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BRS D&A > Pregnancy, Parturition and Late Foetal Development > Flashcards

Pregnancy, Parturition and Late Foetal Development Flashcards

1
Q

Embryo-foetal growth during the first trimester is relatively limited, what type of nutrition is the early embryo dependent on?

A

histiotrophic nutrition

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2
Q

What is histiotrophic nutrition?

A

reliant on uterine gland secretions and breakdown of endometrial tissues

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3
Q

What type of support is embryo-foetal growth dependent on at the start of the 2nd trimester/ what type of support does it switch to?

A

Haemotrophic

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4
Q

How is the switch to haemotrophic nutrition achieved?

A

it is achieved in humans through a haemochorial-type placenta where maternal blood directly contacts the foetal membranes

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5
Q

What is the connecting stalk/ what does it do?

A

Connects the embryo unit to the chorion

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6
Q

What are trophoblastic lacunae?

A

Large spaces filled with maternal blood formed by breakdown of maternal capillaries and uterine glands
Become intervillous spaces aka maternal blood spaces

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7
Q

What is the amnion (in terms of foetal membranes), +what does it arise from, +what does it secrete?

A

The inner foetal membrane
Arises from the epiblast (but does not contribute to the foetal tissues)
Begins to secrete amniotic fluid from 5th week- forms fluid filled sac

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8
Q

Describe the amniotic sac.

A

closed, avascular sac, with the developing embryo at one end

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9
Q

Why is the amniotic sac important?

A

encapsulates and protects the foetus

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10
Q

What is the chorion, +what does it arise from (2), and what does it give rise to?

A

the outer foetal membrane
Formed from yolk sac derivatives and the trophoblast
Highly vascularised

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11
Q

What gives rise to chorionic villi?

A

Outgrowth of cytotrophoblasts from the chorion that form the basis of the foetal side of the placenta

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12
Q

What is the allantois/ what is it formed from, +what structure does it form?

A

Outgrowth of the yolk sac
Grows along the connecting stalk from embryo to chorion

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13
Q

How does the allantois form the umbilical cord?

A

Becomes coated in mesoderm and vascularises to form the umbilical cord

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14
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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15
Q

What are the 2 layers of the amniotic sac?

A

amnion on the inside, and chorion on the outside

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16
Q

Why are chorionic villi important?

A

they provide substantial SA for exchange of gases and nutrients

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17
Q

Describe the primary phase of chorionic foetal development.

A

Cytotrophoblasts form finger-like projections through syncitiotrophoblast layer, into maternal endometrium
Outgrowth of cytotrophoblast cells from the chorion

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18
Q

Describe the secondary phase of chorionic foetal development.

A

Growth of the foetal mesoderm into the primary villi

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19
Q

Describe the tertiary phase of chorionic foetal development.

A

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

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20
Q

Terminal villus microstructure; what does the convoluted knot of vessels and vessel dilation do?

A

slows blood flow enabling exchange between maternal and foetal blood

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21
Q

Briefly outline the branching of the maternal blood supply to the endometrium.

A

Uterine artery–> arcuate arteries–> radial arteries–> basal arteries–> spiral arteries

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22
Q

What do spiral arteries do?

A

Provide maternal blood supply to the endometrium

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23
Q

What do extra-villus trophoblast (EVT) cells do? (N.B. these cells come from chorionic villi)

A

cells coating the villi invade down into the spiral arteries and then form endovascular EVT

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24
Q

What is conversion?

A

Transition from spiral arteries to non-spiral arteries.
Turns the spiral artery into a low pressure, high capacity conduit for maternal blood flow.
Endothelium and smooth muscle is broken down- EVT coats inside of vessels.

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25
Describe placental structure diagram.
26
How is oxygen exchanges across the placenta?
diffusion gradient (simple diffusion)
27
How is glucose exchanges across the placenta?
facilitated diffusion
28
How is water exchanges across the placenta?
diffusion and hydrostatic gradients placenta is the main site for exchange of water
29
How are electrolytes exchanges across the placenta?
'diffusion' and 'active energy-dependent co-transport' across the placenta
30
How is calcium exchanges across the placenta?
actively transported against a concentration gradient by magnesium ATPase calcium pump
31
How are amino acids exchanges across the placenta? And how does the mother economise AA in pregnancy?
active transport of AA to foetus economise by less maternal urea excretion
32
What 4 changes occur in the maternal circulatory system?
Maternal Cardiac output increases 30% during first trimester (stroke vol and rate) Maternal peripheral resistance decreases up to 30% Maternal blood volume increases to 40% (near term (20-30% erythrocytes, 30-60% plasma) Pulmonary ventilation increases 40%
33
Why is the O2 content and saturation of foetal blood similar to maternal blood, even though foetal O2 tension is low? (what major difference does foetal Hb have to maternal Hb)
Embryonic and foetal haemoglobin: greater affinity for O2 than maternal Placenta consumes 40-60% glucose and O2 supplied by mother
34
What is the site for gas exchange for the foetus?
placenta
35
How does foetal circulation differ from neonatal (newborn) circulation?
ventricles act in parallel rather than in series (series is neonatal)
36
How is the parallel circulation possible?
by vascular shunts which bypass pulmonary and hepatic circulation, these shunts close at birth to give rise to normal pulmonary and hepatic circulation
37
What occurs in the lungs around week 28?
lung vascularises
38
What occurs in the lungs around week 20?
primitive air sacs form surfactant production - foetus spends 1-4h/day making respiratory movements during REM
39
At which point is the endocrine pancreas functional, and at which point does insulin secretion occur?
starts of 2nd trimester mid 2nd trimester
40
Which carbohydrate is progressively deposited towards the time of delivery?
glycogen
41
the early foetus swallows large amounts of amniotic fluid, debris from this fluid along with bile acids form the first stool of the foetus, delivered just after birth, what is the name of this stool?
meconium
42
At which point/ week does the foetus start to determine movement, and at which point/ week is movement detectable by mother?
late 1st trimester 14 weeks
43
At which point does the foetus start to respond to stress, and at which point do thalamus-cortex connections form?
18 weeks 24 weeks
44
Does the foetus show conscious wakefulness, Y/n?
No
45
What type of sleep is it mostly in?
slow-wave or REM sleep
46
Which hormone sub-class is organ maturation coordinated by?
Foetal corticosteroids
47
What are the 3 main aims of labour?
Safe expulsion of foetus at the correct time Expulsion of placenta and foetal membranes Resolution/ healing to permit future reproductive events
48
What reaction type does labour have the characteristics of and why?
pro-inflammatory reaction immune cell infiltration inflammatory cytokine secretion Prostaglandin secretion
49
Describe the first stage of labour.
Contractions start, cervix dilation occurs
50
Which 2 sub stages can cervix dilation be split into?
Latent phase=> slow dilation of the cervix 2-3cm Active phase=> rapid dilation of the cervix to 10cm
51
What is the role of the cervix in pregnancy?
a critical role in retaining the foetus in uterus
52
What property does the cervix have to fulfil its role?
High connective tissue content (bundles of collagen fibres embedded in a proteoglycan matrix) which is... - providing rigidity - stretch resistant
53
What change underlies softening of the cervix?
Changes to the collagen bundle structure
54
What are the 4 stages of cervix remodelling?
Softening Ripening Dilation Post-partum repair
55
What occurs during softening?
Measurable changes in compliance (stretch) but retains cervical competence (still able to keep foetus inside) It occurs in first trimester
56
What occurs during ripening?
Monocyte infiltration IL-6 and IL-8 secretion Hyaluronan deposition Occurs weeks and days before birth
57
What occurs during dilation?
Increased hyaluronidase expression, which breaks down hyaluronan Increased elasticity by matrix metalloproteinases decrease collagen content
58
What occurs during post-partum repair?
Recovery of tissue integrity and competency
59
Describe the second stage of labour.
Delivery of the foetus Myometrial contractions and foetal expulsion
60
What do myometrial muscle cells connect to form?
a syncytium (extensive gap junctions, allowing muscle contraction to be coordinated)
61
Where do contractions start from and where do they spread?
start from the fundus, spread down upper segment
62
What can myometrial muscle contractions be described as?
Brachystatic meaning that fibres do not return to a fully relaxed state and retain some shortening
63
What does myometrial contraction cause?
causes lower segment and cervix to be pulled up forming birth canal
64
Describe foetal expulsion.
pressure on foetus causes chin to press against chest baby belly to mother's spine head first shoulders delivered sequentially (followed by torso)
65
Describe the third stage of labour.
Delivery of the placenta and post-partum repair
66
What happens to the size of the uterus at this stage?
Rapid shrinkage of the uterus after foetal delivery
67
What effect does this have on the area of contact between the placenta and the uterine endometrium?
reduces/ shrink
68
What does clamping of the umbilical cord cuase?
Stop foetal blood flow to placenta, so the chorionic villi collapse
69
where does hematoma formation occur between?
decidua and placenta
70
What do ongoing myometrial contractions cause?
expel placenta and foetal tissues
71
Why does the uterus remain in a contracted state after placental delivery?
to facilitate uterine vessel thrombosis
72
The uterus undergoes uterine involution and the cervix undergoes repair to restore a non-pregnant state, why is this important?
Shielding uterus from commensal bacteria Restore endometrial cyclicty in response to hormones
73
Corticotrophin releasing hormone (CRH) levels rise exponentially towards the end of pregnancy, what does an increase in foetal CRH release cause?
1. promotes foetal ACTH and cortisol release 2. Stimulates DHEAS production by the foetal adrenal cortex, DHEAS is a substrate for oestrogen production
74
Describe the foetal-placental CRH and cortisol positive feedback.
increased foetal CRH production → increased foetal adrenal cortisol (this travels to the placenta)→ increases placental CRH production → Placental CRH stimulates more foetal CRH release
75
Why are high progesterone levels important to have throughout pregnancy?
maintains uterine (myometrial) relaxation
76
How might the oestrogen: progesterone ration shift during labour?
increases
77
The uterus becomes non-responsive to progesterone action and sensitised to oestrogen action, describe 2 ways which this occurs?
1. Functional progesterone withdrawal 2. Increased oestrogen receptor alpha expression
78
What is functional progesterone withdrawal?
switch from PR-A isoforms (activating) to PR-B and PR-C (repressive) isoforms expressed in uterus Pr= progesterone receptor
79
Explain the Ferguson reflex.
stretch receptors in vagina and cervix trigger oxytocin release from the posterior pituitary
80
How does oxytocin production change at the onset of labour?
Uterine oxytocin production increases sharply
81
What is oxytocin mainly secreted by?
utero-placental tissues maternal pituitary
82
What is increased oxytocin production driven by?
increased (placental) oestrogen levels
83
Stretch receptors in the cervix and vagina triggers release of oxytocin from the posterior pituitary in a neuroendocrine reflex, what is the name of this reflex?
Ferguson reflex
84
What receptor does oxytocin signal through?
G-coupled oxytocin receptor (OTR/ OXTR)
85
During pre-labour, what effect does progesterone have on the OXTR expression?
Inhibits OXTR expression, which allows the uterus to remain in a relaxed state (so no contractions)
86
What effect does increasing oestrogen have on OXTR expression?
increase it
87
What are the 3 main functions of oxytocin during pregnancy?
Increases connectivity of myocytes in myometrium Destabilises membrane potentials to lower threshold for contraction Enhances liberation of intracellular Ca2+ ion stores
88
What are the 3 main prostaglandins (PGs) synthesised during labour?
PGE2 PGF2 PGI2
89
What is the main role of PGE2?
Cervix re-modelling By promoting leukocyte infiltration into the cervix, IL-8 release and collagen bundle re-modelling (other factors: peptide hormone relaxin and nitric oxide (NO) implicated in cervix re-modelling)
90
What is the main role of PGF2?
Myometrial contractions By destabilising membrane potentials and promotes connectivity of myocytes (with oxytocin)
91
What is the main role of PGI2?
Myometrial relaxation
92
How does increase in oestrogen levels drive prostaglandin action?
1. Increasing oestrogen activates phospholipase A2 enzyme, which generates more arachidonic acid for PG synthesis 2. Increases oxytocin receptor expression which promotes PG release
93
Diagram for integrated hypothesis for the regulation of labour.

BRS D&A (8 decks)

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