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Studies on gut ultrastructure and digestive physiology in Rhabdias bufonis and R. sphaerocephala (Nematoda: Rhabditida)
- J. Barry Colam
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- Journal:
- Parasitology / Volume 62 / Issue 2 / April 1971
- Published online by Cambridge University Press:
- 06 April 2009, pp. 247-258
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- Article
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Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in the parasitic nematodes Rhabdias bufonis (Schrank, 1788) and R. sphaerocephala (Goodey, 1924). Both species are parasitic in the lungs of their amphibian hosts and feed entirely upon blood drawn from the lung capillaries.
Three gland cells are present in the oesophagus, one in each sector. The two subventral ducts open, by way of ampullae, into the lumen of the oesophagus about a quarter of its length from the anterior end. The dorsal gland opens similarly into the base of the buccal capsule. It is suggested that the glands produce a B-esterase, in an histochemically inactive form in situ, which is responsible for haemolysis and the bulk of extracellular digestion. Only one cell type is present in the intestine and this is entirely absorptive in function.
The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion involving the B-esterase and acid phosphatase which are present in association with the microvilli. Haematin results from this process and is precipitated in the gut lumen. A smaller proportion of haemoglobin is taken up by the gut cells and is broken down intracellularly by lysosomes, originating in Golgi in the basal gastrodermis. These show endopeptidase activity and later acid phosphatase in some of the bodies of the lysosomal sequence and only at the light microscope level. The iron-containing pigment haemosiderin resulting from digestion is retained in the lysosome residues and forms the pigment granules in the gastrodermis. The products of extracellular digestion absorbed by the gastrodermis are synthetized into lipid by a lipase, probably produced by GER.
This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.
Studies on gut ultrastructure and digestive physiology in Cyathostoma lari (Nematoda: Strongylida)
- J. Barry Colam
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- Journal:
- Parasitology / Volume 62 / Issue 2 / April 1971
- Published online by Cambridge University Press:
- 06 April 2009, pp. 273-283
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Histological, histochemical and ultrastructural methods have been used to study the gut structure and digestive physiology in the parasitic nematode Cyathostomalari E. Banchard, 1849. The nematode is parasitic in the orbito-nasal sinuses of its host and feeds exclusively upon blood.
Three gland cells are present in the oesophagus, one in each sector. The two subventral gland ducts open into the lumen of the oesophagus at the level of the nerve ring, and the dorsal gland duct into the base of the buccal capsule. It is suggested that the latter gland may produce an anticoagulin, histolytic and/or haemolytic secretions, histochemically-inactive in situ. The intestine is syncytial, with no differentiation into secretory components, and its distal surface is provided with a prominent brush border of long microvilli.
A non-specific esterase, thought to originate in the oesophageal gland secretions, causes haemolysis of ingested erythrocytes. The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion on the microvilli, initiated by the esterase, and the protein is then further broken down by an exopeptidase of the ‘leucine aminopeptidase’ type, and the products absorbed into the gastrodermis possibly with the aid of an acid phosphatase present on or in the microvilli. An insoluble iron-containing compound, which is not haematin, results from breakdown of the prosthetic group. A smaller proportion of haemoglobin is taken up by the gastrodermis and digested intracellularly by the action of lysosomal hydrolases. An endopeptidase and an acid phosphatase are present in the gastrodermis, possibly in sacs of GER which are suggested to be primary lysosomes and which fuse with the endocytosed heterophagosomes. The insoluble pigment haematin results from digestion within the heterolysosomes, and this gives rise to the iron-containing gastrodermal pigment granules. The products of extracellular digestion are absorbed by the gastrodermis where they are synthetized into lipid by a lipase, which probably resides in whorls of GER.
This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.
Studies on gut ultrastructure and digestive physiology in Cosmocerca ornata (Nematoda: Ascaridida)
- J. Barry Colam
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- Journal:
- Parasitology / Volume 62 / Issue 2 / April 1971
- Published online by Cambridge University Press:
- 06 April 2009, pp. 259-272
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Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in Cosmocerca ornata (Dujardin, 1845). The nematode is parasitic in the small intestine and rectum of Rana temporaria, and feeds solely upon the gut contents of the host, primarily bacteria and cellular debris rather than fluid material.
Only a small buccal capsule is present and no host tissue is ingested. Rigid channels at the tips of the oesophageal radii and a spiral arrangement of the corpus lumen are probably concerned in expressing any fluid in the food while retaining the particulate matter. The latter is then shredded by three large valvular flaps projecting into the lumen of the posterior oesophageal bulb. One gland is present in each sector of the bulb. There is some evidence that two secretions are produced in each subventral sector, an electron-dense one posteriorly which is released into the lumen below the valve flaps, and an electron-lucid one synthesized more anteriorly which is released in the anterior region of the bulb. Only one secretion is produced in the dorsal gland, similar to that in the anterior subventral sector, and which is poured into the lumen of the posterior corpus. The intestine is not differentiated into distinct regions and contains no gland cells. A prominent striated border of microvilli is present, varying from 25 μm in the foregut to 0·5 μm in the hindgut. They have a prominent core composed of minute fibrils and an outer glycocalyx covering.
Digestion is entirely extracellular, bacteria and cellular debris in the ingesta being broken down by a C-esterase present in the oesophageal gland secretions. It is completed by a process of contact digestion with the same enzyme adsorbed on to the glycocalyx. Acid phosphatase, also produced by the oesophageal glands and present on the microvilli, may be concerned in the absorption of the resultant digestion products and any simple solutes in the food made available by host extracellular enzymes. GER and free ribosomes present in the distal regions of the gastrodermis are probably concerned in the assimilation of the absorbed materials into glycogen which is stored in large quantities in the gastrodermis.
This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board.