Lecture 3.1 - Development of the Heart - Early Development PDF

Stages of development: Blastulation (week 1): Stages of development: Gastrulation (week 2): Stages of development: Neurulation (week 3): Development of the heart (week 3): ◦The splanchnic part of the mesoderm gives rise to the heart. ◦Endodermal cells begin to secrete an important...

Stages of development: Blastulation (week 1): Stages of development: Gastrulation (week 2): Stages of development: Neurulation (week 3): Development of the heart (week 3): ◦The splanchnic part of the mesoderm gives rise to the heart. ◦Endodermal cells begin to secrete an important growth factor called vascular endothelial growth factor (VEGF) ‣ VEGF begins to stimulate the splanchnic part of mesoderm ‣ Splanchnic part differentiates and forms structures within it (2x pericardial cavities and 2x heart tubes) ◦The two pericardial cavities and heart tubes fuse together - heart tubes get pushed into the pericardial cavities ◦Dorsal mesocardium - gives the heart tube stability and suspends the heart ◦Heart forms in the head and moves down towards the chest cavity ‣ Mesodermal structure gets pushed down into the chest cavity (pericardial cavity)  The heart tube: ◦AS - aortic sac ◦TA - truncus arteriosus ◦BC - bulbus cordis ◦PV - primitive ventricle ◦PA - primitive atria ◦SV - sinus venosus - 3 inflow tracts (right and left horn, plus the veins) ◦CCV - common cardinal vein ◦UV - umbilical vein ◦VV - vitelline vein ‣ Blood flows from legs to head of the embryo (from SV to AS) Looping of the heart (22nd -23rd day): ◦Looping takes place, and the structures get pushed around - PA gets pushed to back of the heart and SV follows slightly ‣ Causes the atria to take final position above the ventricles ◦Cells from SV migrate and form a layer around the heart - formation of visceral pericardium around the heart ◦Heart starts to beat at day 22 - beating cells are from the SV ◦The pacemaker of the primitive heart tube is located in the caudal portion ◦Sinus venosus assumes the pacemaker's role of the embryonic heart (SA node) - located more to the caudal part of embryo IfteefdKsc_f_ eef eIe_ d tde es The heart tube: ◦AS - aortic sac -> ascending aorta + right brachiocephalic trunk ◦TA - truncus arteriosus -> pulmonary trunk + ascending aorta ◦BC - bulbus cordis -> right ventricle + outflow tracts ◦PV - primitive ventricle -> left ventricle ◦PA - primitive atria -> left atrium + right atrium ‣ Cells outside the heart (cells that form the lung buds) are used to form the tracts (pulmonary veins) going into the left atrium Septation of the heart (~27th day): ◦Neural crest cells migrate and form the endocardial cushions in the heart tube - fuse together and form a septum (septum intermedium) ‣ Separates into the right and left AV canals  Formation of AV valves (week 4): ◦Neural crest cells differentiates and migrates to form a ring-like structure - forms the valves ‣ Forms the Valvular annulus which connects to the valves ◦Chordae tendinae is formed in this process - used to keep valves shut ◦Mitral and Tricuspid valves formed Formation of interatrial septum: ◦Chambers and valves have been made at this point ◦Septum primum is formed from tissue - doesn't touch the septum intermedium yet, and this cavity produced is known as the Ostium Primum ◦Septum primum fuses with the intermedium ◦Another gap forms- ostium secundum ‣ Another tissue known as the septum secundum forms next to the septum primum ◦Foramen Ovale then forms - a form of bypassing the lungs through separation of oxygenated and deoxygenated blood (communication between right and left sides of the heart) Formation of interventricular septum: ◦Another septum develops in the ventricles - muscular portion of interventricular septum ◦Membranous portion of interventricular septum forms, which connects the muscular portion of interventricular septum to the septum intermedium Formation of inflow tracts to right atrium: ◦Sinus venosus (from the side of the left horn) gets absorbed into right atrium ◦All veins in left horn degenerate Essee affecesse scores ◦Remaining left horn becomes coronary sinus in right atrium ◦CCV becomes superior vena cava on the right atrium ◦VV becomes inferior vena cava on right atrium ◦Umbilical vein (UV) degenerates Formation of outflow tracts: ◦Cells migrate and form ridges (Truncal and Bulbar ridges) from neural crest cells ◦The structure twists - aortico-pulmonary septum forms ‣ Forms pulmonary tracts and aorta ◦There is a region above the BC known as the conus cordis, which later forms the semi-lunar valves ◦Once the outflow tracts are formed, the dorsal mesocardium disintegrates and is taken over by the new outflow tracts - leads to formation of transverse and oblique sinus