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Examinations of the mechanical aspects of the gastrointestinal function discussed here represent the biophysical fragment of its motor activity. Their purpose is to obtain further characteristics of gastrointestinal smooth muscle layer properties and contractions and an analysis of the relationships between contraction and effect of contraction. Much effort in these studies will still be required because of the complexity of motor events and the multiplicity of the factors affecting these events. Several theoretical and practical, in vivo and in vitro methods were utilized in these investigations and the results of classical methods of gastrointestinal motility examinations have been useful in the characterization of mechanical properties of the gastrointestinal smooth muscle. The application of computer models allows for simulations of motor activity in the given conditions, for evaluation of contractile effect and for prediction of the given motor effect in the considered physiological or pathological situation. These examinations are still not developed in veterinary medicine and their greater usefulness in the veterinary clinics is mostly dependent on the progress in the diagnosis of gastrointestinal motor disturbances.
Bile acids exhibit detergent properties. Their influence on various types of cells in the gastrointestinal wall, including smooth muscle cell, is substantial. They are present in the intestinal lumen and circulation as conjugated or deconjugated salts. In studies in vitro they cause smooth muscle relaxations. Their effects in vivo can be due to their direct action on the smooth muscles or they act indirectly: the action can be mediated by the nervous system and gut hormone release. When the gastrointestinal mucosa is exposed to bile or bile acids the frequency of gastric contractions increases and the activity front of the migrating motor complex (MMC) is initiated. Bile acids exert a stronger effect than the entire bile. The type and amount of bile acids can also be important. The intraarterial route of bile acid administration appears to be more efficient than intraluminal route. Bile diversion from the duodenum induces contrary effects, i.e. a relaxing effect in the stomach and irregular motor activity in the small bowel or prolonged phase 2 MMC have been observed. These effects are apparently due to the interaction of bile acids with muscarinic receptors and mediated by motilin and cholecystokinin, two gut hormones the release of which is strongly influenced by luminal bile acids.
Vomiting syndrome comprises three main components that can also occur separately nausea, retching and vomiting. Currently there is no doubt that multiple changes in gastrointestinal motility occur during the vomiting process. Little is known about motor phenomena during nausea. Distention of the gastrointestinal lumen, antral tachygastria, tonic contractions of glottis and cervical esophagus as well the relaxation of cardia and proximal stomach are the most common alterations. During retching a giant retrograde contraction travels from the jejunum toward the gastric antrum and is associated with slow wave disturbances. Gastric content is expelled to the distended esophagus and then is returned back to the stomach. In the course of vomiting gastric content is expelled outside as a consequence of the relaxation and then contraction of the esophagus. Ejection of gastric content is mainly due to rapid and strong contractions of the abdominal muscle and the diaphragm. Some changes in colon and gallbladder motility may accompany vomiting.
The aim of study was to evaluate the participation of central κ-opioidergic receptors in the modulatory/ inhibitory effect of compound U 50,488H, a highly selective -opioid receptor agonist, on the spike burst activity of the rumen, reticulum and antrum prior to and 10 min after a one-minute i.c.v. infusion of norbinaltorphimine, a competitive κ-opioid receptor antagonist, in conscious sheep. U 50,488H was infused i.c.v. at doses of 0.1, 0.25 and 1.0 µg·kg⁻¹ b.w., norbinaltorphimine at doses 10 times higher. All the doses of U 50,488H infused i.c.v. nonsignificantly changed myoelectrical activity of the wall of the rumen, reticulum and antrum. The effects of U 50,488H were not changed by norbinaltorphimine previously infused at doses of 1.0, 2.5 and 10.0 µg·kg⁻¹ b.w. (i.e. at doses 10 times higher than U 50,488H). The results obtained indicate that central κ-opioid receptors did not participate in any action on myoelectrical activity of forestomachs and antrum in sheep.
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