Development of The Heart

*Development of heart tube

-Heart tube develops from lateral mesoderm

-Endoderm releases growth factor (vascular endothelial growth factor) which stimulates lateral plate mesoderm to start differentiating and specializing

-From lateral plate mesoderm, there are some chunks grow off it

+The chunks from the back will fuse with each other to form pericardial cavity

+The chunks from the front will fuse with each other to form heart tube 

-Pericardial cavity connects to heart tube through dorsal mesocardium 

*Structure of heart tube

-In the order from the top to the bottom

+Aortic sac develops into dorsal aortae

+Truncus arteriosus develops into pulmonary trunk and aortic arch

+Bulbus cordis develops into right ventricle 

+Primitive ventricle develops into left ventricle

+Primitive atria develops into left and right atrium

+Sinus venosus develops into common cardinal veins, umbilical veins, and vitelline veins

*Cardiac looping process

-Truncus arteriosus moves down and to the right

-Primitive ventricle moves towards the left of the midline while primitive atria moves backwards

-Sinus venosus allows some of the cells in nearby areas moving into the pericardial cavity and form visceral pericardium

-Some of these cells also infiltrates into the heart and form small primitive conduction system which allows heart to beat

*Separation of primitive atria and ventricle

-Neural crest cells start migrating and forming endocardial cushions. Later on, they will fuse together to form a canal (septum intermedium) 

-Coming off of the septum intermedium, some of the endocardial cells start forming little valves. Valvular apparatus connected septum with valves. Chordae tendanea comes off of those valve flaps

-The left one is mitral valve and the right one is tricuspid valve

-There is tissue that tries to grow downwards from the top of primitive atria down towards the septum (septum primum). However, there is still a hole called ostium secundum, so one more tissue will grow near the septum primum to block the hole——> forming right and left atrium

-At the apex of the heart, some tissue moves upwards and develops into a structure called the muscular portion of the interventricular septum. From the septum, there is also some tissue moving downwards and fuse with the muscular portion of interventricular septum——->Forming right and left ventricles

-After that, inferior and superior vena cava will develop while aorta and pulmonary trunk will separate from each other