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brs2 > pregnancy, parturition and late fetal development > Flashcards

pregnancy, parturition and late fetal development Flashcards

1
Q

why is embryo fetal growth during the first trimester relatively limited

A

nutrition is histiotrophic

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2
Q

what is meant by histiotrophic nutrition

A

derivation of nutrients from breakdown of surrounding tissues
reliant on uterine gland secretions and breakdown of endometrial tissues (and maternal capillaries)

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3
Q

what switch in fetal growth takes place from the first to second trimester

A

switch to haemotrophic support at start of 2nd trimester

as foetal growth cannot. be maintained/supported by histiotrophic nutrition

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4
Q

what is haemotrophic support

A

foetus will start to derive its nutrients from maternal blood

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5
Q

what is meant by the haemochorial-type placenta

A

maternal blood is directly in contact with chrorion/one of the foetal membranes
activation is around 12 weeks

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6
Q

what is amniotic sac

A

comes from amnion/amniotic cavity

surrounds and cushions foetus for its development through second and third trimesters

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7
Q

what is the connecting stalk

A

links developing embryo unit to chorion

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8
Q

what is the 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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9
Q

what is the consequence of of breakdown of maternal capillaries and uterine glands

A

creates a continuous space through which maternal blood can flow

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10
Q

what are the fetal membranes

A

extraembryonic tissues that form a tough but flexible sac encapsulates fetus and forms basis of maternal fetal interface
predominantly the amnion fetus

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11
Q

what is the amnion

A

inner fetal membrane-

  • arises from epiblast
  • forms a closed, avascular sac with developing embryo at one end
  • begins to secrete amniotic fluid from 5th week - froms fluid filled sac that encapsulates and protects fetus
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12
Q

what is the chorion

A

outer fetal membrane -

  • formed from yolk sac derivatives and trophoblast
  • highly vascularised
  • gives rise to chorionic villi
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13
Q

what are chorionic villi

A

outgrowths of cytotrophoblast from chorion that forms basis of fetal side of placenta

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14
Q

what happens when accumulation of amniotic fluid causes amnion to be in contact with chorion

A

both form forming amniotic sac which has 2 layers; amnion on inside and chorion on outside

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15
Q

what is the allantois

A

outgrowth of yolk sac
grows along connecting stalk from embryo to chorion
becomes coated in mesoderm and vascularises to form umbilical cord

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16
Q

what are the primary chorionic villi

A

cytotrophoblasts form finger like projections through syncitiotrophoblast layer into maternal endometrium

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17
Q

what are chorionic villi

A

provide substantial surface area for exchange

finger like extensions of chorionic cytotrophoblast which grow into syncitiotrophoblast and undergo branching

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18
Q

what happens in secondary phases of chorionic villi development

A

growth of fetal mesoderm into primary villi

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19
Q

what happens in tertiary phase of chorionic villi development

A

growth of umbilical artery and umbilical vein into villus mesoderm, providing vasculature

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20
Q

describe terminal villus microstructure

A

convoluted knot of vessels and blood vessel dilation-
slows blood flow enabling exchange between maternal and fetal blood
whole structure coated with trophoblasts

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21
Q

what happens to diameter of villi as we move through pregnancy

A

diameter decreases from around 150-200 ym in early pregnancy to 40ym later on
distance from trophoblast to maternal blood also decreases

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22
Q

describe maternal blood supply to endometrium

A

uterine artery branches give rise to network of arcuate arteries
radial arteries branch from arcuate arteries which branch further to form basal arteries
basal arteries form spiral arteries during menstrual cycle endometrial thickening

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23
Q

what is role of spiral arteries

A

provide maternal blood supply to endometrium

24
Q

what are the extra-villus trophoblast(evt) cells

A

coat the villi and invade down into maternal spiral arteries forming endovascular evt
endothelium and smooth muscle is broken down - evt coats inside of vessels

25
Q

what is conversion in spiral artery remodelling

A

turns spiral artery into low pressure high capacity conduit for maternal blood flow

26
Q

what are the nutrients exchanged across placenta

A

oxygen via diffusion gradient
glucose via facilitated diffusion by transporter
water - majority via diffusion
electrolytes - diffusion and active transport
calcium. -active transport
amino acids - active transport

27
Q

what happens to maternal cardiac output during the first trimester

A

increases by 30%
peripheral resistance decreases
maternal blood vol increases to 40% - increase in erythrocyes and plasma
pulmonary ventilation increases 40%

28
Q

describe consumption by fetus/placenta

A

consumes 40-60% glucose and o2 supplied

embryonic and fetal hbs have greater affinity for o2 than maternal hb therefore bind at higher capacity

29
Q

describe circulatory system in late fetal development

A

placenta acts as site of gas exchange
ventricles act in parallel rather than series
vascular shunts bypass pulmonary and hepatic circulation - close at birth

30
Q

describe resp system in late fetal development

A

primitve air sacs form in lungs around 20wks, vascularisation from 28wks
surfactant production begins around 20 wks,
fetal spends 1-4hrs a day making rapid respiratory movements during rem sleep

31
Q

describe gastrointestinal system in late fetal development

A

endocrine pancreas is 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

32
Q

describe nervous system development during late fetal development

A

fetal movements begin in late 1t, detectable by mother from 14 weeks
stress responses from 18wks
does not show conscious wakefulness

33
Q

what is labour

A

safe expulsion of fetus at correct time
expulsion of placenta and fetal membranes
resolution/healing to permit future reproductive events

34
Q

what pre inflammatory reactions do you expect to see in labour

A

immune cell infiltration

inflammatory cytokine and prostaglandin secretion

35
Q

what happens in first stage of labour

A

contractions start, cervix dilation
latent phase - slow dilation of cervix to 2-3cm
active phase - rapid dilation of cervix to 10cm

36
Q

what happens during second stage of labour

A

delivery of foetus
- commences at full dilation of cervix > 10cm
maximal myometrial contractions

37
Q

what happens during third stage of labour

A

delivery of placenta and fetal membranes

post partum repair

38
Q

why does cervix have high connective tissue content

A

provides rigidity

stretch resistant

39
Q

describe other properties of cervix

A

bundles of collagen fibres embedded in proteoglycan matrix

- changes to collagen bundle structure underlie softening, but mechanism unclear

40
Q

when does cervical softening occur

A

first trimester

chnages in compliance but retains cervical competence

41
Q

when does cervical ripening occur

A

weeks and days before birth
- monocyte infiltration and il6,il8 secretion
hylauron depositin

42
Q

what happens during cervical dilation

A

increased elasticity
increased hylauronidase expression - ha breakdown
mmps decrease collagen content

43
Q

what happens to cervix during post partum repair

A

recovery of tissue integrity and competency

44
Q

theories of how labour is initiated

A

fetus determines timing of partruition through chages in fetal hpa axis
cpa levels rise exponentially towards end of pregnancy
- decline in crh binding protein levels so crh bioavailabilty increases

45
Q

what is crh functions in labour

A

promotes fetal acth and cortisol release
increasing cortisol drives placental production of crh
stimulates dheas production by fetal adrenal cortex - substrate for oestrogen production

46
Q

what does estrogen and progesterone levels look like during pregnancy

A

high progesterone maintains uterine relaxation
serum estrogen:progesterone ratio may shift in favour of estrogen
as term approaches switch from PR-A isoforms to PR-B AND PR-C isoforms - functional prog withdrawal
uterus becomes blinded to progesterone action and sensitised to estrogen action
local changes in e:p ratio in uterine tissue

47
Q

what does oxytocin look like in pregancy

A 
uterine production increases sharply
driven by increase in oestrogen
release promoted by stretch receptors - ferguson reflex
signal through otr/oxr g coupled protein
prog inhibits oxtr - uterus is relaxed
48
Q

what is function of oxytocin

A

increases connectivity of myocytes in myometrium
destablises membrane potentials to lower threshold for contraction
enhances liberation of intracellular ca2+ ion stores

49
Q

what is role of prostaglandins in labour

A

key effector of labour
PGE2,PGF2 alpha and PGI2 synthesised during labour
1.rising estrogen activates phospholipase a2 enzymes, generating more arachidonic acid for pg synthesis
2. estrogen stimulation of oxytocin receptor expression promotes pg release

50
Q

what is role of pge2 in cervix remodelling

A

leukocyte infiltration into cervix, il8 release and collagen bundle remodelling

51
Q

what is role of pgf2 alpha

A

myometrial contractions -

destabilises membrane potentials and promotes connectivity of myocytes with oxytocin

52
Q

what is role of pgi2

A

in myometrium

promotes myometrial smooth muscles relaxation and relaxation of lower uterine segment

53
Q

what are some other factors involved in cervix remodelling

A

peptide hormone relaxin and nitric oxide

54
Q

how do myometrial contractions work

A

contractions start from fundus and spread down upper segment
muscle contractions are brachystatic
causes lower segment and cervix to be pulled up forming birth canal

55
Q

what occurs during fetal expulsion

A

head engages with pelvic space within 34-38 wks
pressure on fetus causes chin to press again chest - flexion
fetus rotates
head expelled first

56
Q

what happens during placental expulsion

A

rapid shrinkage of uterus
shrinkage causes folding of foetal membranes
clamping of umbilical cord after birth stops fetal blood flow to placenta
haematoma between decidua and placenta
contractions expel placenta

57
Q

what happens during repair

A

uterus remains contracted to facilitate uterine vessel thrombosis
uterine involution and cervix repair shields uterus from commensal bacteria
endometrial cyclicity is restored in response to hormones

brs2 (65 decks)

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