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BRS DEVELOPMENT AND AGEING > 1a Pregnancy, Parturition and Late Fetal Development > Flashcards

1a Pregnancy, Parturition and Late Fetal Development Flashcards

1
Q

During the first trimester, why is embryo-fetal development relatively slow?

A

Because the embryo is dependent on histiotrophic nutrition

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2
Q

what is histiotrophic nutrition?

A

The derivation of nutrients from the breakdown of surrounding tissues

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3
Q

How does the syncytioblast invading the endometrium provide histiotrophic nutrition?

A

Invaded and breaks down local tissues, and used products to fuel development of the embryo

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4
Q

When does the switch from histiotrophic to haemotrophic nutrition occur?

A

At the start of the second trimester

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5
Q

How is haemotrophic nutrition achieved?

A

through haemochorial - type placentas where the materal blood is directly in contact with the fetal membranes

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6
Q

When is the haemochorial-type placenta activated?

A

Around 12th week of gestation

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7
Q

What is the amnion derived from?

A

Epiblast

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8
Q

What does the amniotic cavity become?

A

The amniotic sac

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9
Q

What does the amniotic sac do?

A

surrounds and cushions fetus during 2nd and 3rd trimester

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10
Q

What is the chorion?

A

The second fetal membrane which surrounds the whole conceptus unit

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11
Q

What is the connecting stalk?

A

Links the developing embryo unit to the chorion

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12
Q

What are the trophoblastic lacunae?

A

Large spaces filled with maternal blood formed by the breakdown of maternal capillaries and uterine glands

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13
Q

What are the intervillous spaces that are formed when maternal capillaries break down?

A

Maternal blood spaces

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14
Q

What are fetal membranes?

A

Extra-embryonic tissues that form a tough but flexible sac that encapsulates the fetus and forms the basis of the maternal-fetus interface

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15
Q

What is the amnion?

A

The inner fetal membrane which arises from the epiblast, and forms an enclosed, avascular sac with the developing embryo at one end

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16
Q

When does the amnion start to secrete amniotic fluid?

A

From 5th week - forms a fluid filled sac that encapsulates and protects the fetus

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17
Q

Which fetal membrane is highly vascularised?

A

Chorion

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18
Q

What is the chorionic villi?

A

Outgrowths of the cytotrophoblast from the chorion that forms the basis of the fetal side of the placenta

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19
Q

How does the amniotic sac form?

A

Expansion of the amniotic sac by fluid accumulation forces the amnion into contact with the chorion, which fuse forming the amniotic sac

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20
Q

What is the allantois?

A

An outgrowth of the yolk sac which grows along the connecting stalk from embryo to chorion

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21
Q

How does the umbilical cord form?

A

Coated in mesoderm and vascularises to form the umbilical cord

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22
Q

What is found on the inside and outside of the amniotic sac?

A

Amnion on the inside, chorion on the outside

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23
Q

Where do the primary chorionic villi project to?

A

they project through the syncitiotrophoblast layer into the maternal endometrium

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24
Q

What happens in the primary stage of chorionic villi development?

A

outgrowth of the cytotrophoblast and branching of these extensions

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25
Q

What happens in the secondary stage of chorionic villi formation?

A

Growth of the fetal mesoderm into the primary villi

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26
Q

What happens in the tertiary phase of chorionic villi development?

A

Growth of the umbilical artery and umbilical vein into the villus mesoderm providing vasculature

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27
Q

Describe the microstructure of the terminal villus?

A

A convoluted knot of vessels and vessel dilation

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28
Q

Why is the terminal villus knotted?

A

Slows the blood flow, allowing exchange of material between maternal and fetal blood

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29
Q

What coats the entire terminal villus structure?

A

the trophoblast

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30
Q

What is the approx diameter of the terminal villus during early pregnancy?

A

150-200 micrometers in diameter

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31
Q

What is the approx diameter of the terminal villus during late pregnancy?

A

the villli thin to 40 micrometers

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32
Q

What happens to the thickness of the trophoblast that surrounds the terminal villi as you move from early to late pregnancy?

A

10 micrometers to 1-2 micrometers

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33
Q

What forms from the branching of uterine arteries?

A

Arcuate arteries

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34
Q

What branches from the arcuate arteries?

A

Radial arteries

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35
Q

What do the radial arteries branch to form?

A

Basal arteries

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36
Q

During menstrual cycle endometrial thickening what do the basal arteries form?

A

Spiral Arteries

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37
Q

What happens to the spiral arteries if implantation does not occur?

A

The spiral arteries regress

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38
Q

What do the spiral arteries do?

A

provide the maternal blood to the endometrium

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39
Q

How does the endovascular EVT form?

A

The EVT cells (Extra-villus trophoblast) cells coating the villi invade down into the maternal spiral arteries

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40
Q

What is meant by the process of conversion?

A

When the spiral artery is converted into a low pressure, high capacity conduit maternal blood flow

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41
Q

How is glucose transported across the placenta?

A

Facilitated diffusion by transporters on maternal side and fetal trophoblast cells

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42
Q

How is water transported across the placenta?

A

Placenta is the main site for exchange, through some crosses the amnion-chorion

Majority is through diffusion, though some local hydrostatic gradients

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43
Q

How are electrolytes transported across the placenta?

A

Large traffic of sodium and other electrolytes across the placenta - through a combination of diffusion and active energy dependant co-transport

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44
Q

How is calcium transported across the placenta membrane?

A

Actively transported against a concentration gradient by magnesium ATPase calcium pump

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45
Q

How are amino acids transported across the placenta?

A

Reduced maternal urea excretion and active transport of amino acids to fetus

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46
Q

How does maternal cardiac output change during the first trimester?

A

Increases by 30% during first trimester (through increases in stroke volume and rate)

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47
Q

How does maternal peripheral resistance change through pregnancy?

A

Decreases up to 30%

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48
Q

How does maternal blood volume change near term?

A

blood volume increases by 40% near term

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49
Q

How does maternal pulmonary ventilation change during pregnancy?

A

Increases

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50
Q

How much glucose and oxygen supplied by the mother does the placenta consume?

A

40-60%

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51
Q

How is the affinity for O2 different between maternal and fetal haemoglobin?

A

HbF has a higher affinity for Oxygen than Maternal Hb

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52
Q

Why does the placenta consume so much glucose and oxygen?

A

it is a highy metabolic tissue

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53
Q

What process reduces maternal vessel pressure and increases capacity?

A

Spiral Artery remodelling

54
Q

What is the role of the placenta?

A

A site of gas exchange for the foetus

55
Q

Vascular shunts bypass pulmonary and hepatic circulation. What effect does this have?

A

Allows the placenta to drive oxygenated blood around the body

56
Q

At what point do primitive air sacs form in the lungs?

A

Around 20 weeks

57
Q

When does surfactant production begin?

A

Around week 20

58
Q

Why does the foetus spend a large proportion of their day making rapid respiratory movements?

A

It is practice for breathing when it comes out the womb

59
Q

What is the meconium?

A

The first stool which is delivered after birth

60
Q

What forms the meconium?

A

The large amount of amniotic fluid which the foetus swallows - contains debris and bile acids which form the meconium

61
Q

When do thalamus-cortex connections form in the foetus?

A

By 24 weeks

62
Q

When can fetal movements be detected?

A

Approx 14 weeks

63
Q

What increases towards the end of pregnancy that is responsible for the organ maturation and changes seen?

A

Corticosteroids

64
Q

What is the definition of labour?

A

The safe expulsion of the foetus at the correct time, including the placenta and the fetal membranes

65
Q

What is important to ensure can occur after labour?

A

The resolution and healing of the uterus to permit future reproductive events

66
Q

What two events that occur during labour are characteristic of a pro-inflammatory reaction?

A

Immune cell infiltration

Inflammatory cytokine and prostaglandin secretion

67
Q

What does prostaglandins do during labour?

A

Orchestrate the timing and sequence of the events of labour

68
Q

What are the three stages of labour?

A
  1. Contractions start and cervical dilation
  2. Delivery of fetus
  3. Delivery of the placenta
69
Q

What are the two stages of the first labour stage?

A

The latent phase and active phase

70
Q

What occurs during the latent phase?

A

Slow dilation of the cervix to 2-3 cm

71
Q

What occurs during the active phase of labour?

A

Rapid dilation of the cervix to 10cm

72
Q

When does the second stage of labour commence?

A

When the cervix is fully dilated to 10cm

73
Q

What occurs during the second stage of labour?

A

Maximal myometrial contractions - intense and frequent

74
Q

What occurs during the third stage of labour?

A

Expulsion of the placenta and fetal membranes

75
Q

How does the time the mother is in labour change between her first and second pregnancy?

A

Decreases

8-18 h to 5-12 h

76
Q

What does the high connective tissue content of the cervix allow?

A

Provides rigidity and stretch resistance, both help keep the cervix closed

77
Q

Describe the tissue structure of the cervix?

A

Bundles of collagen fibres embedded in a proteo-glycan matrix

78
Q

What changes occur to the cervix near delivery time?

A

Changes to the collagen bundles underlie the softening of the cervis

79
Q

What are the three processes the cervix undergoes?

A

Softening
Ripening
Dilation

80
Q

When does softening of the cervis occur?

A

Begins in the first trimester

81
Q

Describe the process of spiral arery remodelling?

A
  1. Extravillus throphoblast cells are shed off he chorionic villi
  2. They invade fown the spiral arteries, displacing the maternal endothelium by forming a new one, and thus remodelling the spiral arteries
  3. This process increases the diameter if the blood vessels and makes them not spiral, lowering the pressure and increases blood flow to the placenta
82
Q

When does ripening of the cervix occur?

A

Weeks. days before birth

83
Q

What occurs during ripening of the cervix?

A

Monocyte infiltration
IL-6 and IL-8 Secretion
Hyaluron deposition

84
Q

What acts to decrease collagen content during dilation of the cervix?

A

Matrix metalloproteinases

85
Q

What occurs during the dilation phase of cervical remodelling?

A

Increase hyaluronidase expression, which leads to HA breakdown

86
Q

Why is post partum repair of the cervix so important?

A

It ensures that the mother is able to have another pregnancy - recovery of tissue integrity and competency

87
Q

Which two immune cells are present in larger quantities during labour?

A

Macrophages and neutrophils

88
Q

How is labour initiated?

A

The fetus determines the timing of parturition through changes in the fetal HPA axis

89
Q

Levels of what hormone rise exponentially towards the end of pregnancy?

A

Corticotrophin-Releasing Hormone (CRH)

90
Q

How do CRH levels increase towards the end of pregnancy?

A

There is a decline in CRH binding protein so this means the amount of free, circulating CRH that is bioavailable and therefore free to circulate increases

91
Q

What functions do CRH have in labour?

A

Promote fetal ACTH and cortisol release

92
Q

What affect does increasing cortisol production have on the placenta?

A

Drives placental production of CRH, resulting in a positive feedback look, as CRH promotes fetal cortisol production

93
Q

What affect does cortisol have on the fetal adrenal cortex?

A

Stimulates DHEAS production - this is a substrate for oestrogen production

94
Q

Why is it important that progesterone remains high throughout pregnancy?

A

High progesterone maintains uterine relaxation

95
Q

Describe the shift in progesterone receptor subtypes which occurs in the uterus as term approaches? And what effect does this have

A

There is a switch from PR-A isoform (activating) to PR-B and PR-C (repressive) isoforms, which leads to functional progesterone withdrawal

PR = Progesterone receptor

Despite the levels of progesterone still being high, this switch in receptor type blinds the uterus to the actions of progestone - meaning the endometrium is able to start to degrade and release the baby etc etc

96
Q

What does functional progesterone withdrawal involve?

A

The blinding of the uterus to progesterone action and sensitization to eostrogen action

97
Q

What affect does functional progesterone withdrawal have on the overall estrogen:progesterone radio?

A

MAY shift in favour of oestrogen, increase ratio - this is not 100% clear

98
Q

There is an increase in the expression of what receptor during pregnancy?

A

Estrogen Receptor Alpha

99
Q

Where is nonapeptide hormone synthesized?

A

Mainly in the utero-placental tissues and the pituitary

100
Q

How does uterine oxytocin production change towards the onset of labour?

A

it increases sharlpy

101
Q

What drives the increase in uterine oxytocin production?

A

Increase in oestrogen levels

102
Q

What is meant by the Ferguson reflex?

A

the fetal distension of the cervix stimulates a series of neuroendocrine responses, leading to oxytocin production.

103
Q

What affect does a rise in oestrogen have on uterine OXTR?

A

Oestrogen promotes a large increase in uterine OXTR

104
Q

What are the functions of Oxytocin to enable labour?

A
  1. Increases connectivity of myocytes by promoting the function of gap junctions
  2. Destabilise membrane potentials to lower the threshold needed for contraction
  3. Enhances the liberation of intracellular Ca2+ ion stores
105
Q

What are the three primary prostaglandins that are synthesized during labour

A

PGE2, PGF2Alpha and PGI2

106
Q

How does rising oestrogen drive prostaglandin action?

A

Activates phospholipase A2 enzyme, which generates more arachidonic acid for PG synthesis

Stimulation of oxytocin receptor expression prmotoes PG release

107
Q

what affect does PGE2 have?

A

Promotes leukocyte infiltration into the cervix, collagen bundle remodelling and IL-8 release which all contribute to cervix remodelling

108
Q

What affect does PGF2alpha have on labour?

A

Promotes myometrial contractions alongside oxytocin by destailising membrane potentials and promoting connectivity of myocytes

109
Q

What affect does PGI2 have?

A

Promotes myometrial smooth muscle relaxation and relaxation of lower uterine segment

110
Q

Why is the relaxation of lower uterine segments so important during labour?

A

Allows blood flow to return to the uterus and placenta to ensure there is blood flow to the foetus

111
Q

The levels of which two peptide hormones increase sharply towards the end of pregnancy?

A

Relaxin and Nitric oxide

112
Q

what stimulates the placenta to make prostaglandins?

A

Oxytocin

113
Q

Where do myometrial contractions originate?

A

The fundus

114
Q

What is meant by brachystatic contractions, as shown by the myometrial contractions?

A

The muscle fibres do not return to full length apon relaxation

115
Q

How does the birth canal form?

A

The brachystatic contractions of the myometrium causes the lower segment and cervix to be pulled up, forming the birth canal

116
Q

Which segment of the uterus contributes to contraction?

A

The upper segment

117
Q

At what stage does the head of the baby engage with the fetal space?

A

34-38 weeks

118
Q

What is meant by flexion of the fetal head?

A

When pressure on the fetus causes the chin to press up against the chest

119
Q

Which part of the baby is expelled first during birth?

A

The head after the cervix dilates

120
Q

What is birthed after the head of the fetus?

A

The shoulders (upper shoulder first) followed by the torso

121
Q

What affect does uterine shrinking have on the fetal membranes?

A

Causes them to fold and peel away from the endometrium

122
Q

What affect does clamping the umbilical cord at birth have?

A

Stops fetal blood flow to the placenta, causing the villi to collapse

123
Q

What effect does the collapse of the villi have

A

Causes a hematoma formation between the decidua and placenta

124
Q

Contractions of the uterus expell what?

A

The baby, placenta and fetal tissues

125
Q

Why does the uterus remain contracted after delivery?

A

To facilitate uterine vessel thrombosis (interuterine bleeding)

126
Q

What occurs to repair non-pregnant state?

A

Uterine involution and cervix repair

127
Q

What does uterine involution and cervical repair involve?

A

Sheilding uterus from commensural bacteria and restoration of endometrial cyclicity in response to hormones

128
Q

What is endometrial cyclicity?

A

The endometrium undergoes cyclic changes each month, under the overall control of fluctuating levels of estrogen and progesterone. This hormone dependent endometrial remodelling is a continuum of structural and functional changes that make up the menstrual cycle.

129
Q

Describe the hormone changes which occur towards the end of term?

A
  1. There is a switch in progesterone receptor from PA-A isoforms to PR-B and PR-C isoforms which are repressive
  2. This essentially blinds the uterus to the actions of progesterone despite the levels being high
  3. There is also an increase in estrogen receptors which allows the uterus to become sensitized to the estrogen
130
Q

Describe the integrated hypothesis for the regulation of labour?

A
  1. Fetal production of CRH increases
  2. This trigger the Fetal adrenal gland to increase Cortisol production
  3. This fetal cortisol then enters into the placenta and increases the production of maternal CRH
  4. The cortisol also stimulates the production of placental DHEAS
  5. This is is then converted into Oestrogen, casing oestrogen levels to rise
  6. Once oestrogen levels rise, this causes the sensitivity of the OTXR in the uterus to increase = contractions
  7. Also, the rising oestrogen causes an increase in the fetal and maternal production of Oxytocin - leading to vigorous contractions and prostaglandin synthesis

BRS DEVELOPMENT AND AGEING (6 decks)

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