Sidon E W, Peek W D, Youson J H, Fisher M M
J Anat. 1980 Oct;131(Pt 3):499-517.
The purpose of the present investigation was to describe ultrastructural characteristics of hepatic bile ducts and the gall bladder in larvae of the sea lamprey, Petromyzon marinus, using freeze--fracture replicas as well as ultrathin sections. Comparison of these structures with those of other vertebrates was necessary to provide a basis in future studies for characterization of biliary degeneration during metamorphosis. The bile ducts were composed of a simple cuboidal to columnar epithelium with the cells separated by wide lateral intercellular spaces and containing a prominent brush border. Vacuole-like intracytoplasmic cisternae formed a peripheral network within the cells and were confluent with intercellular spaces at the site of numerous pores in the lateral plasma membranes. The cells were joined apically by well developed zonulae occludentes surmounting zonulae adhaerentes. The zonulae occludentes, as observed in freeze--fracture replicas, appeared as a honeycomb-like meshwork. Frequent gaps in P-face ridges suggested a 'leaky' epithelium. The cytoplasm of bile duct cells contained few organelles except for large numbers of mitochondria; many microfilaments were present. The ultrastructural features of those cells reflected an epithelium specialized for absorption and transport and they were similar to cells of the bile ducts in other vertebrates. The general organization of epithelium in the gall bladder resembled that of bile ducts, but intercellular spaces were narrower, peripheral pores and cisternae were absent laterally, and the brush border was less extensively developed at the apical surface. The cytoplasm also contained large pools of glycogen and numerous microfilaments were situated in the apical ectoplasm. The overall appearance of the gall bladder of lampreys suggested that the epithelium was less specialized compared to the water transporting organs of other vertebrate species.
本研究的目的是利用冷冻蚀刻复型以及超薄切片来描述海七鳃鳗（Petromyzon marinus）幼体肝内胆管和胆囊的超微结构特征。将这些结构与其他脊椎动物的结构进行比较，对于未来研究变态过程中胆管退化的特征提供依据是必要的。胆管由单层立方上皮至柱状上皮组成，细胞被宽阔的细胞间侧向间隙分隔，且含有明显的刷状缘。液泡样的胞质内池在细胞内形成周边网络，并在侧向质膜上众多小孔处与细胞间间隙汇合。细胞顶端通过发育良好的紧密连接连接，紧密连接位于黏着连接之上。在冷冻蚀刻复型中观察到的紧密连接呈现为蜂窝状网络。P面嵴上频繁出现的间隙表明上皮具有“渗漏性”。胆管细胞的细胞质除了大量线粒体外几乎没有细胞器；存在许多微丝。这些细胞的超微结构特征反映了一种专门用于吸收和运输的上皮，并且它们与其他脊椎动物胆管的细胞相似。胆囊上皮的总体组织结构与胆管相似，但细胞间间隙较窄，侧向不存在周边小孔和池，且顶端表面的刷状缘发育程度较低。细胞质中还含有大量糖原池，并且许多微丝位于顶端外质中。七鳃鳗胆囊的整体外观表明，与其他脊椎动物物种的水运输器官相比，其上皮的特化程度较低。
