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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
what is conversion in spiral artery remodelling
turns spiral artery into low pressure high capacity conduit for maternal blood flow
26
what are the nutrients exchanged across placenta
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
what happens to maternal cardiac output during the first trimester
increases by 30% peripheral resistance decreases maternal blood vol increases to 40% - increase in erythrocyes and plasma pulmonary ventilation increases 40%
28
describe consumption by fetus/placenta
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
describe circulatory system in late fetal development
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
describe resp system in late fetal development
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
describe gastrointestinal system in late fetal development
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
describe nervous system development during late fetal development
fetal movements begin in late 1t, detectable by mother from 14 weeks stress responses from 18wks does not show conscious wakefulness
33
what is labour
safe expulsion of fetus at correct time expulsion of placenta and fetal membranes resolution/healing to permit future reproductive events
34
what pre inflammatory reactions do you expect to see in labour
immune cell infiltration | inflammatory cytokine and prostaglandin secretion
35
what happens in first stage of labour
contractions start, cervix dilation latent phase - slow dilation of cervix to 2-3cm active phase - rapid dilation of cervix to 10cm
36
what happens during second stage of labour
delivery of foetus - commences at full dilation of cervix > 10cm maximal myometrial contractions
37
what happens during third stage of labour
delivery of placenta and fetal membranes | post partum repair
38
why does cervix have high connective tissue content
provides rigidity | stretch resistant
39
describe other properties of cervix
bundles of collagen fibres embedded in proteoglycan matrix | - changes to collagen bundle structure underlie softening, but mechanism unclear
40
when does cervical softening occur
first trimester | chnages in compliance but retains cervical competence
41
when does cervical ripening occur
weeks and days before birth - monocyte infiltration and il6,il8 secretion hylauron depositin
42
what happens during cervical dilation
increased elasticity increased hylauronidase expression - ha breakdown mmps decrease collagen content
43
what happens to cervix during post partum repair
recovery of tissue integrity and competency
44
theories of how labour is initiated
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
what is crh functions in labour
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
what does estrogen and progesterone levels look like during pregnancy
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
what does oxytocin look like in pregancy
``` 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
what is function of oxytocin
increases connectivity of myocytes in myometrium destablises membrane potentials to lower threshold for contraction enhances liberation of intracellular ca2+ ion stores
49
what is role of prostaglandins in labour
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
what is role of pge2 in cervix remodelling
leukocyte infiltration into cervix, il8 release and collagen bundle remodelling
51
what is role of pgf2 alpha
myometrial contractions - | destabilises membrane potentials and promotes connectivity of myocytes with oxytocin
52
what is role of pgi2
in myometrium | promotes myometrial smooth muscles relaxation and relaxation of lower uterine segment
53
what are some other factors involved in cervix remodelling
peptide hormone relaxin and nitric oxide
54
how do myometrial contractions work
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
what occurs during fetal expulsion
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
what happens during placental expulsion
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
what happens during repair
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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