Development of the Heart and Great Vessels Flashcards
Explain what happens after the lateral plate mesoderm divides into visceral and somatic layers
- in visceral layer angiogenic cell clusters called blood islands appear
- these cells will differentiate into primordial vascular system, heart tube, vessels and primordial erythrocytes
Explain how the right and left heart tubes form from blood islands
- blood islands coalesce and give rise to right and left endocardial tubes and dorsal aorta
- meanwhile part of mesoderm differentiates into cardiomyocytes
Explain folding of the embryo
- day 20, visceral layers of lateral plate mesoderm approach each other
- folds fuse along ventral midline
- space between visceral and somatic mesoderm becomes intraembryonic coelom which later becomes the pericardial cavity
Explain how the right and left endocardial tubes fuse together after folding of the embryo
- endocardial tubes and surrounding cardiogenic mesoderm come together in thoracic region
- right and left endocardial tubes fuse to form primary heart tube, anterior to gut tube
- myocardium invests cardiac jelly and the endocardial heart tube
What are the different parts of the heart tube from top to bottom?
- 1st aortic arch coming off aortic sac
- bulbus cordia
- primordial ventricle
- primordial atrium
- sinus venosus (where vitelline vein, umbilical vein and cardinal vein come off)
What do vitelline veins drain?
yolk sac
What do cardinal veins drain (x2)?
trunk and head region
What are the 2 parts of the bulbus cordis?
- conus cordis: proximal outflow tract to aorta
- truncus arteriosus: distal outflow tract to pulmonary trunk
Describe the looping and folding of the heart tube
- the 2 ends fold towards each other and to the right
- pushing the apex of the loop to the left
- and rotating slightly so that the right side of the heart tends to be more anterior
- if the ends fold to the left, the developing heart is pushed to the right
- the developing heart pushes into the pericardial sac and the ventricles start to trabeculate
Describe the layers of the lumen of the heart tube
- called common AV canal
- surrounded by dense mesenchymal tissue called cardiac jelly
- produced and replaced by myocardium
- myocardium derived from a mass of splanchnic mesoderm
Explain how the valves form
- mitral and tricuspid: endocardial cushion growth and cavitation to form papillary muscles and chordae tendineae
- pulmonary and aortic: hollowing og endocardial tubercles
Explain the formation of the interventricular septum
- while AV canal is formed, IV septum grows towards the endocardial cushion between right and left AV canals
- doesn’t extend all the way to the endocardial cushion
- extension of endocardial cushion that fills the gap forms membranous part of IV septum
- full formation of IV septum separates the primordial ventricle to become left ventricle from the bulbus cordis which will become right ventricle
Explain how the IA septum begins to form
- septum primum starts to grow inferiorly from the roof towards the endocardial cushion
- forms interatrial septum that separates left and right atria
- to allow blood to circulate, ostium primum forms to allow flow between atrias
Explain the final division of the atria
- before septum primum completely builds IA septum, a second hole appears high on it called ostium secundum
- new septum grows down from roof on right side of septum primum called septum secundum which is the wall of the sinus venosus that invaginates into right side of primordial atria
- once IA septum is done the primordial atria is separated into left and right atria
- foramen ovale provides the connection between them
What does the left and right atria receive after division?
- left atrium receives pulmonary veins
- right atrium receives sinus venosus which differentiates to SVC and IVC