CVS Embryo

• Cardiogenic fields

  Progenitor heart cells (PGHC) lie in the epiblast, cranial to the primitive streak

  • They migrate through the streak to the splanchnic layer of lateral plate mesoderm to form a horseshoe-shaped cluster of cells called the primary heart field (PHF)
• Formation of heart tube

  1. Angioblast cords canalyze to form thin walled endocardial heart tubes

  2. Ventral part of horseshoe plexus forms the cardiogenic region, and the dorsal part forms the dorsal aortae

  3. Intraembryonic cavity over the cardiogenic region develops into the pericardial cavity
• Lateral and cranial folding

  1. Lateral folding brings dorsal aortae (a pair of longitudinal vessels) to midline and heart tubes to fuse to form the single tubular heart

  2. Cranial folding moves the cardiogenic area ventrally and caudally, causing the heart tube and pericardial cavity to move to the cervical then to the thorax
• Circulation through the primordial heart

  1. Blood from the sinus venosus enters the primitive atrium, controlled by the sinoatrial valve

  2. Blood then passes through the atrioventricular canal into the primitive ventricle

  3. Ventricle contraction pumps blood through the bulbus cordis and truncus arteriosus into the aortic sac
• Septation of the AV canal

  1. Dorsal and ventral walls of atrioventricular canal are invaded by mesenchymal cells and form endocardial cushions

  2. The endocardial cushions approach each other and fuse, dividing the atrioventricular canal into right and left
• Septation of primordial atrium


  1. Septum primum grows towards the fusing endocardial cushions from the roof of the primordial atrium, partially dividing the atrium into right and left halves

  2. Perforations appear in the central part of the septum primum and coalesce to form the foramen secundum

  3. Septum secundum extends towards the fused endocardial cushions, leaving an oval opening - the foramen ovale
• Septation of primordial ventricle

  A septum grows upward from base of ventricle towards the intermediate bar, stopping short and leaving a gap - the interventricular foramen
• Septation of the truncus arteriosus

  Endocardial cushions develop in the conotruncal region (conotruncal swellings) and fuse to divide the truncus arteriosus into the aorta and pulmonary trunk
• Nutrition by diffusion can't satisfy embryo need, so progenitor heart cells (PGHC) migrate to form the primary heart field (PHF)
• Cardiac progenitor cells in the mesoderm, lateral from the primitive streak, proceed cranially; rostral to the buccopharyngeal membrane and neural folds. The cells lie in the splanchnic layer of the lateral mesoderm.
• At the cardiogenic area, the underlying pharyngeal endoderm induces the cardiogenic progenitor cells to form the cardiac myoblasts

  • Blood islands also appear in the mesoderm, which arrange themselves into 2- longitudinal cellular cords (angioblast cords, by vasculogenesis) - which unite with time and form a horseshoe-shaped endothelial-lined tube surrounded by myoblasts.
  • Pericardial cavity deve. from IE cavity over cardiogenic area
• Formation of the heart tube

  • The heart tube remains attached dorsally to the body wall, suspended in pericardial cavity by the dorsal mesocardium
  • The DM disappears later forming the transverse pericardial sinus.
  • The transverse pericardial sinus allows a surgeon to isolate the pulmonary trunk and ascending aorta
• Formation of the heart tube

  • All the heart layers are derived from the splanchnic mesoderm around the heart tube, except part of the epicardium, which is derived from mesothelial cells on the surface of the septum transversum
• The endothelial tube becomes the internal endothelial lining of heart, the Endocardium
• The primordium of myocardium (myoblast) becomes the muscular wall of heart, the Myocardium
• The visceral pericardium, or Epicardium is derived from mesothelial cells and lines the pericardial cavity
• The Truncus Arteriosus is continuous cranially with the aortic sac from which the aortic arches arise
• The Sinus Venosus receives the umbilical, vitelline and common cardinal veins from the chorion, yolk sac and embryo respectively

  
• The arterial and venous ends of the heart are fixed by the pharyngeal arches and septum transversum respectively
• Degeneration of the central portion of the dorsal mesocardium leaves the primitive heart attached at the outflow and inflow ends, forming the transverse pericardial sinus

  
• The heart grows rapidly, but it is still fixed at both ends so it loops
• The aortic sac distributes blood through the aortic arches in the brachial and pharyngeal arches, and the blood then passes into the dorsal aorta to the embryo, yolk sac and placenta

  
• The sinus venosus receives venous blood from the right and left sinus horns
• The endocardial cushions develop in the atrioventricular canal (atrioventricular cushions) and in the conotruncal region (conotruncal swellings)
• The endocardial cushions assist in the formation of the atrial and ventricular septa, the atrioventricular canals and valves, and the aortic and pulmonary channels
• The septum primum and septum secundum forms an incomplete partition, that serves like a valve of the foramen ovale
• After birth the foramen ovale normally closes as the septum primum fuses with septum secundum, and the interatrial septum becomes a complete partition
• Septation of the primordial ventricle

  1. A septum grows upward from base of ventricle towards the intermediate bar (IB), stops short of IB, leaving a gap between IB and PM→IV-foramen

  2. IV-foramen closed - by growth of pars membranacae (PMm) of IVS

  
• Pars membranacea of IVS

  Formed from tissues of the fused endocardial cushions, with contributions from the anterior and posterior truncal ridges which divide the common ventricle into right and left ventricles

  
• Septation of truncus arteriosus

  1. Neural crest cells (pharyngeal arches 4 and 6) migrate →truncus arterosus & bulbus cordis, transform into mesenchymal tissue that proliferates

  2. The bulbar and truncal ridges undergo a 180 degree spiralling; this results in the formation of a spiral aorticopulmonary septum when ridges fuse

  3. The septum divides the bulbus cordis and truncus arteriosus into two arterial channels, the aorta and pulmonary trunk

  4. Because of the spiraling of the aorticopulmonary septum, the pulmonary trunk twists around the ascending aorta

  5. The bulbus cordis is incorporated into the walls of the definitive ventricles
• Fate of sinus venosus

  1. Initially the sinus venosus collects blood from paired vitelline veins (vv) and umbilical veins (uv) , then later from common cardinal veins (ccv) superiorly

  2. Absorption of the sinous venosus into the right atrium starts with a deep groove - at the left sino-atrial junction

  3. As the gut tube develops, the vitelline veins are displaced laterally. Splitting the sinous venosus into left and right horns

  4. As the body of the sinus venosus is absorbed into the right atrium, rt and lf venous valves- fuse forming the septum spurium

  5. The rt sinus horn - incorporated into wall of rt atrium

  6. The lf venous valve & septum spurium fuse with developing atrial septum

  7. Sup part rt vv - thickens- form crista terminalis, inf part forms- Vivc & vcs
• Crista terminalis


  Smooth muscular ridge in the superior aspect of the right atrium, formed following resorption of the right valve of the sinus venosus. It represents the junction between the sinus venarum, the "smooth" portion of the right atrium derived from the embryologic sinus venosus, and the heavily trabeculated right atrial appendage
• Absorption of pulmonary vein into the left atrium


  1. A single pulmonary vein is absorbed into the left atrium, creating a smooth surface

  2. Further absorption of the pulmonary vein results in the formation of four openings in the posterior wall of the left atrium

  3. The left common cardinal vein forms the oblique vein (ov) of the left atrium and the remnant of the left horn becomes the coronary sinus (cs)
• Atrial septal defects (ASDs)


  Morphologic defects of the interatrial septum that directly communicate the right and left atria
• Types of ASDs


  • Ostium primum ASD
  • Endocardial cushion defects
  • Ostium secundum ASD
• Premature closing of foramen ovale


  Closure of foramen ovale during pre-natal life, resulting in hypertrophy of the right side of the heart and underdevelopment of the left side of the heart

  
• Common atrium


  Caused by complete failure of septum primum and septum secundum to develop
• Types of Ostium Secundum ASDs


  • Occur in the area of the fossa ovalis
  • Include defects of the septum primum and septum secundum
• Patent foramen ovale (PFO)/Ostium Primum Atrial Septal Defects


  Results from abnormal resorption of septum primum during septation, if resorption occurs in abnormal location, the septum primum becomes fenestrated or netlike
• Ostium Secundum Atrial Septal Defects

  Larger than PFO, may occur because of a combination of excessive resorption of the septum primum and a large foramen ovale- direct communication between the atria