title: Nucleolar organizer regions (NORs). Their significance in the determination of the origin of the lymphoid vessels.
abstract: OBJECTIVE
  The aim of this study is the evaluation of the cellular activity of the embryonal mesenchyme in order to investigate if the primitive lymph vessels are derived from clefts of the mesenchyme or from capillary offshoots from the endothelium of the veins. For this reason we applied the quantitative estimation of nucleolar organizer regions (NORs) in the endothelial cells of the lymph and blood vessels, as well as in the mesenchymal cells that surround these vessels.
  
  
  METHODS
  Our material consisted of the histological sections from the proper mesenterium of 30 embryos in different stages of development (10th, 12th, 15th, 20th, 23th and 30th week).
  
  
  RESULTS
  A statistically significant difference in the average AgNORs value in the endothelial (ANOVA, p<0.0001) and the mesenchymal cells (ANOVA, p<0.0001) between lymph vessels, blood vessels at close and blood vessels at distant regions (10th, 12th, 15th week) was found. There was no statistically significant difference of the average AgNORs value in the endothelial (ANOVA, p=0.55) and the mesenchymal cells (ANOVA, p=0.49) between lymph vessels, blood vessels at close and blood vessels at distant regions (20th, 23th, 30th week).
  
  
  CONCLUSIONS
  The above results suggest that the development of the lymph vessels follows that of the blood vessels. Furthermore, the intense protein synthesis that is expressed by means of NORs in the mesenchymal cells surrounding lymph vessels from the 10th to the 15th week of development is an additional proof of the view that the primitive lymph vessels are derived from clefts into the embryonal mesenchyma and not from capillary offshoots of the endothelium of the blood vessels.
authors.affiliation: Department of Histology-Embryology, Democritus University of Thrace, Greece.
authors.forename: N
authors.initials: N
authors.lastname: Papadopoulos
authors.forename: C
authors.initials: C
authors.lastname: Simopoulos
authors.forename: A
authors.initials: A
authors.lastname: Hatzimichael
authors.forename: A
authors.initials: A
authors.lastname: Kotini
authors.forename: D
authors.initials: D
authors.lastname: Tamiolakis
mesh_terms: D005865:Gestational Age; D006801:Humans; D008208:Lymphatic System / Q000196:embryology*; D008648:Mesoderm / Q000648:ultrastructure; D009697:Nucleolus Organizer Region / Q000648:ultrastructure*; D013194:Staining and Labeling