Fasciola hepatica: Stereological analysis of vitelline cell development

Abstract

Cytomorphosis of vitelline cells in Fasciola hepatica has been studied quantitatively by means of a Kontron Videoplan computerized image analyser. The process of vitelline cell development was subdivided into four characteristic phases: the stem cell, the intermediate type 1 cell, the intermediate type 2 cell, and the mature cell. The whole cell and the following constituent organelles, the nucleus, nucleolus, mitochondria, granular endoplasmic reticulum (GER), secretory granules, glycogen, heterophagosomes, and lipid, were analysed at each phase. Results indicated that there was a significant increase in nuclear size between the two intermediate cell stages, and a significant increase in nucleolar size between the stem cell and intermediate type 1 cell; the changes were related to possible gene activation, ribosome production, and cell synthesis required for both cell growth and secretory production. Mitochondria increased in number and showed changes in volume and surface area of whole organelles and their cristae such that these correlated with the energy demands of growth and synthesis. The GER increased its average total volume some 16 times and its average total surface area some 25 times between the stem cell and mature cell stages. Even this increase masked the true extent of membrane production by this system, since membrane was transferred to secretory granules; in reality the GER or GER-derived membranes increased more than 42 times between the stem cell and mature cell stages. Shell globules and glycogen eventually contributed 21 and 20%, respectively, to cytoplasmic volume, while heterophagosomes contributed 14% and lipid only 3%. Residual cytoplasm was shown to be an important component in cytomorphosis, comprising never less than 40% of the total cytoplasmic volume and it was shown to increase prior to or parallel with the development and expansion of other systems.