Repro 8 Flashcards
importance of anti-insulin hormones during pregnancy e.g. oestrogens, progesterone, placental lactogen?
Make muscles resistant to insulin as muscle would use glucose straight away for ATP production which would reduce the concentration gradient of glucose, and we want glucose to go to AT wheres stored as fat
how are nutrients transferred across placenta to foetus?
by diffusion- so rate of transfer dependent on nutrient conc in maternal circulation
Metabolic and hormonal response in 1st half of pregnancy?
anabolic state: preparatory increase in maternal nutrient stores ready for rapid growth of foetus, birth and subsequent lactation. Increase insulin:anti-insulin, so increased nutrient storage
Metabolic and hormonal response in 2nd half of pregnancy?
marked increase in growth of placenta and foetus. Demands of foetal-placental unit met by reducing maternal utilisation of glucose by switching tissues to FA, delaying maternal disposal of nutrients after meals and releasing FA from built stores after 1st half of pregnancy.
Maternal insulin continues to rise but anti-insulin also increases at an even faster rate, so ratio falls to produce required met. changes
Result of reduction in insulin:anti-insulin coupled with increased availability of FA from maternal AT?
KB production by maternal liver, which can be used as fuel by developing foetal brain.
*KB able to cross BB barrier
how does gestational diabetes result?
beta cells of endocrine pancreas unable to meet increased demand for insulin via hyperplasia and hypertrophy and increased rate if insulin synthesis, so lose control of met., with increase in blood glucose and subsequent diabetes.
possible consequence of gestational diabetes on baby?
macrosomia- fat baby with lots of liver and muscle glycogen, can make delivery difficult
what are the functional units of the placenta?
chorionic villi= point of exchange between maternal and foetal circulations
hCG is only released from the syncytiotrophoblast around 14 days after ovulation, what occurs with the corpus luteum before this time?
The corpus luteus is formed under LH stimulation and has a lifespan of 14 days until it spontaneously regresses unless hCG is produced by the placenta. Therefore, oestrogen and progesterone are secreted from the corpus luteum before hCG signals the necessity for the corpus luteum to remain to continue producing these hormones
aims of implantation?
establish basic unit of exchange= chorionic villi
anchor placenta via outermost trophoblast shell
establish maternal bflow within the placenta
function of decidual reaction?
provide balancing force for invasive force of trophoblast
why can continuous invasion occur in an ectopic preganancy?
implantation outside of endometrium, so no decidual reaction to provide balancing force for invasive force of trophoblast
2 components of placenta?
chorion frondosum
decidua basalis
importance of decidual cells?
manage depth of invasion, and facilitate spiral artery remodelling
2 mechanisms for efficient exchange across term placenta?
large SA provided by continued branching of villi
cytotrophoblast layer lost beneath syncytiotrophoblast
4 components of 1st trimester placental membrane?
endothelium of fetal blood vessels
CT core of villus
cytotrophoblast layer
syncytiotrophoblast
why is hCG used as the basis of pregnancy testing?
pregnancy specific as secreted by syncytiotrophoblast during 1st 2mnths of pregnancy
and excreted in maternal urine so can be measured from 2 wks following fertilisation (in serum from 7 days)
what factors influence the passive diffusion of substances across the placenta?
- Concentration Gradient-The steeper the gradient, the more diffusion, and this is maintained by constancy of flow
- Barrier/resistance to diffusion-placental membrane gradually thins throughout pregnancy as the demand of the fetus increases, so cytotrophoblast diasappears beneath syncytium, reducing diffusion distance- haemomonochorial
- SA available- markedly increased by branching of villi, and microvilli on maternal surface of syncytiotrophoblast
function of placenta in metabolism?
synthesises glycogen- for itself and use before utero-placental circulation established
cholesterol- for steroid hormone synthesis- oestrogen and progesterone
FA
endocrine function of placenta?
proteins: hCG, hCsomatomammotrophin, human chorionic thyrotrophin, human chorionic corticotrophin
steroid: progesterone and oestrogen
when does placenta take over from corpus luteum to maintain pregnant state by steroid hormone prod.?
by the 11th wk (end of 1st trimester)
how does progesterone influence maternal met.?
increases appetitie
how do hCS and human placental lactogen influence maternal met.?
increase glucose availability to fetus
which molecules move by simple diffusion across the placenta?
water
electrolytes
urea and uric acid
gases
which molecule moves by facilitated diffusion across placenta?
glucose
adequate conc gradient must be maintained
what is actively transported across the placenta?
iron
aa
vitamins, via specific transporters expressed by syncytiotrophoblast
what substances are transported across the placenta via receptor-mediated endocytosis?-clathrin coated pits, endosome, lysosome etc.
IgG
Ig found in breast milk?
IgA
what limits the diffusion of gases across the placenta?
FLOW not diffusion
fetal O2 stores small so must maintain adequate flow- low resistance, high flow utero-placental circulation via modification of spiral arteries
circulation can be compromised with large uterine contractions in labour
drugs capable of crossing the placenta?
thalidomide alcohol therapeutic drugs- warfarin, anti-convulsants, all teratogenic drugs of abuse maternal smoking- lowers birth weights
infectious agents able to cross placenta?
varicella-zoster cytomegalovirus tremponema pallidum-syphilis toxoplasma gondii rubella- maternal rubella syndrome- RNA enveloped virus, most common cause of PDA if mother infectied during 1st trimester, DA closed with NSAIDs- inhibt PG prod and PG cause vasodilation that would keep DA patent
why does haemolytic disease of the newborn occur?
rhesus incompatibility of mother and fetus, if rhesus -ve mother and rhesus +ve fetus. If mother has been sensitised to rhesus antigen e.g. in previous pregnancy, her body’s immune system can mount a response to the antigen by producing antibodies, which can cross the placenta to bind to rhesus antigen on surface of rbc, mediating their destruction, producing a haemolytic anaemia.
However, rare now as prophylactic tment given e.g. Rhesus –‘ve mothers pregnant with Rhesus +’ve fetus given Rhesus specific IgG throughout pregnancy, to prevent sensitisation in the event of exposure to the antigen (The given IgG will bind to antigen before the mother’s immune system can mount a response), can also be given anti-D therapy after birth of baby to mother to prevent rhesus disease in further children*
how does the syncytiotrophoblast invade the endometrium to allow implantation to have begun by day 6?
it secretes enzymes similar to those secreted by metastatic tumours to allow the interstitial process of implantation
In pregnancy, the conceptus has embedded within the endometrium before the date of the next expected menses, true or false?
True
by day 9, the conceptus has implanted and so this is less than 2 wks following fertilisation, and hence before the next expected menses which occurs 2 wks after ovulation due to the lifespan of the corpus luteum
which membrane ruptures at the onset of labour?
composite amniochorion membrane, causing amniotic fluid leakage, as amniotic sac enlarges with growth and development of fetus, coming to lie in close contact with the chorionic sac
how does the placenta provide passive maternal immunity to the neonate in pregnancy?
allows transport of IgG by receptor-mediated endocytosis from the maternal circulation to the fetal circulation. This begins at approximately 14 weeks and eventually the concentration of IgG in fetal plasma exceeds that of maternal plasma.
In this manner the fetus gains passive immunity against various infectious diseases. Newborns produce their own IgG, but adult levels are not attained until the age of 3- from 3, susceptibility to meningitis caused by N.meningitidis.
negatives on mother of hCG reducing maternal IgG, IgA and IgM?
more susceptible to infection
why might action of hCG to reduce maternal Igs in pregnancy be beneficial to fetal-placental unit?
stop rejection of placenta by mother and vice-versa
components of antenatal screening?
history and exam: RFs e.g. for gestational diabetes- age, weight, high BP, FH
blood test- blood group, Hb- already anaemic?, infection e.g. HIV, syphillis, chlamydia- can be transmitted to fetus at delivery
urinalysis- proteinuria- indicative of renal failure, may be result of pre-eclampsia as vasoconstricition cause poor perfusion to kidneys
why does blood volume increase in pregnancy?
coping with a new circulation- utero-placental circulation must be supplied in order to supply blood, and hence nutrients and O2 to the fetus
must increase b.flow to kidneys
anticipatory increase for blood lost during fetal delivery
normal auscultatory changes noted in pregnancy?
mild tricuspid regurgitation- systolic murmur- S1
shifted apex beat due to shifted diaphragm
effects of increased blood volume on HR, SV and CO in pregnancy?
ALL INCREASE
increased blood volume- most blood in veins, so increased venous return to heart, so increased CVP hence SV under Starling’s Law as myocardial fibres stretched more, increasing force of contraction, which increases SV and CO, and HR must increase to prevent volume overload on heart?
hypotension due to progesterone effects, SNS activation to increase HR?*
why does reduced cardiac output occur in pregnancy if mother supine?
uterus compresses IVC, reducing venous return to heart, so less blood pumped out, reducing CO
why is the syncytiotrophoblast good at transport?
it is a huge multi-nucleated sheet, which minimises the total number of intracellular barriers.
the cells are directly bathed in maternal blood in the mature placenta when the underlying cytotrophoblast disappears
increased Hb needed in vol expansion, how does this occur?
increased Fe absorption
what mediates blood vol. increase in pregnancy?
RAAS
placental oestrogen increases angiotensinogen prod by liver, and renin prod increased by oestrogen and progesterone. Aldosterone stim release from zona glomerulosa, causing Na+ and H20 retention
thirst also increased
why is hypotension seen in 1st 2 trimesters of pregnancy?
progesterone effect on smooth muscle, causing relaxation hence vasodilation, decreasing TPR and hence BP
also loss of peripheral responsiveness to AngII accompanying increase in blood vol
substance responsible for decrease sytemic vascular resistance in pregnancy?
progesterone- high levels from early on in pregnancy