Repro 9 Flashcards
How is blood mixing between deoxygenated blood from the SVC and oxygenated from the IVC in the fetal heart prevented as it enters the right atrium?
by the crista dividens= directs oxygenated blood towards foramen ovale to pass in to LA, then LV, and out through aorta to supply head structures e.g. brain
why is there little blood flow from the lungs into the left atrium in the fetal heart?
very high resistance pulmonary circulation so moost blood entering pulmonary artery from RV travels through the ductus arteriosus into the aorta, bypassing the lungs
what 2 things is the pattern of fetal circulation dependent on?
pressure in RA being greater than LA so oxygenated blood can pass all way across foramen ovale into LA
pressure in PA being greater than that in aorta so that blood from the RV can bypass the lungs to flow into the aorta to supply the rest of the fetal body, and be returned to the placenta for oxygenation
how are the necessary pressures for the pattern of fetal circulation met?
by the high flow resistance of the lungs
via what blood vessels is deoxygenated blood from the fetus returned to the placenta?
umbilical artery
how does blood travelling from the placenta to the fetus bypass the liver?
via the ductus venosus
oxygenated blood entering IVC from placenta, via umbilical vein, mixes with what blood before entry into RA, and why is this not a problem?
venous blood from lower body of fetus but lower body relatively small and not that active metabolically, so there isn’t much loss of oxygenation
how does oxygenated blood from maternal circulation provide oxygen to fetal blood in the fetal circulation to supply the fetal brain?
maternal blood passes through the remodelled spiral arteries of the endometrium of the uterus, to enter the intervillous spaces of the placenta where O2 diffuses across the syncytium of the villus, into the fetal capillaries located in the core of the villus, to then travel via the umbilical vein into the fetal circulation, as the umbilical vein passes through the umbilical cord. This venous blood enters the IVC, bypassing the liver via the ductus venosus and enters the RA, where it can then pass across the foramen ovale, into the LA, LV then out through the aorta to supply the brain.
how is the fetus adapted to a degree of hypoxia?
different Hb- fetal has higher O2 affinity and carries more O2 at lower pO2
higher Hb
how is fetal blood oxygenated at the placenta?
returned to placenta via umbilical arteries, which then allow the deoxygenated blood to pass into the fetal capillaries at the core of the villus, where blood is then oxygenated by O2 diffusion across the syncytium from the maternal blood bathing the villus that has entered the intervillous spaces from branches of maternal spiral arteries
how does maternal changes allow fetus to have relatively normal pCO2?
progesterone stimulated hyperventilation to remove metabolic CO2 produced by fetus
how might a baby with respiratory distress syndrome appear and why?
bluish discolouration of tongue and lips- central cyanosis:
- Lack of surfactant means increased surface tension, so the lungs are harder to inflate and fill with air as reduced lung compliance.
- There will be many collapsed alveoli as smaller alveoli collapse into larger ones due to lack of surfactant meaning increased surface tension and hence pressure, especially in the smaller alveoli as they have a smaller radius so increased pressure, so many alveoli can’t take part in GE, there is ventilation/perfusion mismatch, resulting in arterial hypoxia.
when does fetal insulin secretion commence?
wk 10
why does fetal bilirubin pass across the mum?
as unconjugated as cannot be excreted by fetal gut
cause of polyhydramnios?
oesophageal atresia- so amniotic fluid unable to be swallowed by fetus
antenatal bartter syndrome- problem with ATL of loop of Henle so excess urine production
duodenal atresia
CNS abnormalities
tracheooesophageal fistula
why might amniocentesis be used to assess amniotic fluid?
to assess presence of neural tube defects or Down’s syndrome
how are amniotic fluid volumes assessed?
ultrasound
what may cause oligohydramnios?
poor/absent fetal renal function
pre-eclampsia- example of reduced placental function
based on NS development, why are low thyroid hormone levels at birth dangerous?
cretinism- poor neurological development of neonate as hormones requried for completion of myelination which does not occur until into post-natal period
T3 and T4 necessary also for hyperplasia of cortical neurones and development of processes of neurones in NS development
what do thyroid hormones mediate in fetus from wk 12?
bone, hair growth, and NS development
what promotes fetal corticosteroid prod?
placental progesterone
how does dramatic decrease in pulmonary vascular resistance occur at birth?
baby takes its 1st breath due to combination of physical trauma and cold temps, opening the alveoli
how does taking 1st breath close ductus arteriosus?
smooth muscles in wall of DA sensitive to high pO2 contracts
what regulates closing of DV after birth via sphincter in vessel?
pO2 levels
what is the fetal period?
stage of intra-uterine life from end of 8th week till term
how is intrauterine growth restriction suggested in height measurement?
lag of 4cm or more of the fundal height
characterisitcs of lungs that fetal survival depends on?
thin walled air sacs for GE
surfactant to lower surface tension and allow air sacs to expand
4 stages histologically of lung maturation influencing viability of premature infants?
pseudoglandular- not viable
canalicular- may be viable at end
terminal sac
alveolar period
how is fetal urinary function assessed clinically?
use ultrasound to look at bladder emptying in fetus, with urine emptying into amniotic fluid
sources of variability in measurement of symphysis-fundal height?
lie of fetus
number of fetus
volume of amniotic fluid
extent of engagement of head
factors impacting on fetal growth?
Maternal nutrition and health
Efficiency of placenta
Adequate utero-placental blood flow
Genetic factors
Maternal parity (primaparous mothers have smaller babies than multiparous)
Maternal habits (smoking, drug abuse etc)
Also, race, maternal height, weight,
how can uteroplacental circulation be assessed?
doppler ultrasound scan
why is an US scan at 20 wks in pregnant mothers a good time?
At this stage of pregnancy the organ systems are developed and can be visualised and anomalies can be identified.
ii. If anomalies are seen, the pregnancy is still early enough for possible intervention or
termination if appropriate.
iii. The inherent error in these measurements increases with gestational age such that
as a dating tool ultrasound becomes less accurate as the pregnancy proceeds.
uses of US in obstetrics, other than 20 wk scan?
Determine presence or absence of intrauterine pregnancy (or ectopic pregnancy)
Determine gestational age and measure fetal growth (when compared against standard
tables)
e.g., abdominal circumference (AC)
Identify multiple pregnancies
Detect fetal anomalies (e.g., neural tube defects), placental anomalies (e.g., placenta praevia)
Measurement of amniotic fluid
(Identify maternal pelvic anomalies)
(Guide for needle in amniocentesis)
why use a transvaginal US in early pregnancy if expectant mother has had severeal pregancy losses before?
see fetal cardiac activity in uterus which is very reassuring
rules out ectopic pregnancy
what can raised alpha fetoprotein levels be indicative of in pregnancy?
multiple pregnancy
open neural tube defect
why is folic acid used in pregnancy?
reduce risk of neural tube defects
what can be given to mums antenatally to reduce risk of RDS if at risk of pre-term delivery?
steroid therapy to promote surfactant production, with production starting at around 20 wks
why is the symphysis-fundal height used in pregnancy assessment?
The uterus becomes an abdominal organ at about 12 weeks so the fundus is now palpable.
The height from top of symphysis pubis to top of fundus (in cm) correlates with the number
of weeks of gestation
use of fetal abdominal circumference measurement?
Measurement of fetal waist (at level of the umbilical vein) provides assessment of growth of
fetal liver and amount of sub-cutaneous fat etc. Glycogen laid down in the fetal liver
accounts for much of this growth.
what is meconium and how is it formed?
Typically, meconium are the first stools of a newborn baby – green, dark and sticky and
composed of cellular debris, mucous and bile pigments. It is formed from the digestion
products of amniotic fluid (cells and protein) the fetus has swallowed. The presence of
meconium in the amniotic fluid is an indicator that the fetus has had an episode of distress