Heart

Heart

1. during gastrulation

   • progenitor heart cells
     • migrate through primitive streak
       • forms Primary Heart Field (PHF)
         • horseshoe shaped
         • 16-18 days
           • cardiogenic field is patterned
             • 5HT establishes laterality
         • myoblasts
         • blood islands
         • secondary heart field (22-28 days)
           • contributes to outflow tract

2. during lateral body folding

   • brings heart cells together
     • at midline

3. fusion produces single tube

   • aortic pole
     • sprouts aortic arch vessels
       • from (aortic) outflow region
     • caudal
   • venous pole
     • remains paired
     • anchored in septum transversum
     • cranial

4. 28 days

   • early embryonic blood vessels
   • formation of aortic arches
     • each pharyngeal arch gets an aortic arch
     • humans don't have 5th arch

5. 18-22 days

   • cranial folding
     • brings heart to primitive thoracic region
       • heart repositioned by
         • overgrowth of neural folds
         • ventral body folding

6. cardiac looping creates typical shape (4.5 weeks

   • bulbus cordis
     • travels down
       • creates bulboventricular sulcus between it and ventricle
   • left atrium
     • travels up
   • readies heart to differentiate chambers
     • molecular regulation
       • left ventricle
         • HAND1
           • NKX2.5 regulates
       • right ventricle
         • HAND2
           • NKX2.5 regulates
   • atrium
     • pushed behind
   • ventricles
     • come forward
   • veins
     • shift right
   • arteries
     • shift left

7. definitive atria form

   • as venous blood flows to right
     • right atrium
       • incorporation of right horn of sinus venosus
     • left atrium
       • incorporation of pulmonary vein
   • 5 weeks
     • formation of endocardial cushions
       • cells derived from
         • endocarium (AV canal)
         • neural crest (outflow tract
       • abnormalities
         • Ebstein Anomaly
           • endocardial cushion pushed too far down
             • valve formed too low
         • DiGeorge Anomaly
           • associated with neural crest cells
         • outflow tract defects
           • neural crest cells did not migrate

8. sinus venosus

   • right horn
     • right atrium
   • left horn
     • coronary sinus
     • oblique vein of left atrium

9. 30-40 days

   • atrial and ventricular septa formation
     • atrial septal defects
       • absence of
         • septum primum
           • apoptosis
         • septum secundum
           • failure to form
     • ventricular septal defects
       • 20% membranous
       • 80% muscular