The ascidian pyloric gland : aspects of its form and function in Clavelina huntsmani Van Name, 1931, Corella inflata Huntsman, 1912, and Styela gibbsii (Stimpson, 1864)
| dc.contributor.author | Gowan, Richard Frederick | en_US |
| dc.date.accessioned | 2024-08-13T22:55:58Z | |
| dc.date.available | 2024-08-13T22:55:58Z | |
| dc.date.copyright | 1986 | en_US |
| dc.date.issued | 1986 | |
| dc.degree.department | Department of Biology | |
| dc.degree.level | Master of Science M.Sc. | en |
| dc.description.abstract | The ascidian pyloric gland is an enigmatic organ for which a number of functions have been suggested including excretion, osmoregulation, digestion and glycogen storage. This study used light and electron microscopy to study pyloric gland structure, autoradiography to examine C-1-glucose uptake along the gastrointestinal tract, and light and electron microscopy to examine starvation response. 1.) The pyloric gland has a variable number of ducts leaving the stomach which branch into smaller tubules. The tubules cover all or most of the gastrointestinal tract and near the mid-intestinal epithelium they terminate as large dilated pyloric ampullae. 2.) The pyloric gland consists of a single-layered epithelium arranged around a central lumen. Within the pyloric cells, particularly the pyloric ampullae, a cytonuclear cycle occurs which results in the release of glycogen-rich PAS positive material into the gland lumen. 3.) In the solitary ascidians which were studied, starvation results in a marked decrease in the number of pyloric cells releasing contents into the pyloric lumen, as well as a drastic decrease in the amount of PAS positive glycogen-rich material within the pyloric cells. 4.) With starvation, many of the pyloric cells of Styela gibbsii release their contents into the surrounding haemocoel following degeneration of the basal lamina of connective tissue which surrounds the gland. 5.) In Clavelina huntsman! the release of PAS positive material by the pyloric cells is maintained up to the point of starvation-induced zooid regression. 6.) Results concerning the uptake of C-1-glucose by Corella inflata indicate that the stomach and mid-intestinal epithelium have absorptive functions. The post-intestinal epithelium is non-absorptive and glucose diffuses into the haemocoel through the branchial basket and the esophagus. 7.) C-1-glucose accumulates within the mid-intestinal pyloric ampullae of I• inflata but not within pyloric tubules. The amount of labelled glucose within ampullae of c. inflata (Phlebobranchia) is greater than that noted for an Aplousobranch and less than that seen in Stolidobranchs (Gaill, 1981). I suggest that after prolonged starvation in gibbsii, the basal disintegration of the pyloric cells is a means of releasing nutrients from the pyloric ampullae into the surrounding haemocoel. Since this basal disintegration is associated with a cessation of the pyloric cytonuclear cycle and the absence of PAS positive staining, the nutrient released into the haemocoel is most likely glucose derived from the glycogen found within the cells of fed animals. Basal disintegration of pyloric cells is not seen in C. inflata following starvation due to its short 6 month lifespan which would not normally necessitate a means for maintenance during low nutrient periods (e.g. the winter). However, the release of glycogen via the cytonuclear cycle is shut down to maximize survival. Inc. huntsmani the overwintering strategy involves regression of the zooids and storage of nutrients within the stolonic system. As a result, the pyloric cell basal disintegration is not seen and the cytonuclear cycle is maintained until nutrients become scarce enough to trigger zooid regression. The glycogen-rich PAS positive material, released by the pyloric cytonuclear cycle into the pyloric lumen, is probably released via the main pyloric ducts into the stomach. If this material is required for digestion of the food cord, its absence during starvation (in solitary ascidians) is of little consequence since very little food is present in the stomach. | |
| dc.format.extent | 152 pages | |
| dc.identifier.uri | https://hdl.handle.net/1828/17936 | |
| dc.rights | Available to the World Wide Web | en_US |
| dc.title | The ascidian pyloric gland : aspects of its form and function in Clavelina huntsmani Van Name, 1931, Corella inflata Huntsman, 1912, and Styela gibbsii (Stimpson, 1864) | en_US |
| dc.type | Thesis | en_US |
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