Embryonic heart development Flashcards
How does the heart develop
Develops from cardiogenic plate of mesodermal tissue at cranial end of embryonic disc
Tube grows quicker than rest of embryo
Normally folds to the right (D-looping)
Falling to left (L-looping) is abnormal
Label the cardiac tube
What is the role of endocardial cushions
Endocardial cushions in AV canal form chordae tendinae & AV valves
Mitral/tricuspid dysplasia causes a murmur
What does the bulbous cordis form
Bulbar cushions in bulbous cordis & truncal cushions in truncus arteriosus fuse to form aorticopulmonary septum
Also contributes to interventricular septum
Persistent truncus arteriosus = PA & aorta don’t divide
Explain processes by which partitioning of AV canal, atrium & ventricle occur
- Formation of atrioventricular canal
Connects primitive atria & ventricles - Septation of atria & ventricles
Endocardial cushions in AV canal fuse & separate AV canal into 2 openings
Future mitral & tricuspid valves - Formation of atrial septum
Grows downwards & divides common atrium into left & right atria
Fuses with endocardial cushions - Formation of ventricular septum
Interventricular septum grows upwards & fuses with endocardial cushions to form right & left chambers of ventricle - Valve formation
How many chambers do fish, amphibians & birds have
Fish – 2 chambers
Amphibian heart – 3 chambers (2 atria, 1 ventricle)
Birds – 4 chambers
What are the 3 main shunts in fetal circulation called
Ductus venosus
Foramen ovale
Ductus arteriosus
What is the role of the foramen ovale
Shunts oxygenated blood through RA to LA
Pressure difference across FO keeps it open in fetus
Receives blood directly from umbilical vein
Blood goes straight up to brain & then back to heart
What is the role of the ductus arteriosus
Shunts blood in pulmonary artery straight to descending aorta
Pressure difference between lungs & lower body streams flow back to placenta
Allows right ventricle to work at full capacity to aid muscle development
What is the role of the ductus venosus
Creates low resistance pathway through liver from umbilical vein to caudal vena cava
Not present in fetal horses
How does fetal circulation differ to adults
Fetus breathes amniotic fluid – pulmonary artery doesn’t carry oxygen
Fetal blood is oxygen poor
Fetus swims in amniotic fluid – stable temperature
Fetus is fed parentally – hepatic portal vein not needed
What changes occur upon parturition
Respiration starts
Fetal circulation now closed system
Digestion begins
Thermoregulation
Kidneys need to rid waste
Describe the fate of the ductus venosus
No blood in umbilical vein so DV constricts
Blood diverted through hepatic portal vein (liver)
Happens due to reduction in PGE2 (vasodilator)
Functional closure in minutes
Anatomical closure within days
Describe the fate of the foramen ovale
Closes & fuses as blood is diverted to lungs via right ventricle
Remnant called fossa ovalis
Functional closure within hours
Anatomical closure within weeks-years (small opening persists in 25% of mammals)
Failure to close results in atrial-sepral defect
Describe the fate of the ductus arteriosus
Shuts due to PGE2 removal & promotion of contractile influences
Takes 1-3 days
Failure to close results in ventricular septal defect (not life threatening)
