does HbF have a higher affinity for oxygen than HbA?

A

HbF contains 2 alpha and 2 gamma chains

2,3 DPG binds preferentially to beta chains in HbA - causing it to release more oxygen

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14
Q

What causes the foetal Hb curve to shift even further to the left?

A
  1. reduced binding of 2,3-DPG to gamma chains
  2. increased pCO2 and relative acidosis on maternal side

“double-Bohr” effect

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15
Q

When does foetal lung surfactant begin to be produced?

Where is it produced from?

A

Type II pneumocytes

They begin to produce surfactant from 24 weeks of pregnancy

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16
Q

What is the composition of foetal lung surfactant?

A
  1. phospholipids - PC and PG

2. apoproteins - SP-A, B, C, D

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17
Q

What is the function of foetal surfactant?

A

It decreases the surface tension at the air-liquid interface in the alveoli

This enables them to remain open at end-expiration

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18
Q

What stimulates production of foetal lung surfactant?

A

Fetal glucocorticoids and thyroid hormones (less so)

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19
Q

What does lack of foetal lung surfactant lead to?

Why is there a lack of surfactant?

A

Neonatal respiratory distress

Lack of surfactant may be due to prematurity or infection

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20
Q

What are the 2 therapies in place is there is a lack of foetal lung surfactant?

A
  1. promote production antenatally by administering maternal glucocorticoids
  2. replace in neonatal period through artificial surfactant
    e. g. Curosurf
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21
Q

What is the myometrium and what is its main function?

A

The middle layer of the uterine wall that consists mainly of smooth muscle cells

Its main function is to induce uterine contractions

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22
Q

What are the main structures in the myometrium?

A
  1. fasciculi
  2. smooth muscle bundles
  3. communicating bridges
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23
Q

How is an electrical potential generated in the myometrium?

A

Any cell can act as a pacemaker and generate an action potential

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24
Q

How is depolarisation mediated in the myometrium?

A

It is mediated by Ca2+ ions

Intercellularly through gap junctions

Intracellularly via Ca2+ channels and intracellular stores

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25
Q

How are action potentials propagated in the myometrium?

A

There can be a rapid action potential wave (global)

Then a slower intercellular calcium wave (local)

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26
Q

Why is it important that the myometrium has an electrical potential?

A

It enables coordinated and sustained contractions

Pregnancy requires a contraction that lasts 45-60 seconds

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27
Q

How does myometrial activity change during pregnancy and why?

A

There is a gradual preparation for labour

  1. rise in resting membrane potential
  2. increased intercellular coupling through gap junctions
  3. connexin expression
28
Q

What is the “diagnosis” of labour?

A

There are regular painful contractions

AND

Progressive effacement (opening/shortening) and dilatation of the cervix

AND

descent of the presenting part (head of the baby)

29
Q

What are the endocrine influences on parturition?

A
  1. release of cytokines
  2. cytokines lead to release of prostaglandins
  3. prostaglandins lead to release of oxytocin
  4. labour
30
Q

How is the foetus able to take oxygen from the mother’s blood?

A

Foetal haemoglobin has a much higher affinity for oxygen than maternal Hb

31
Q

How does the frequency of contractions change as pregnancy progresses?

A

At 28 weeks, contractions interval is 30 minutes

The contraction interval becomes progressively smaller as pregnancy progresses

32
Q

How many days, roughly, does pregnancy last?

A

280 days and slightly onwards

There is a large range of durations of pregnancy

33
Q

What are the endocrine influences that lead to cytokine production in labour?

A
  1. progesterone
  2. oestrogens
  3. DHEAS
  4. CRH (corticotrophin releasing hormone)

These are part of the stress response

34
Q

What are the stages in labour?

A

Firstly there are several stages of labour

This is followed by the cardinal movements of labour

35
Q

What is the diameter of the cervix during the first stage of labour?

How long does it last?

A

From 4 - 10 cm

It lasts for 12 - 24 hours

36
Q

What happens during the first stage of labour?

A
  1. contractions of uterine muscles force baby towards cervix
  2. cervical opening thins and widens as contractions of lengthwise uterine muscles pull it open
37
Q

How long does the second stage of labour last for?

When does it start?

A

It lasts from 1 - 4 hours

It starts when the cervix is dilated to 10 cm

38
Q

How are uterine contractions aided during the second stage of labour?

A

Uterine contractions are aided by mother’s involuntary pushes with abdominal wall muscles

39
Q

What else happens during the second stage of labour?

A
  1. head moves through dilated cervix and birth canal

2. shoulders and rest of body move through cervix and birth canal

40
Q

How long does the third stage of labour last for?

A

Up to 1 hour

41
Q

What happens during the third stage of labour?

A

The placenta separates from the uterine wall and is delivered through the vagina

42
Q

What is meant by the cardinal movements of labour?

A

The way in which the pelvis is shaped means that the baby has to make certain movements in order to be able to get out through the pelvis

43
Q

What are the cardinal movements of labour?

what the baby needs to do

A
  1. descent
  2. engagement (fixed into the pelvis so it doesn’t come back up)
  3. flexion
  4. internal rotation (so the smallest diameter of its head passes through the pelvis)
  5. extension (to get round the corner during birth)
  6. external rotation
  7. expulsion
44
Q

In what ways does the baby have to adapt to life outside the uterus?

A
  1. foetal circulation is different to that of the adult
  2. the placenta (not the lung) is the site of gas exchange
  3. foetal adaptations must be reversed at birth
45
Q

Why is oxygenated blood entering into the right ventricle of a foetus?

A

Oxygenated blood is coming from the umbilical veins

46
Q

What 2 structures are present in foetal circulation that allow blood to bypass the lungs?

A
  1. ductus arteriosus

2. foramen ovale

47
Q

How is neonatal wellbeing assessed?

A

APGAR score

Appearance

Pulse

Grimace

Activity

Respiration

48
Q

How does APGAR scoring work?

A

Each category is measured at 1. 5 and 10 minutes

Two points are awarded for each category

49
Q

What % of deliveries are classed as preterm?

What determines whether a baby is preterm?

A

10% of pregnancies are preterm

Preterm pregnancies mean birth occurs before 37 weeks

50
Q

What are the negative consequences of preterm births?

A

Higher risk of mortality and morbidity

51
Q

How many babies are born preterm each year?

A

60,000 babies per year

52
Q

What are the common morbidities affecting preterm births?

A
  1. respiratory distress syndrome - O2 dependence
  2. intraventricular haemorrhage - cerebral palsy
  3. necrotising enterocolitis - malabsorption
  4. retinopathy - blindness
53
Q

How can the risk of preterm birth morbidities be reduced?

A
  1. corticosteroids
  2. ventilation
  3. artificial surfactant
  4. magnesium sulphate (to prevent cerebral palsy)
54
Q

What are the underlying reasons for why preterm births occur?

A
  1. uterine capacity
  2. cervical weakness
  3. placental abruption (comes away from uterine wall too early)
  4. local or systemic infections
55
Q

How can bacteria travel to affect the foetus?

A

it will travel up the vagina and through the cervix

It affects the chorion and amniotic fluid leading to chorioamnionitis

56
Q

What is a septate uterus?

How does it affect pregnancy?

A

There is a septum in the centre of the uterus

This leads to a reduced capacity of the uterus that cannot withstand a full-term pregnancy

57
Q

How can the shortened cervix be identified on ultrasound?

A

it has an hourglass shape

This is due to membranes bulging from the cervix into the vagina

58
Q

What is meant by birth asphyxia?

A

The baby is not getting enough oxygen during birth

59
Q

With each contraction of labour, what happens to blood flow?

A
  1. compression of myometrial arteries

2. this leads to cessation of flow to the placental bed

60
Q

What is the result of blood flow cessation to the placental bed during birth?

A
  1. lack of gas exchange
  2. relative foetal hypoxia during contraction
  3. anaerobic metabolism in baby
  4. gradual lactic acidosis over time
61
Q

What are the consequences of birth asphyxia?

A
  1. lactic acidemia
  2. tissue acidosis
  3. hypoxic-ischaemic encephalopathy
  4. cerebral palsy
62
Q

When is fetal distress, leading to birth asphyxia, more likely?

A
  1. less reserve (low birth weight)
  2. long labour
  3. impaired placental function
63
Q

What is a placental abruption and what can it lead to?

A

Where the placenta comes away from the uterine wall earlier than it should

It can lead to preterm birth

64
Q

What happens to the mother and the baby during placental abruption?

A

The baby experiences distress due to lack of oxygen

The mother will bleed severely

65
Q

What are the management methods for birth asphyxia?

A
  1. foetal heart rate monitoring
  2. measurement of foetal scalp pH
  3. monitor ST segment changes in fECG
  4. expedite delivery by cesarean section
66
Q

Under what conditions does birth asphyxia have a good prognosis?

A

it umbilical cord pH > 7.00

AND

BE is better than -12 mmol/l

BS - Reproductive System (12 decks)

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