Prework 3: Fetal Circulation and Congenital Heart Defects

Question 1

describe the general fetal circulation

Answer 1

blood is oxygenated in the placenta and delivered to the embryo via the umbilical vein
most blood passes through the ductus venosus within the liver and returns to the RA via the IVC
blood returns to the placenta via 2 umbilical arteries

Question 2

what is the right to left fetal shunt?

Answer 2

blood shunted from RA to LA via foramen ovale
shunted from pulm outflow to aortic arch via ductus arteriosus
lung bypasses

Question 3

what happens with the first breaths at birth

Answer 3

bradykinin is released from lungs
vascular resistance is decreased in lungs
increased O2 levels cause smooth muscle to contract, increasing blood flow to lungs

Question 4

what is the result of increasing blood flow to the lungs?

Answer 4

increased blood returning from lungs into the LA

significant increase in LA pressure

Question 5

why does the pressure in the RA decrease after birth?

Answer 5

blood flow to the RA decreased because blood flow from placenta is lost when cord is cut

Question 6

result of LA pressure > RA pressure

Answer 6

septum primum is pushed against septum secundum closing the foramen ovale
anatomically closes within 1 year

Question 7

normal closure of ductus arteriosus

Answer 7

functionally closes within 36 h of birth due to loss of prostaglandin E
anatomically closes within 3 months forming ligamentum arteriosum

Question 8

symptoms of patent DA

Answer 8

rapid breathing
increase in the work of breathing
rapid HR
more frequent respiratory infections
tiring more easily
poor eating/growth

Question 9

what population is prone to PDA and what is a treatment?

Answer 9

premature infants are slower in closing the DA

indomethican, a prostaglandin inhibitor can be given to speed closure

Question 10

epidemiology of congenital heart defects

Answer 10

heart and vascular abnormalities make up largest category of birth defects
1% of liveborn infants
incidence 10x higher in stillborns

Question 11

inherited defects that affect heart development

Answer 11

genes that encode transcription factors
cause partial loss of function
autosomal dominant
6-10% of babies with CHDs have chromosomal abnormalities (associated with genetic syndromes)

Question 12

environmental stresses and CHDs

Answer 12

during 1st trimester, these stresses can alter the same genes and conceivably lead to acquired defects that mimic those produced by heritable mutations

Question 13

maternal diseases linked to heart defects

Answer 13

insulin dependent diabetes

hypertension

Question 14

shunt

Answer 14

abnormal communication between chambers or blood vessels

allows blood to flow down pressure gradients

Question 15

obstruction

Answer 15

abnormal narrowing of chambers, valves, or blood vessels

Question 16

atresia

Answer 16

complete obstruction of chambers, valves blood vessels

Question 17

hypertrophy

Answer 17

increase in muscle mass of cardiac chamber (increased size of cells)

Question 18

hypoplasia

Answer 18

decrease in muscle mass of cardiac chamber (fewer cells) BEFORE birth

Question 19

atrophy

Answer 19

decrease in volume and muscle mass of cardiac chamber (degeneration of cells) AFTER birth

Question 20

left to right shunt examples

Answer 20

systemic to pulmonary
ASD
VSD
PDA

Question 21

right to left shunt examples

Answer 21

TOF
transposition of great arteries
persistent truncus arteriosus (common arterial trunk)

Question 22

obstruction examples

Answer 22

coarctation of the aorta

valvular stenosis or atresia

Question 23

effects of left to right shunt

Answer 23

increased pulm blood flow
not initially associated with cyanosis
chronically elevates both V and P in pulm circulation, leading to medial hypertrophy of pulmonary arteries and vasoconstriction
RVH results

Question 24

end stage of left to right shunt

Answer 24

Eisenmenger syndrome
pulmonary resistance approaches systemic levels
left to right shunt becomes a right to left shunt

Question 25

effects of right to left shunt

Answer 25

pulmonary circulation is bypassed, thus decreasing pulmonary blood flow
poorly oxygenated venous blood enters the systemic arterial system
hypoxia and cyanosis results

Question 26

paradoxical embolism

Answer 26

emboli from venous circulation bypass the lungs and enter the systemic circulation
happen in right to left shunts