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Results for “Digestive System Physiological Phenomena”

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At least 199 records · Page 11Linked to original sources
PubMed2000

Application of an object-oriented programming paradigm in three-dimensional computer modeling of mechanically active gastrointestinal tissues.

The aim of this study was to develop a novel three-dimensional (3-D) object-oriented modeling approach incorporating knowledge of the anatomy, electrophysiology, and mechanics of externally stimulated excitable gastrointestinal (GI) tissues and emphasizing the "stimulus-response" principle of extracting the modeling parameters. The modeling method used clusters of class hierarchies representing GI tissues from three perspectives: 1) anatomical; 2) electrophysiological; and 3) mechanical. We elaborated on the first four phases of the object-oriented system development life-cycle: 1) analysis; 2) design; 3) implementation; and 4) testing. Generalized cylinders were used for the implementation of 3-D tissue objects modeling the cecum, the descending colon, and the colonic circular smooth muscle tissue. The model was tested using external neural electrical tissue excitation of the descending colon with virtual implanted electrodes and the stimulating current density distributions over the modeled surfaces were calculated. Finally, the tissue deformations invoked by electrical stimulation were estimated and represented by a mesh-surface visualization technique.

Biomechanical Phenomena↗
PubMed1991

Phasic and tonic contraction processes in the gastrointestinal tract.

The contraction mechanisms of GI smooth muscle can be differentiated with the aid of blockers of the voltage-controlled calcium channel (e.g. nifedipine). On the one hand, nifedipine-sensitive processes produce predominantly phasic-rhythmical contractions which can merge to sustained tonic activation, called 'tetanic tone', and which are combined with spike discharges and calcium influx. On the other hand, nifedipine-resistant and electrically silent processes produce a 'specific tone'. The cooperation of both processes in one and the same cell leads to a great diversity of patterns of smooth muscle activity. 'Specific tone' dominates in regions with reservoir function and contributes significantly to the contractions of GI sphincters, with great differences between sphincter types, the various species, and, in man, also between individuals.

Acetylcholine↗
PubMed2001

Sloth biology: an update on their physiological ecology, behavior and role as vectors of arthropods and arboviruses.

This is a review of the research undertaken since 1971 on the behavior and physiological ecology of sloths. The animals exhibit numerous fascinating features. Sloth hair is extremely specialized for a wet tropical environment and contains symbiotic algae. Activity shows circadian and seasonal variation. Nutrients derived from the food, particularly in Bradypus, only barely match the requirements for energy expenditure. Sloths are hosts to a fascinating array of commensal and parasitic arthropods and are carriers of various arthropod-borne viruses. Sloths are known reservoirs of the flagellate protozoan which causes leishmaniasis in humans, and may also carry trypanosomes and the protozoan Pneumocystis carinii.

Animal Nutritional Physiological Phenomena↗
PubMed1987

Extrapituitary effects of corticotropin-releasing factor.

Corticotropin-releasing factor (CRF) has been identified in brain regions that participate in the regulation of the autonomic nervous system and behavioral responses. This paper summarizes the central nervous system as well as the peripheral effects of CRF that are different from those on the anterior pituitary. CRF acts within the brain to increase plasma concentrations of adrenaline and noradrenaline resulting in increased plasma concentrations of glucagon and in hyperglycemia. In the dog, CRF also acts within the brain to increase plasma concentrations of vasopressin. The intracerebroventricular administration of CRF results in a decrease of gastric acid secretion stimulated exogenously by pentagastrin and 2-deoxy-D-glucose or stimulated endogenously by a protein meal. CRF also acts within the brain to decrease gastric emptying and small intestinal transit but to increase large bowel transit and fecal excretions. The central administration of CRF produces hypertension, tachycardia and an elevated oxygen consumption. The effects of CRF on behavior are numerous. CRF induces a reduction in food intake, increases grooming behavior, locomotor activity, vocalization and induces an aroused state but decreases sexual receptivity. Intravenous administration of CRF decreases gastric acid secretion, gastric emptying and blood pressure but increases heart rate, plasma vasopressin concentrations, mesenteric and aortic blood flow, venous return to the heart and pancreatic bicarbonate and protein secretions. The physiological significance of these peripheral actions of CRF on various organ systems is not known.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

The wave phenomena in smooth muscle syncytia.

Based on the concept of a functional unit, a mathematical model of a segment of the gut is developed. The model comprises real anatomical, histomorphological, physiological, and pharmacological information on the function of the organ. Numerical investigation into the dynamics of the electromechanical wave phenomenon reveals the fundamental principles of wave initiation, formation, and propagation along electrically anisotropic longitudinal and isotropic circular smooth muscle syncytia. A pattern of self-sustained electrical activity with the formation of spiral waves is discovered in the longitudinal syncytia and is attributed to the change in conductivity in the syncytia as a result of mechanical deformation of smooth muscle fibers. The model adequately predicts the effects of pharmacological interventions on the dynamics of myoelectrical activity. Although no direct experimental comparison to the theoretical findings is possible at this stage, the proposed mathematical model provides new insight onto the basics of physiological processes--slow wave activity, electromechanical conjugation, etc.--and a clinical entity--gastrointestinal dysrhythmias.

Algorithms↗
PubMed2001

Quality assurance criteria for probiotic bacteria.

Acid and bile stability and intestinal mucosal adhesion properties are among the criteria used to select probiotic microbes. The quality control of probiotic cultures in foods traditionally has relied solely on tests to ensure that an adequate number of viable bacteria are present in the products throughout their shelf lives. Viability is an important factor, but not the only criterion for quality assurance. To be effective, probiotic strains must retain the functional health characteristics for which they were originally selected. Such characteristics include the ability to survive transit through the stomach and small intestine and to colonize the human gastrointestinal tract. In vitro test protocols can be readily adopted to examine the maintenance of a strain's ability to tolerate acidic conditions, survive and grow in the presence of bile, and metabolize selective substrates. Molecular techniques are also available to examine strain stability. Adhesion characterization may be an important quality-control method for assessing gut barrier effects. Adhesion has been related to shortening the duration of diarrhea, immunogenic effects, competitive exclusion, and other health effects. Adhesion properties should be carefully monitored, including adhesion to intestinal cells (eg, Caco-2) and human intestinal mucus. This article outlines the types of in vitro testing that can be used to ensure quality control of functional probiotic strains.

Bacteria↗
PubMed1991

Neonatal gastrointestinal growth and function: are they regulated by composition of feeds?

The effects of natural suckling versus a cow's milk formula on gastrointestinal growth and mucosal function were measured in newborn guinea pigs during the first 8 days of postnatal life. Comparable growth was achieved between the two groups. Both feeds appeared to be a stimulus for the growth of the gastrointestinal tract and expression of disaccharidases, but not for mucosal growth. Formula feeding was associated with a diminished rate of lactase expression and an enhanced rate of maltase and sucrase expression suggesting that the effect of natural suckling is regulatory, acting to delay expression of an inherent ontogenic programme uncovered by formula feeding. These finding in the precocial guinea pig contrast with those in the altricial rat, and have implications for our understanding of the regulation of gastrointestinal development and effects of formula feeds, in other species, including man.

Animal Nutritional Physiological Phenomena↗
PubMed1995

Effect of early nutrient restriction on broiler chickens. 1. Performance and development of the gastrointestinal tract.

An experiment was conducted to determine the effects of early nutrient restriction on performance and development of the gastrointestinal tract of broiler chickens. Four hundred male broiler (Ross x Ross) chicks raised in floor pens were assigned to two treatment groups. One group was given ad libitum access to feed from 1 to 48 d of age. The second group was feed restricted from 7 to 14 d of age to an energy intake of 1.5 x BW.67 kcal ME/d and then given ad libitum access to feed from 14 to 48 d. Body weight and feed intake were determined weekly. At 49 d of age, birds were processed for carcass yield, abdominal fat pad measurement, and body composition analysis. Broilers were also sampled at 7, 14, 21, and 41 d of age for proventriculus, gizzard, small intestine (duodenum, jejunum, and ileum), pancreas, and liver weights and for intestinal length measurements. Total DNA, protein:DNA, and RNA:DNA ratios of livers and jejuna were determined as indexes of changes in cell size and number. Feed-restricted broilers failed to catch up to the Control birds in BW at 48 d of age but were superior (P < .01) in overall feed efficiency. No treatment effects were observed on breast meat yields or abdominal fat. Moreover, percentage carcass fat, crude protein, ash, and dry matter were not affected by restricted feeding. Body weight and weights of gastrointestinal organs were reduced (P < .01) by feed restriction at 14 d of age. Restricted feeding, however, did not decrease the relative weights of organs, except for liver. Feed restriction also resulted in a reduction (P < .01) of liver cell number and size and a decrease in jejunum cell number. All organs recovered normal weight on refeeding, and all cellular constituent ratios (e.g., RNA:DNA, RNA:protein, and protein:DNA) returned to normal by 41 d of age. Absolute and relative weights of supply organs (e.g., proventriculus, gizzard, small intestine, liver, and pancreas) were less affected by feed restriction and responded more quickly to refeeding than the whole body.

Animal Nutritional Physiological Phenomena↗
PubMed1982

Food intake after intragastric meals of short-, medium, or long-chain triglyceride.

Food-deprived Sprague-Dawley rats were given equicaloric intragastric infusions of mixed meals consisting largely of short- (SCT), medium- (MCT), or long-chain triglyceride (LCT). When animals were allowed to feed 20 min after infusion, there was an immediate reduction of food intake that was sustained over the 2 hr feeding period. During the first hour of feeding, the SCT, which is digested and absorbed more rapidly than the MCT or the LCT, was more effective per calorie in reducing food intake than these longer-chain triglycerides. However, during the second hour, cumulative intakes after the different triglyceride infusions were not significantly different. Equicaloric infusions of the MCT and the LCT resulted in equivalent reductions of food intake at all times. The satiety effects of these two triglycerides appear to be related to their caloric properties rather than to chain length. Since the LCT reduced food intake before the absorbed fat could have entered the blood to stimulate satiety signals, this satiety effect may be mediated by a gastroenteric signal. None of the triglyceride infusions resulted in a conditioned taste aversion suggesting that food intake was reduced through normal satiety rather than through discomfort.

Animals↗