刊디스토마(clonorchis sinensis)消化管의 微細構造에 關한 電子顯微鏡的 硏究

Abstract

[한글]

[영문]

The ultrastructure of the alimentary tract of digenetic trematoda was investigated by several workers (Gresson and Threadgold, 1959; Senft et al., 1961; Ercoli et al., 1963; Thorsell and Bjorkman, 1965), and they were uncertain about

the mechanisms of absorption of nutrients and excretion employed by trematoda.

Clonorchis sinensis is a common parasite of humans, mainly distributed in South-east Asia and the Far East. However, the mechanisms of absorption of nutrients, and of secretion in the ceca of this worm have not yet been clearly elucidated. This study was undertaken systematically to elucidate the ultrastructure of the alimentary tract of adult C. sinesis and to provide the morphological means of absorption and secretion in the cecum of this worm.

Materials and methods

Rabbits which had previously been infected with metacercariae of C. sinensis from Pseudorasbora parva, were killed by air embolism, and adult worms were removed immediately from the common bile duct of the rabbit, and put into 37℃ physiolgical saline solution. Motile worms were dissected off oral, esophageal, middle and the most caudal part of cecum about 1 by 2mm pieces respectively, and fixed for 1 hour in chilled 1.25% glutaraldehyde buffered to pH 7.2 with sodium cacodylate. The

pieces of worm were then postosmicated for 1 to 2 hours in 2% osmium tetroxide buffered to pH 7.2 with sodium cacodylate. Dehydration of the specimens was followed through ethanol series and propylene oxide. The speciments were embedded in a proportion of 3:1 mixture of Epon 812. Thin sections were cut on a Porter-Blum ultramicrotome with glass or diamond knives, collected on uncoated copper grids, and double stained with aqueous uranyl acetate. The specimens were examined with either Hitachi HS-8 or HU-11 electron microscope.

Results and conclusions

A) Oral sucker and esophageal part:

The wall of oral cavity and esophageal wall consist of surface syncytium basement membrane, loose connective tissue and parenchymal tissue. The apical surface layer is covered by a protoplasmic membrane forming many invaginations. The cytoplasm of the surface syncytium contains numerous mitochondria which have a few cristae, and variable size (0.8∼0.4 μ in diameter).

Another inclusion which appears a very dense electron plate as ovoidal or rod shapes, distributed in it, and the inclusion called a secretion body (dense body). There is no nucleus, endoplasmic reticulum, Golgi complexes, nor ribosomes in the

surface syncytium.

Basement membrane is located beneath the basal protoplasmic membrane of surface layer, and it is deep infolding to cytoplasm of the surface at the part of oral sucker. Loose connective tissue lies below the basement membrane and it embedded muscular bundles. Among this location, there are tube-like or sac-like vesicles which may join the surface syncytium and integumental cell. Integumental cells lie in the parenchyma which is located under muscular bundles. Their nuclei have oval and single nucleolus as well as other masses. Golgi complexes, oval mitochondria, endoplasmic reticulum, free ribosomes and numerous secretion bodies are present around the nuclear membrane.

B) Cecum part:

The cecal wall of C. sinensis consists of a single layer and of protoplasmic projections lining the lumen, a basement membrane, and muscle bundles are embedded in connective tissue. The protoplasmic projection enters freely into the lumen in some cases, forming folds. The projections of extension are about 0.2 μ in width and several microns in length as seen in section, bound by plasma membrane approximately 70 A° in thickness.

The cytoplasm contains numerous arrangements of endoplasmic reticulum, mitochondria, Golgi apparatus and free ribosome. The ovoidal nucleus is enveloped by a typical nuclear membrane, and it contains a nucleolus and varying amounts of chromatin, heterochromatin scattered adjacent to the nuclear membrane, and

homochromatin distributed around the nucleolus. Mitochondria in the enteric cells are relatively small and possess a few cristae. Some differences of ultrastructure are seen on the regional variations in the cecal wall of C. sinensis.

The alimentary tract of C. sinensis was studied with the electron microscope, and morphological differences were revealed on regional variations for both absorption and secretion.

At the level of the oral sucker and the esophagus lining is covered with surface syncytium which contains many mitochondria, secretory bodies and vesicles. The syncytium lies on basement membrane, and under the basement membrane, muscular bundles are embedded in connective tissue. The integumental cell which is located in the parenchyma, contains nucleus, mitochondria, granular endoplasmic reticulum, Golgi complexes and free ribosomes. Also many secretory bodies are seen around the

nucleus and Golgi complex.

At the middle level the cecum consists of a single layer and numerous protoplasmic projections lining the lumen, whereas the most caudal part of the cecum has no protoplasmic pojections, but numerous granular endoplasmic reticulum and ribosomes. The cytoplasm lining the cecum contains nucleolus, swelled endoplasmic reticulum, Golgi complexes, dense secretory body, mitochondria and free ribosomes.