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!!!!! BRS YR2 !!!!! > Age + Dev - Placentation + Pregnancy > Flashcards

Age + Dev - Placentation + Pregnancy Flashcards

(94 cards)

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1
Q

How does the embryo gain nutrition and grow in the first trimester?

A

Histiotrophic

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2
Q

What is histiotrophic support?

A

Gaining nutrients from the breakdown of endometrial tissues and uterine gland secretions for growth and development

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3
Q

Give an example of histiotrophic growth in early foetal development.

A

Synctiotrophoblasts invading maternal endometrium - this breakdown of local tissues + maternal capillaries fuels some of the embryo’s development

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4
Q

What type of support does the embryo switch to at the start of the 2nd trimester?

A

Haemotrophic support

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5
Q

What haemotrophic support?

A

Deriving nutrient directly from the maternal blood

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6
Q

Why does embryo support switch from histiotrophic to haemotrophic?

A

Needs to switch to maintain the increasing rate of growth of the embryo from 1st trimester to 2nd

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7
Q

How is haemotrophic support achieved?

A

Achieved through a haemochorial-type placenta where maternal blood directly contacts the fatal membranes

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8
Q

What are trophoblastic lacunae?

A

→ Large spaces filled with maternal blood formed by breakdown of maternal capillaries + uterine glands
→ become intervillous spaces AKA maternal blood spaces

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9
Q

What are fetal membranes?

A

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

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10
Q

What are the 4 different fetal membranes?

A

→ Innermost = Amnion
→ Outermost = Chorion
→ Allantois
→ Yolk Sac or Umbilical Vesicle

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11
Q

What is the amnion?

A

→ Innermost fetal membrane
→ Arises from the Epiblast but doesn’t contribute to the fetal tissues
→ Forms a closed avascular sac with the developing embryo at one end
→ Begins to secret amniotic fluid around the 5th week to fill the amniotic sac

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12
Q

What is the chorion?

A

→ Outer fetal membrane
→ Firmed from yolk sac derivatives and the trophoblast
→ Highly vascularised
→ Gives rise to the chorionic Villi

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13
Q

What is the connecting stalk?

A

Links developing embryo unit to the chorion

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14
Q

What is the allantois?

A

→ Outgrowth of the yolk sac
→ Grows along the connecting stalk from embryo to chorion
→ Becomes coated in mesoderm + vascularises to form the umbilical chord

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15
Q

What is the amniotic sac?

A

→ Inner membrane = amnion
→ Outer membrane = chorion
→ Fluid filled sac formed by the production of amniotic fluid
→ Encapsulates and protects the foetus
→ Forces amnion into contact with the chorion

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16
Q

What are chorionic villi?

A

Cytotrophoblast forms finger-like projections through syncitiotrophoblast layer into maternal endometrium

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17
Q

What is the main function of chorionic villi?

A

Provide substantial surface area for exchange

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18
Q

What are the 3 phases of chorionic villi development?

A

→ Primary
→ Secondary
→ Tertiary

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19
Q

What is the primary phase of chorionic growth?

A

Outgrowth of the cytotrophoblast and branching of its extensions

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20
Q

What is the secondary phase of chorionic villi growth?

A

Growth of the fetal mesoderm into the primary villi

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21
Q

What is the tertiary phase of chorionic villi growth?

A

Growth of the umbilical artery + vein into the villus mesoderm, providing vascular use

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22
Q

What is the microstructure of the terminal chorionic villus?

A

→ Convoluted knots of vessels with vessel dilation
→ Slows blood flow enabling exchange between maternal and fetal blood
→ Whole structure coated with trophoblast

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23
Q

What are the difference in terminal villus microstructure in early pregnancy and late pregnancy?

A

Villi become much thinner, vessels move within the villi to leave less trophoblast separation between maternal blood and capillaries

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24
Q

What arteries does the blood supply to the endometrium consist of?

A

→ Uterine artery give rise to network of Arcuate arteries in the myometrium
→ Arcuate arteries branch into Radial arteries
→ Radial arteries further branch into Basal arteries in the endometrium
→ Basal arteries form Spiral arteries during the menstrual cycle endometrial thickening

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25
How do spiral arteries remodel to become the maternal blood supply during pregnancy?
→ Extra-villus trophoblasts (EVT) cells coating the villi invade down into the maternal spiral arteries, forming endo vascular EVT → Endothelium and smooth muscle is broken down - EVT coats the inside of vessels → Turns spiral artery into low pressure, high capacity conduit for maternal blood flow
26
What is the process of spiral artery remodelling in pregnancy called?
Conversion
27
How is oxygen exchanged across the placenta?
diffusional gradient (high maternal O2 tension, low O2 fatal tension
28
How is glucose exchanged across the placenta?
facilitated diffusion by transporters on maternal side `+ fetal trophoblast
29
How is water exchanged across the placenta?
→ placenta is main site of exchange, though some H2O crosses at the amnion-chorion border → majority is by diffusion, with some local hydrostatic gradients
30
How are electrolytes exchanged across the placenta?
large traffic of sodium + other electrolytes across the placenta - combo of diffusion + active energy-dependent co-transport
31
How is calcium exchanged across the placenta?
actively transported against a conc. gradient by magnesium ATPase calcium pump
32
How are amino acids exchanged across the placenta?
reduced maternal urea excretion + active transport of AAs to foetus
33
What are the maternal changes when the maternal-fetal oxygen exchange occurs`?
→ maternal cardiac output increase 30`% during first trimester (stroke volume & rate) → maternal peripheral resistance decreases up to 30% → maternal blood volume increases to 40% → pulmonary ventilation increases 40%
34
What are the fetal changes when the maternal-fetal oxygen exchange occurs`?
→ placenta consumes 40-60% glucose and oxygen supplied → fetal O2 tension is low → O2 content + saturation are similar to maternal blood → embryonic + fetal haemoglobins have a greater affinity for O2 than maternal haemoglobin's
35
Describe how the circulatory system matures from 1st trimester to 2nd trimester.
→ Placenta acts as site of gas exchange for fetus → Ventricles act in parallel rather than series → vascular shunts bypass pulmonary & hepatic circulation -> close at birth
36
Describe how the respiratory system matures from 1st trimester to 2nd trimester.
→ Primitive air sacs form in lungs around 20 weeks, vascularization from 28 weeks → Surfactant production begins around week 20, up-regulated towards term 2 → Fetus spends 1-4h/day making rapid respiratory movements during
37
Describe how the gastrointestinal system mature from 1st trimester to 2nd trimester.
→ Endocrine pancreas functional from start of 2T, insulin from mid-2T → Liver glycogen progressively deposited – accelerates towards term → Large amounts of amniotic fluid swallowed –debris and bile acids form meconium
38
Describe how the nervous system mature from 1st trimester to 2nd trimester.
→ Fetal movements begin late 1T, detectable by mother from ~14 weeks → Stress responses from 18 weeks, thalamus-cortex connections form by 24 weeks → Fetus does not show conscious wakefulness – mostly in slow-wave or REM sleep
39
How is feral organ maturation co-ordinated?
fetal corticosteroids
40
What is the purpose of labour?
→ Safe expulsion of the fetus at the correct time → Expulsion of the placenta and fetal membranes → Resolution/healing to permit future reproductive events
41
What are the 4 phases of pregnancy from conception to fertility restoration?
→ phase 1 : QUIESCENCE : prelude to parturition → phase 2 : ACTIVATION : preparation for labour → phase 3 : STIMULATION : processes of labour → phase 4 : INVOLUTION : parturient recovery
42
What are the characteristics of Phase 1?
→ between conception and initiation of parturition → contractile, unresponsiveness → cervical softening
43
What are the characteristics of phase 2?
→ between initiation of parturition and onset of labour → uterine preparedness for labour → cervical ripening
44
What are the characteristics of phase 3?
``` → between onset of labour and delivery of conceptus → uterine contraction → cervical dilation → fetal and placenta expulsion → involves 3 stages of labour ```
45
What are the characteristics of phase 4?
→ between delivery of conceptus and fertility restoration → uterine involution → cervical repair → breast feeding
46
What type of reaction does labour share the characteristics of? Why?
pro-inflammatory reaction → immune cell infiltration → inflammatory cytokine + prostaglandin secretion
47
What are the 3 stages of labour?
``` 1 = contractions start + cervix dilation 2 = delivery of fetus 3 = delivery of the placenta ```
48
What can the first stage be divided into?
→ latent phase | → active phase
49
What is involved in the latent part of the first stage?
slow dilation of the cervix to 2-3cm
50
What is involved in the active stage of the first stage?
rapid dilation of the cervix to 10cm
51
What is involved in the second stage of labour?
→ commences at full dilation of the cervix (10cm) | → maximal myometrial contractions
52
What is involved in the third stage?
→ expulsion of placenta + fatal membranes | → post-partum repair
53
How long is the first delivery typically?
8-18 hrs
54
How long are subsequent deliveries typically?
5-12 hrs
55
What is the role of the cervix?
retains fetus in uterus
56
What features does the cervix have in order to be able to complete its function?
→ High connective tissue content (Provides rigidity, Stretch resistant) → Bundles of collagen fibres embedded in a proteo-glycan matrix → Changes to collagen bundle structure underlie softening, but mechanism unclear
57
What are the 4 phases of cervix remodelling?
→ softening → ripening → dilation → post-partum repair
58
What is involved in the softening of the cervix?
→ begins in first trimester | → measurable changes in compliance but retains cervical competence
59
What is involved in the dilation of the cervix?
→ Increased hyaluronidase expression -> HA breakdown | → MMPs decrease collagen content
60
What is involved in the ripening of the cervix?
→ increased elasticity | çmonocyte infiltration and IL-6 and IL-8 secretion hylaluron deposition
61
What is involved in post-partum repair?
recovery of tissue integrity and competency
62
How does a fetus determine timing of parturition?
→ through changes in fetal HPA axis → corticosteroids-releasing hormone rise exponentially towards the end of pregnancy → decline in CRH binding protein levels so CRH bioavailability increases
63
What are the functions of CRH in labour?
→ promotes fetal ACTH and cortisol release → Increasing cortisol drives placental production of CRH = Positive feedback! → stimulates DHEAS production by the fetal adrenal cortex = substrate for estrogen production
64
What is the progesterone level throughout pregnancy? Explain.
high progesterone = uterine relaxation
65
How does the oestrogen to progesterone ratio change towards the end of the pregnancy?
→ serum E:P ratio shifts in favour of E → As term approaches, switch from PR-A isoforms (activating) to PR-B and PR-C (repressive) isoforms expressed in the uterus -> functional prog. withdrawal → Rise in Estrogen Receptor Alpha expression → Uterus becomes ‘blinded’ to progesterone action and sensitized to estrogen action → Control of these changes unclear but likely leads to local changes in E:P ratio in uterine tissues.
66
What type of hormone is oxytocin?
nonapeptide (9aa) hormone
67
Where is oxytocin produced?
→ utero-placental tissues | → pituitary
68
When does uterine oxytocin production increase?
sharply at the onset of labour
69
What is oxytocin expression driven by?
oestrogen levels
70
What is oxytocin release promoted by?
stretch receptors (Ferguson reflex)
71
What is the Ferguson Reflex?
neuroendocrine reflex in which the fetal distension of the cervix stimulates a series of neuroendocrine responses, leading to oxytocin production
72
What receptors respond to oxytocin in the uterus?
G-coupled oxytocin receptor (OTR / OXTR)
73
What inhibits the expression of OXTRs / OTRs pre-labour?
progesterone (keeps the uterus relaxed)
74
What increases OTR / OXTR expression?
rise in oestrogen
75
What are the functions of oxytocin during labour?
→ increases connectivity of myocytes in myometrium (syncytium) → destabilise membrane potentials to lower threshold for contraction → enhances liberation of intracellular Ca2+ ion stores
76
What are the key effectors of labour?
prostaglandins
77
What are the 3 primary prostaglandins synthesised during labour?
→ PGE2 → PGF2-alpha → PGI2
78
What drives prostaglandin action in uterus?
rising oestrogen levels
79
In what 2 ways does oestrogen drive prostaglandin action in the uterus?
→ rising oestrogen activates phospholipase A2 enzyme = generating more arachidonic acid for PG synthesis → oestrogen stimulation of oxytocin receptor expression promotes prostaglandin release
80
What are the functions of PGE2?
→ cervi xremodelling | → promotes leukocyte infiltration into the cervix, IL-8 release + collagen bundle re-modelling
81
What are the functions of PGF2-alpha?
→ myometrial contractions | → destabilises membrane potentials + promotes connectivity of myocytes (w/ Oxytocin)
82
What are the functions of PGI2?
→ promotes myometrium smooth muscle relaxation | → relaxation of lower uterine segments
83
What are some other factors involved in cervix remodelling?
→ peptide hormone RELAXIN | → NO - nitric oxide
84
What do myometrial muscle cells form?
synctium (multi-nucleate cell formed from unicellular cells) with extensive gap junctions
85
Where do contractions of the myometrium start? Where do they spread?
→ fundus | → spread down upper segment
86
How are the myometrial muscle contractions described?
brachystatic | → fibres don't return to full length on relaxation
87
What do the brachystatic contractions of the myometrium form?
lower segment + cervix get pulled up = forms birth canal
88
What happens to the uterus after fetal delivery?
rapid shrinkage of uterus
89
What does uterus shrinkage cause?
→ area of contact of placenta with endometrium shrinks | → folding of fetal membranes (they peel off the endometrium)
90
What does the clamping of the umbilical cord lead to?
→ stops fetal blood flow to placenta | → causes villi colapse
91
What forms between the decidua and placenta after fetal delivery?
hematoma
92
How are the placenta + fetal tissues expelled from the uterus after fetal delivery?
→ uterus rapidly shrinks after delivery → area of contact between placenta + endometrium shrinks → fetal membranes begin to fold + peel off the endometrium → hematoma forms between placenta + decidua → contractions expel placenta + fetal tissues
93
Does the uterus contract or relax after delivery? Why?
→ contracted | → to facilitate uterine vessel thrombosis
94
How is the non-pregnant state of the uterus restored?
→ uterine involution + cervix repair → shielding uterus from commensurate bacteria → restore endometrial cyclicity in response to hormones

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