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When during gestation does the heart begin to beat?
Day 22
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When during gestation does heart looping occur?
Week 4
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What is heart looping?
Folding and ending of a simple heart tube
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The major events resulting in formation of the heart structures are occurring during which period?
Embryonic period
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What is the critical period for heart development?
Mid-week 3 – week 6
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What is the most common type of birth defect?
Congenital heart defects
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From which germ layer does the heart arise from?
Mesoderm, with a bit of ectoderm
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What is dextrocardia?
Heart develops as it’s mirror imaging, with apex pointing to the right
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What causes dextrocardia?
Disruption of the signaling pathway that determines laterality
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How does body folding affect the formation of the heart?
Heart forming region is brought to a ventral position (from a cranial position)
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Where does the heart rank in the order of organs developed in the fetus?
Primitive heart tube is first
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What is the truncus arteriosus?
Outflow region of the primitive heart tube
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What structures will the truncus arteriosus become in the heart?
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What structures will the bulbus cordis become in the heart?
Smooth parts of both ventricles
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What structures will the primitive ventricle become in the heart?
Trabeculated part of both ventricles
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What structures will the primitive atrium become in the heart?
Trabeculated part of both atria
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What structures will the sinus venosus become in the heart?
- Smooth part of right atrium
- Coronary sinus
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What is the order of the embryonic dilations of the primitive heart tube from cranial to caudal?
- Truncus arteriosus
- Bulbus cordis
- Primitive ventricle
- Primitive atrium
- Sinus venosus
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What is heart looping?
The repositioning process happening so that future chambers are placed closer to their final positions
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During heart looping, what are the bending directions of the cranial portion of the heart tube?
Bends ventrally, caudally, and to the right
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During heart looping, what are the bending directions of the caudal portion of the heart tube?
Bends dorsally, cranially, and to the left
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What is partitioning of the heart?
Building internal anatomy to separate the chambers
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What are the key events in partitioning of the heart?
- Endocardial cushions divide AV canal
- Atrial septation
- Ventricular septation
- Remodeling of the outflow tracts
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When in development does endocardial cushions divide the AV canal?
Weeks 4-5
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When in development does atrial septation occur?
Weeks 4-5
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When in development does ventricular septation occur?
Weeks 4-5
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What is the atrioventricular canal?
Junction between the future atria and future ventricles
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Describe the process of endocardial cushions dividing the AV canal
Superior endocardial cushion and inferior endocardial cushion grow towards each other and divide the AV canal into a left and right AV canal
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What is an endocardial cushion defect?
Atria and ventricles connected centrally
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What is the first wall built in the heart?
Septum primum
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What is the ostium primum?
Gap between septum primum and endocardial cushions
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What is the septum secundum?
Second wall that forms and overlaps the septum primum
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The opening left by the septum secundum is called the ___________________
Foramen ovale
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What happens to the septum primum and septum secundum?
- Upper part of septum primum disappears and remaining part becomes valve for foramen ovale
- Septum secundum becomes foramen ovale
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Describe the process of ventricular septation
- Interventricular septum grows toward endocardial cushions
- Interventricular foramen closed by membranous IV septum
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What is an atrial septal defect?
Hole between atria does not close (heart murmur heard)
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In an atrial septal defect, does blood flow right to left or left to right? Why?
- Left to right
- Higher pressure on left side
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What is a ventricular septal defect? In which direction does blood usually flow?
- Hole between atria and ventricles
- Left to right
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Why is it common for people with congenital facial deformities to also have congenital heart defects?
Neural crest cells involved in both facial development and heart development
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Describe remodeling of the outflow tracts
Neural crest cells grow into ridges that twist and fuse to form aorticopulmonary septum (divides truncus arteriosus into aorta and pulmonary trunk)
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What is transposition of the great arteries (TGA)?
Pulmonary aorta and aorta are switched so oxygenated blood goes to lungs and deoxygenated blood goes to body
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What is the treatment for TGA?
Hole made in atrial septum to let blood mix, then surgery to switch the arteries
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What is tetralogy of Fallot?
- Ventricular septal defect: hole between ventricles
- Pulmonary stenosis: narrowing of pulmonary artery and valve
- Overriding aorta: aorta enlarged and open to both ventricles
- Ventricular hypertrophy: right ventricle muscular wall bigger
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What causes tetralogy of Fallot?
Unequal growth of the aorticopulmonary septum
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In, tetralogy of Fallot, in which direction does the blood usually flow in the ventricles? Why?
- Right to left
- Increased resistance of blood flowing into pulmonary artery because of stenosis
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What kind of heart defects can cause cyanosis?
Those that cause blood shunt from right to left side
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What are tet spells?
Hypercontractile episodes leading to cyanosis in tetralogy of Fallot
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List and describe the three fetal shunts?
- Ductus venosus: from umbilical vein to IVC
- Foramen ovale: from right to left atrium
- Ductus arteriosus: from pulmonary trunk to aorta
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What are the embryonic remnants of fetal circulation?
- Ligamentum venosum: remnant of ductus venosus
- Fossa ovalis: remnant of foramen ovale
- Ligamentum arteriosum: remnant of ductus arteriosus
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What is a patent ductus arteriosus? How is it treated?
- Ductus arteriosus does not close
- Treated with NSAIDs to the neonate
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