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BRS Ageing and Development > placentation and parturition > Flashcards

placentation and parturition Flashcards

1
Q

What form of embryonic nutrition leads to the breakdown of maternal endometrial
capillaries to form trophoblastic lacunae?

A

histiotrophic

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2
Q

haemotrophic nutrition

A

start of 2nd trimester

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3
Q

what type of placenta do humans have?

A

haemochorial

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4
Q

histiotrophic

A

Histotroph is the nutritional material accumulated in spaces between the maternal and fetal tissues, derived from the maternal endometrium and the uterine glands. This nutritional material is absorbed by phagocytosis initially by blastocyst trophectoderm and then by trophoblast of the placenta

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5
Q

hemotrophic nutrition

A

hemotrophic nutrition is the exchange of blood-borne materials between the maternal and fetal circulations

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6
Q

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 chorion?

A

The chorion is a double-layered membrane formed by the trophoblast and the extra-embryonic mesoderm

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8
Q

what is the difference between the amnion and the chorion

A

The amnion is found on the innermost part of the placenta. It lines the amniotic cavity and holds the amniotic fluid and the developing embryo. … The chorion, on the other hand, is the outer membrane that surrounds the amnion

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9
Q

formation of amnion

A

ballon analogy
arises from epiblast
Forms a closed, avascular sac with the developing embryo at one end
Begins to secrete amniotic fluid from 5th week – forms a fluid filled sac that encapsulates and protects the fetus

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10
Q

chorion

A

formed from yolk sac derivatives
highly vascularised
gives rise to chorionic villi

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11
Q

what is the umbilical chord formed from?

A

allantois
outgrowths of yolk sac
connecting stalk from embryo to chorion
once coated in mesoderm and vascularised becomes umbilical chord

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12
Q

chorionic villus formation

A 
Cytotrophoblast forms
finger-like projections 
through 
syncitiotrophoblast layer
Into maternal
endometrium

only cytotrophoblasts have ability to proliferate

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13
Q

villus microstructure

A

convulated know of vessels
slow blood flow: enabling exchange
coated in trophoblast

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14
Q

what changes occur to terminal villus over pregnancy?

effect of these changes?

A

1 - thins out to 40um diameter (from 200)

2 - trophoblastic covering also thins to only 1-2um separation from maternal blood

enable a rapidly growing embryo in later stages which requires a lot more oxygen, blood flow, nutrients
distance of diffusion reduces

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15
Q

maternal blood supply

A

ovarian artery > arcuate> radial> basal> spiral

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16
Q

ovarian artery > _____> radial>_____>_______

A

ovarian artery > arcuate> radial> basal> spiral

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17
Q

_____ > arcuate>____> ___l> spiral

A

ovarian artery > arcuate> radial> basal> spiral

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18
Q

endovascular EVT formation

A

Extra-villus trophoblast (EVT) cells which coat villi invade down
the spiral arteries
form endovascular extra-villus trophoblast cells

this replaces maternal endothelium, smooth muscle

evt coats inside of the vessel

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19
Q

what is conversion?

A

maternal spiral arteries invaded by villus trophoblast, replaced by endovascular EVT
conduit for maternal blood flow

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20
Q

calcium exchange across placenta

A

Calcium: actively transported against a concentration gradient by magnesium ATPase calcium pump

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21
Q

maternal changes

A

Maternal blood volume increases to 40% (near term (20-30% erythrocytes, 30-60% plasma

cardiac output increased by 30%: stroke volume / rate

Pulmonary ventilation increases 40%

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22
Q

placenta/ fetus oxygen exchange

A

Placenta consumes 40-60% glucose and O2 supplied

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23
Q

why is the fetus able to consume 40-60% of oxygen?

this is a sickening fact!

A

fetal / embryonic haemoglobin has a higher affinity for o2 than maternal

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24
Q

what forms chorionic villus and what is its function?

A

invasion of chorionic cytrophoblast cells into maternal endometrium
surface for exchange

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25
Q

why does the fetus make rapid respiratory movements when it doesnt need to?

A

perhaps to practise breathing reflex

to aid diaphragm development

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26
Q

circulatory system

A

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

27
Q

Gastrointestinal

System

A

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 (1st poo lining baby’s intestines during pregnancy)

28
Q

nervous system

A

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

29
Q

resp system

A

Primitive air sacs form in lungs around 20 weeks, vascularization from 28 weeks
Surfactant production begins around week 20, upregulated towards term
Fetus spends 1-4h/day making rapid respiratory movements during REM sleep

30
Q

3 aims of labour?

A

Safe expulsion of the fetus at the correct time

Expulsion of the placenta and fetal membranes

Resolution/healing to permit future reproductive events

31
Q

role of prostaglandins during labour

A

Immune cell infiltration
Inflammatory cytokine and prostaglandin secretion

all aid in labour
which has characteristics of a pro - inflammatory reaction

32
Q

first stage of labour

A

contractions start

latent phase: slow dilation of cervis 2/3 cm

active phase - rapid dilation 10cm

33
Q

second stage

A

delivery of fetus

maximal myometrial contractions

34
Q

third stage

A

Explusion of placenta and fetal membranes

Post-partum repair

35
Q

cervix remodelling

A

Changes to collagen bundle structure underlie softening, but mechanism unclear

from rigid, stretch resistant to softening

Ripening : Monocyte infiltration and IL-6 and IL-8 secretion
Hylaluron deposition

Dilation : Increased hyaluronidase expression -> HA breakdown
MMPs decrease collagen content

post partum repair
recovery of tissue integrity and competency

36
Q

what is MMPs?

A

matrix mellano proteases

37
Q

Initiation of labour - how does it start?

A

fetus determines
as there are changes in the fetal HPA axis- CRH levels rise exponentially
decrease in CRH bidning protein levels so more bioavailable CRH

38
Q

what is CRH?

A

corticotrophin releasing hormone

39
Q

what is the role of CRH?

3 things it does

A

1) promotes fetal ACTH and cortisol release
2) drives placental prodcution of CRH - POSITIVE feedback loop
3) stimulates DHEAS production by fetal adrenal cortex

40
Q

what is a substrate for oestrogen production and is produced by the fetal adrenal cortex
this substrates production is stimulated by CRH

A 
DHEAS
 Dehydroepiandrosterone sulphate (DHEAS) is an androgen primarily produced by the adrenal cortex
41
Q

what maintains uterine relaxation throughout pregnancy?

A

HIGH progesterone

42
Q

describe functional progesterone withdrawal

A

term approaches
shift from activating signalling progesterone isoform A to progesterone B, C isoforms.
These are repressive isoforms expressed in uterus and cause the uterus to become blind to progesterone action
simultaneous rise in estrogen receptor alpha expression

43
Q

summarise progesterone withdrawal as term approaches

A

PR-A switch to PR-B, PR-C; from activating receptors to repressive receptors
suppression of alpha oestrogen receptor expression is also removed
Estrogen can then act to transform the myometrium to a contractile phenotype

44
Q

what is ferguson reflex?

A

The Ferguson reflex is a neuroendocrine reflex in which the fetal distension of the cervix stimulates a series of neuroendocrine responses, leading to oxytocin production

45
Q

what increases oxytocin production

A

Uterine oxytocin production increases sharply at onset of labour
Expression increase is driven by increase in estrogen levels.
Release promoted by stretch receptors -> Ferguson reflex

46
Q

what is the oxytocin signalling?

A

Signals through G-coupled oxytocin receptor (OTR / OXTR)

47
Q

what inhibits oxytocin signalling pre labour?

A

Pre-labour: progesterone inhibits OXTR expression -> uterus relaxed

48
Q

what promotes uterine OXTR expression?

A

Rise in estrogen promotes large increase in uterine OXTR expression

49
Q

3 functions of oxytocin

A

Increases connectivity of myocytes in myometrium (syncytium)
Destabilise membrane potentials to lower threshold for contraction
Enhances liberation of intracellular Ca2+ ion stores

50
Q

what is relevance of liberation of Ca2+ ion stores by oxytocin?

A

aids myometrial contraction

51
Q

Primary Prostaglandins synthesized during labour? are PGE2, PGF2alpha and PGI2

A

PGE2,
PGF2alpha
PGI2

52
Q

what drives prostaglandin action?

A

Rising estrogen levels

53
Q

2 ways

rising estrogen levels drives prostaglandin action?

A

. Rising estrogen activates phospholipase A2 enzyme, generating more arachidonic acid for PG synthesis
2. Estrogen stimulation of oxytocin receptor expression promotes PG release.

54
Q

action of PGE2

A

cervix re-modelling
IL8 release
collagen bundle re-modelling
leukocyte infiltration into cervix

55
Q

PGF2 alpha action

A

. destabalises membrane potentials

promotes connectivity of myocytes

56
Q

PGI2

A

myometrium

between contraction and relaxation allows for myometrial smooth muscle relaxation of lower uterine segment

57
Q

what factors implicated in cervix re-modelling other than prostaglandin

A

peptide hormone relaxin

nitric oxide

58
Q

what forms a syncytium

A

myometrial muscle cells - extensive gap junctions

contraction start at fondus

59
Q

what does brachystatic mean?
muscle contractions in fetal expulsions are like this
what does it do?

A

Muscle contractions are brachystatic –fibres do not return to full length on relaxation

This causes lower segment and cervix to be pulled up forming birth canal

60
Q

what causes area of contact of placenta with endometrium to shrink?

A

Rapid shrinkage of the uterus after fetal delivery

61
Q

uterine shrinkage causes what two things?

A

folding of fetal membranes

area of contact of placenta with endometrium to shrink

62
Q

clamping of umbilical cord after birth does what?

A

stops fetal blood flow to placenta - villi collapse
Hematoma formation between decidua and placenta
Contractions expel placenta and fetal tissues

63
Q

uterine incolution and cervix repair restore to what?

A

Shielding uterus from commensural bacteria

Restore endometrial cyclicity in response to hormones

64
Q

what facilitates uterine vessel thrombosis

A

uterus remaining contracted

BRS Ageing and Development (3 decks)

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