Maternal-Foetal and Placental Physiology Flashcards Preview

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Flashcards in Maternal-Foetal and Placental Physiology Deck (40)
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What is the primary metabolic substrate for placental metabolism?

Glucose is the single primary metabolic substrate for placental metabolism


How is glucose transferred across the placenta?

Facilitated diffusion


How are amino acids transferred across the placenta?

Active transport: higher concentration in foetus than in the mother


What does the placenta produce?

Oestrogen, progesterone, hCG and hPL


Where does oxygenation of foetal blood occur?

Placenta, NOT lungs


What is the pathway of oxygen blood to the foetus?

Oxygenated blood carried from placenta to the foetus through the umbilical vein, which enters the portal system of the foetus and branches to left lobe of liver. another branch joins blood flow from portal vein to R lobe of liver.


What does the umbilical vein become?

Origin of the ductus venosus


What happens to blood passing through the foetal right ventricle?

-Less than 10% to pulmonary vasculature
-Majority shunted through ductus arteriosus and descending aorta


How does umbilical blood flow relate to foetal size?

Umbilical blood flow represents 40% of combined output of both foetal ventricles. Proportional to foetal growth in last half of pregnancy (~300mL/mg per minute).
i.e. relatively constant, normalised to foetal weight.


What is foetal Hb comprised of?

HbF = a2, y2


What is the key physiologic difference between HbA and HbF?

At any given oxygen tension, HbF has higher oxygen affinity and oxygen saturation than HbA.


Describe O2 / CO2 exchange between mother and foetus?

-Maternal respiratory alkalosis facilitates transfer of CO2 from foetus
-Loss of CO2 from foetus causes rise in foetal blood pH, shifting foetal oxygen dissociation curve to left and increasing O2 binding affinity.


Describe the foetal renal system

-Functional in 2nd T
-Produces dilute, hypotonic urine
-Urine production varies with size (400 - 1200mL / day)
-Primary source of amniotic fluid by middle of 2nd T


Describe the foetal liver

-Slow to mature
-Capacity for glycogen synthesis and bilirubin conjugation increases with gestational age (so bilirubin primarily eliminated through placenta)
-Coag factor synthesis deficient, may be attenuated in newborn due to VitK deficiency


How does the foetal thryoid rely on the mother?

-Mother only primary source of T3/T4 prior to 24 - 28 weeks
-Placenta does not transport TSH
-Gland develops without direct influence from mother, functional by end of first trimester


What does testicular differentiation rely on?

Presence of H-Y antigen and Y chromosome


Why does the mother not reject the antigenically dissimilar foetus?

Appears to be due to placenta
-maintaining separation of foetal and maternal compartments, keeping foetus from contact with maternal immune system
-production of oestrogen, progesterone, hCG, hPL locally decreasing immunity
-producing blocking and masking Abs


What is the major foetal immunoglobulin?

Only maternal IgG can cross the placenta hence maternal IgG major proportion of foetal immunoglobulin


What is the incidence of monozygotic twinning?

One in 250


What are the different influences on monozygotic v dyzygotic twinning?

-Mono: not affected by race, heredity, age, parity or infertility agents.
-Dizygotic: affected by all agents


When will MZ twins be dichorionic and diamniotic?

if there is separation of the blastocyst within the first 72h


What will result if division of the embryo occurs between days 4 - 8?

Monochorionic, diamniotic


When do conjoined twins occur?

MZ twins with late division after formation of the embryonic disk


What happens to deoxygenated foetal blood?

Returned to placenta through the umbilical branches of the two hypogastric arteries. Umbilical arteries exit ado wall at umbilicus and continue through cord to placenta.


Which condition increases incidence of SUA?

SUA increased in diabetic mothers


What does SUA increase?

Risk of foetal malformations (up to 18%) usually involving cardiac and renal systems.


Woman with appearance of spidery veins on face, arms, chest during later pregnancy. Mx?

-vascular spiders / angiomas common findings during pregnancy
- due to hyper oestrogenism
-no further workup / Rx; will resolve after delivery


Why should pregnant women take iron in a multivitamin?

Even if not currently anaemic, amount of iron in diet and that can be mobilised insufficient to meet demands of pregnancy.
-pregnant woman with normal haematocrit at start of pregnancy will develop iron deficiency in latter part of gestation


When do iron requirements increase significantly during pregnancy?

Second half of pregnancy


Will the foetus suffer if maternal iron supplementation does not occur during pregnancy?

No. Placenta will transport required iron at expense of mother.