心臓の仮腱索に関する組織学的・電子顕微鏡的研究

仮腱索はBrowicz1)により,心室内にみられる異常な索状構造物として詳しく報告された.その後,仮腱索は異常な状態におかれたときに生じるものと考えられた13,17).一方, Tawara15)は仮腱索は決して異常なものではなく,ウシやヒツジやイヌでは心室腔内に必ずみられる構造で,その大部分のものに刺激伝導系の,Purkinje線維が関係していることを観察した.さらにHoll4)は,ヒトやウシではその肉眼的解剖においても刺激伝導系の房室系と仮腱索とは深い関連があることをみとめている.現在では,仮腱索は心内膜下のPurkinje細胞の研究材料として検索されていることが多い.そこで,本研究においては,仮腱索がどの動物にも必ず存在するものかどうか,また,どの動物でも必ずPurkinje線維を含んでいるか,さらに仮腱索の中に神経がみられるかどうかということなどを考えて,この仮腱索が機能的にいかなる働きをしているかということを検索した.

False tendons in the heart of several mammals were investigated by light and electron microscopies. False tendons were recognized macroscopically as chordal structures in the inner surface of the ventricles in the cow, pig, monkey, dog and rabbit. The outer surface of false tendons were covered with the same endothelial cell layer as the endocardium. Under the cell layer, there was thick connective tissue whose center was occupied by several bundles of Purkinje fibers. Among Purkinje fibers, thin connective tissue was present, in which small vessels and non-myelinated nerve fibers were observed. False tendons were identified in rats by light microscopy, but they were not found in mice. Purkinje fibers in false tendons varied among species. In artiodactyla, Purkinje fibers were larger and had fewer cell organella than those of other animals. Three types of intercellular junctions, desmosomes, intermediate junctions and gap junctions (nexus), were observed. Nexuses were often observed. Nerve fibers in the false tendons were all nonmyelinated. These nerve fibers only passed through the false tendons, and nerve endings were not found. Nerve cell bodies were not found either. From these results, the roles of false tendons in heart conduction were discussed.