title: On the form problem of embryonic heart loops, its geometrical solutions, and a new biophysical concept of cardiac looping.
abstract: BACKGROUND
  Cardiac looping is an essential process in the morphogenesis of embryonic hearts. Unfortunately, relatively little is known about the form and biophysics of embryonic heart loops. Thompson regarded the form of an object as "a 'diagram of forces' … from it we can … deduce the forces that are acting or have acted upon it." Therefore, the present study was conducted to uncover the best geometrical solution of the form problem of embryonic heart loops. This approach may help to identify the biophysics of cardiac looping.
  
  
  RESULTS
  Analysis of the tendrils of climbing plants disclosed striking resemblance between the configurations of embryonic heart loops and a form motif named helical perversion. Helical perversion occurs in helically wound objects where they connect two helical segments of opposite handedness (two-handed helix). Helical perversion evolves in living and non-living filamentary objects such as the tendrils of climbing plants and helical telephone cords.
  
  
  CONCLUSIONS
  Helical perversion may be the best geometrical solution of the form problem of embryonic heart loops. The dynamics and mechanics of the emergence of helical perversions are relatively well known. The behavior of looping embryonic hearts may be interpreted in light of this knowledge.
authors.affiliation: Department of Anatomy and Embryology, Georg-August-University of Göttingen, Germany. Electronic address: jmaenne@gwdg.de.
authors.forename: Jörg
authors.initials: J
authors.lastname: Männer
mesh_terms: D000818:Animals; D001703:Biophysics; D002642:Chick Embryo; D006321:Heart / Q000033:anatomy & histology / Q000196:embryology* / Q000254:growth & development; D006801:Humans; D007091:Image Processing, Computer-Assisted; D051379:Mice; D008855:Microscopy, Electron, Scanning; D009206:Myocardium / Q000166:cytology / Q000648:ultrastructure; D029598:Passiflora; D018521:Plant Physiological Phenomena; D010944:Plants / Q000033:anatomy & histology; D014982:Xenopus laevis