Properties of Electrical Rhythmicity in the Stomach

2003 ◽  
Author(s):  
Kenton M. Sanders ◽  
Tamas Ördög
Keyword(s):  
Membrane Potential ◽  
Plasma Membranes ◽  
Particle Diameter ◽  
Solid Particles ◽  
Slow Waves ◽  
Distal Stomach ◽  
Coupled Cells ◽  
Gastric Peristalsis ◽  
Greater Curvature ◽  
Peristaltic Contractions

Gastric peristaltic contractions are the basis for emptying of solids from the stomach. These events begin in the mid to high corpus region, develop into a ring around the stomach, and spread down the length of the stomach to the pylorus. The pressure wave resulting from gastric peristalsis pushes the contents of the stomach toward the pyloric sphincter, but a nearly simultaneous contraction of the ring of muscle in the pyloric canal and the terminal antrum ultimately forces much of the food in the retrograde direction, toward the body of the stomach. Sheer forces that develop as a result of this forceful retropulsion cause mechanical disruption of solid particles. Repetitive peristaltic contractions (e.g., in the human these events occur about 3 times per minute), over a period of time, reduces ingested foods to small particles. The action of gastric peristalsis in the distal stomach facilitates emptying and the reduced particle diameter aides in chemical digestion of foods in the small intestine. Pathophysiological conditions that disrupt or disorganize gastric peristalsis can impair or delay normal gastric emptying. Gastric peristaltic contractions result from depolarization of the plasma membranes of smooth muscle cells. For many years it has been known that gastric muscles display periodic (or rhythmic) electrical activity in which membrane potential oscillates between negative potentials and more depolarized levels. The oscillations in membrane potential are known as electrical slow waves (see Color Figs. 2.1 and 2.2 in separate color insert). Slow waves are generated within the tunica muscularis of the proximal corpus along the greater curvature of the stomach, and these events spread around the circumference and down the stomach to the pylorus. A greater velocity of propagation around the stomach than down the stomach causes development of a ring of excitation, and this is the electrical basis underlying gastric peristaltic contractions. Studies have shown that electrical slow waves are generated by specialized pacemaker cells, known as interstitial cells of Cajal (ICCs). The main pacemaker ICCs in the stomach form a dense network of electrically coupled cells between the circular and longitudinal muscle layers of the corpus and antrum.

Antral recirculation in the stomach during gastric mixing

2013 ◽  
Vol 304 (5) ◽  
pp. G536-G542 ◽  
Author(s):  
Yohsuke Imai ◽  
Ikuma Kobayashi ◽  
Shunichi Ishida ◽  
Takuji Ishikawa ◽  
Martin Buist ◽  
...  
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Flow Modeling ◽  
Distal Stomach ◽  
Initial Location ◽  
Greater Curvature ◽  
Twisted Shape ◽  
Peristaltic Contractions ◽  
Realistic Geometry

We investigate flow in the stomach during gastric mixing using a numerical simulation with an anatomically realistic geometry and free-surface flow modeling. Because of momentum differences between greater and lesser curvatures during peristaltic contractions, time-averaged recirculation is generated in the antrum, with retropulsive flow away from the pylorus and compensation flow along the greater curvature toward the pylorus. Gastric content in the distal stomach is continuously transported to the distal antrum by the forward flow of antral recirculation, and it is then mixed by the backward retropulsive flow. Hence, the content inside the antral recirculation is well mixed independently of initial location, whereas the content outside the recirculation is poorly mixed. Free-surface modeling enables us to analyze the effects of posture on gastric mixing. In the upright, prone, and right lateral positions, most of the antrum is filled with content, and the content is well mixed by antral recirculation. In contrast, in the supine and left lateral positions, most of the content is located outside antral recirculation, which results in poor mixing. The curved, twisted shape of the stomach substantially supports gastric mixing in fluid mechanical terms.

Experimental Investigation of Convective Melting of Granular Packed Bed Under Microgravity

2000 ◽  
Author(s):  
J. Jiang ◽  
Y. Hao ◽  
Y.-X. Tao
Keyword(s):  
Experimental Investigation ◽  
Average Particle Size ◽  
Particle Diameter ◽  
Vertical Direction ◽  
Packed Bed ◽  
Melting Rate ◽  
Control Flow ◽  
Solid Particles ◽  
Average Particle ◽  
Ice Particles

Abstract To improve the understanding of convective melting of packed solid particles in a fluid, an experimental investigation is conducted to study the melting characteristics of a packed bed by unmasking the buoyancy forces due to the density difference between the melt and solid particles. A close-loop apparatus, named the particle-melting-in-flow (PMF) module, is designed to allow a steady state liquid flow under a specified temperature. The module is on board NASA’s KC-135 reduced gravity aircraft for the experiments. In the test module, water is used as the fluid, and ice particles are fed to the test section at the beginning of the test. As the liquid flows though the bed, the solid grains melt. A perforate plate, through which liquid can flow while the ice particles are retained, bounds the downstream of the packed bed. From the digital video images the local packed bed thickness is measured under control flow rate, and the melting rate is determined. The temperature distribution along the horizontal direction and vertical direction is measured using 19 thermocouples. An infrared camera is mounted to record the local temperature variation between liquid and solid. The melting rates are presented as a function of upstream flow velocity, temperature and initial average particle size of the packed bed. It is found that the melting rate is influenced mainly by the ratio of the Reynolds number (Re, based on the initial particle diameter) to the square of the Froud number (Fr), and me Stefan number (Ste). In general, the dimensionless melting rate decreases as Re/Fr2 increases and increases as Ste increases. With the absence of gravity, i.e., Froud number approaches infinity, a maximum melting rate can be achieved for otherwise the same test conditions. The increase in the melting rate with the increase in Stephan number also becomes more pronounced under the zero gravity condition.

Modeling evaluation on solid-liquid mixing characteristics in a dislocated guide impeller stirred tank

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Deyin Gu ◽  
Fenghui Zhao ◽  
Xingmin Wang ◽  
Zuohua Liu
Keyword(s):  
Power Consumption ◽  
Solid Particle ◽  
Particle Diameter ◽  
Solid Particles ◽  
Stirred Tank ◽  
Mixing Process ◽  
Solid Holdup ◽  
Aperture Ratio ◽  
Liquid Mixing ◽  
Solid Liquid

Abstract The solid-liquid mixing characteristics in a stirred tank with pitched blade impellers, dislocated impellers, and dislocated guide impellers were investigated through using CFD simulation. The effects of impeller speed, impeller type, aperture ratio, aperture length, solid particle diameter and initial solid holdup on the homogeneity degree in the solid-liquid mixing process were investigated. As expected, the solid particle suspension quality was increased with an increase in impeller speed. The dislocated impeller could reduce the accumulation of solid particles and improve the cloud height compared with pitched blade impeller under the same power consumption. The dislocated guide impeller could enhance the solid particles suspension quality on the basis of dislocated impeller, and the optimum aperture ratio and aperture length of dislocated guide impeller were 12.25% and 7 mm, respectively, in the solid-liquid mixing process. Smaller solid particle diameter and lower initial solid holdup led to higher homogeneity degree of solid-liquid mixing system. The dislocated guide impeller could increase solid particle integrated velocity and enhance turbulent intensity of solid-liquid two-phase compared with pitched blade impeller and dislocated impeller under the same power consumption.

Effect of cromakalim and lemakalim on slow waves and membrane currents in colonic smooth muscle

1991 ◽  
Vol 260 (2) ◽  
pp. C375-C382 ◽  
Author(s):  
J. M. Post ◽  
R. J. Stevens ◽  
K. M. Sanders ◽  
J. R. Hume
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Slow Wave ◽  
Outward Current ◽  
Wave Activity ◽  
Slow Waves ◽  
Slow Wave Activity ◽  
Ca Current ◽  
K Current ◽  
Stimulation Of

The effects of cromakalim (BRL 34915) and its optical isomer lemakalim (BRL 38227) were investigated in intact tissue and freshly dispersed circular muscle cells from canine proximal colon. Cromakalim and lemakalim hyperpolarized resting membrane potential, shortened the duration of slow waves by abolishing the plateau phase, and decreased the frequency of slow waves. Glyburide, a K channel blocker, prevented the effect of cromakalim on slow-wave activity. The mechanisms of these alterations in slow-wave activity were studied in isolated myocytes under voltage-clamp conditions. Cromakalim and lemakalim increased the magnitude of a time-independent outward K current, but cromakalim also reduced the peak outward K current. Glyburide inhibited lemakalim stimulation of the time-independent background current. Nisoldipine also reduced the peak outward current, and in the presence of nisoldipine, cromakalim did not affect the peak outward component of current. This suggested that cromakalim may block a Ca-dependent component of the outward current. Lemakalim did not affect the peak outward current. We tested whether the effects of cromakalim on outward current might be indirect due to an effect on inward Ca current. Cromakalim, but not lemakalim, was found to inhibit L-type Ca channels; however, glyburide did not alter cromakalim inhibition of inward Ca current. We conclude that the effects of cromakalim and lemakalim on membrane potential and slow waves in colonic smooth muscle appear to result primarily from stimulation of a time-independent background K conductance. The effects of these compounds on channel activity may explain the inhibitory effect of these compounds on contractile activity.

scholarly journals Numerical Simulations and Experiments of Ignition of Solid Particles in a Laminar Burner: Effects of Slip Velocity and Particle Swelling

2020 ◽  
Author(s):  
Antonio Attili ◽  
Pooria Farmand ◽  
Christoph Schumann ◽  
Sima Farazi ◽  
Benjamin Böhm ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ignition Delay ◽  
Delay Time ◽  
Slip Velocity ◽  
Ignition Delay Time ◽  
Flame Structure ◽  
Particle Diameter ◽  
Point Particle ◽  
Solid Particles ◽  
Experimental Measurements

Abstract Ignition and combustion of pulverized solid fuel is investigated in a laminar burner. The two-dimensional OH radical field is measured in the experiments, providing information on the first onset of ignition and a detailed characterization of the flame structure for the single particle. In addition, particle velocity and diameter are tracked in time in the experiments. Simulations are carried out with a Lagrangian point-particle approach fully coupled with an Eulerian solver for the gas-phase, which includes detailed chemistry and transport. The numerical simulation results are compared with the experimental measurements in order to investigate the ignition characteristics. The effect of the slip velocity, i.e. the initial velocity difference between the gas-phase and the particle, is investigated numerically. For increasing slip velocity, the ignition delay time decreases. For large slip velocities, the decrease in ignition delay time is found to saturate to a value which is about 40% smaller than the ignition delay time at zero slip velocity. Performing a simulation neglecting the dependency of the Nusselt number on the slip velocity, it is found that this dependency does not play a role. On the contrary, it is found that the decrease of ignition delay time induced by the slip velocity is due to modifications of the temperature field around the particle. In particular, the low-temperature fluid related to the energy sink due to particle heating is transported away from the particle position when the slip velocity is non-zero; therefore, the particle is exposed to larger temperatures. Finally, the effect of particle swell is investigated using a model for the particle swelling based on the CPD framework. With this model, we observed negligible differences in ignition delay time compared to the case in which swelling is not included. This is related to the negligible swelling predicted by this model before ignition. However, this is inconsistent with the experimental measurements of particle diameter, showing a significant increase of diameter even before ignition. In further simulations, the measured swelling was directly prescribed, using an analytical fit at the given conditions. With this approach, it is found that the inclusion of swelling reduces the ignition delay time by about 20% for small particles while it is negligible for large particles.

Electrical and mechanical interactions between the muscle layers of canine proximal colon

1990 ◽  
Vol 258 (3) ◽  
pp. G484-G491 ◽  
Author(s):  
P. J. Sabourin ◽  
Y. J. Kingma ◽  
K. L. Bowes
Keyword(s):  
Membrane Potential ◽  
Circular Muscle ◽  
Longitudinal Direction ◽  
Proximal Colon ◽  
Slow Waves ◽  
The Other ◽  
Potential Oscillations ◽  
Circular Layer ◽  
Longitudinal Layer ◽  
Membrane Potential Oscillations

Electrical and mechanical interactions between the two smooth muscle layers of canine colon have been studied using a dual sucrose gap apparatus. Muscle samples were dissected into an L-shape, with one leg cut in the circular direction and the other cut in the longitudinal direction. Longitudinal muscle was removed from the circular leg and circular muscle was removed from the longitudinal leg. The bend of the L contained both layers. The activity of the two layers was studied simultaneously under basal conditions, after stimulation by neostigmine and carbachol, and in the presence of tetrodotoxin. Interactions were more common after stimulation and were marked by modification of one layer's mechanical and electrical activity during increased activity in the other layer. Two patterns were commonly observed. First, during a burst of membrane potential oscillations and spike potentials in the longitudinal layer, slow waves in the circular layer developed spike potentials and some slow waves were also prolonged. Second, during a slow-wave cycle in the circular layer, the amplitude of membrane potential oscillations in the longitudinal layer was increased with an associated increase in the incidence of spike potentials. These interactions were associated with contractions of increased strength, which were similar in both layers. All interactions continued after nerve-conduction blockade by tetrodotoxin.

scholarly journals Prostaglandin regulation of gastric slow waves and peristalsis

2009 ◽  
Vol 296 (6) ◽  
pp. G1180-G1190 ◽  
Author(s):  
Abigail S. Forrest ◽  
Grant W. Hennig ◽  
Sari Jokela-Willis ◽  
Chong Doo Park ◽  
Kenton M. Sanders
Keyword(s):  
Slow Wave ◽  
Slow Waves ◽  
Wave Frequency ◽  
Functional Coupling ◽  
Receptor Agonists ◽  
Gastric Corpus ◽  
Gastric Peristalsis ◽  
Chronotropic Effects ◽  
Cells Of Cajal ◽  
The Impact

Gastric emptying depends on functional coupling of slow waves between the corpus and antrum, to allow slow waves initiated in the gastric corpus to propagate to the pyloric sphincter and generate gastric peristalsis. Functional coupling depends on a frequency gradient where slow waves are generated at higher frequency in the corpus and drive the activity of distal pacemakers. Simultaneous intracellular recording from corpus and antrum was used to characterize the effects of PGE2 on slow waves in the murine stomach. PGE2 increased slow-wave frequency, and this effect was mimicked by EP3, but not by EP2, receptor agonists. Chronotropic effects were due to EP3 receptors expressed by intramuscular interstitial cells of Cajal because these effects were not observed in W/W V mice. Although the integrated chronotropic effects of EP3 receptor agonists were deduced from electrophysiological experiments, no clear evidence of functional uncoupling was observed with two-point electrical recording. Gastric peristalsis was also monitored by video imaging and spatiotemporal maps to study the impact of chronotropic agonists on propagating contractions. EP3 receptor agonists increased the frequency of peristaltic contractions and caused ectopic sites of origin and collisions of peristaltic waves. The impact of selective regional application of chronotropic agonists was investigated by use of a partitioned bath. Antral slow waves followed enhanced frequencies induced by stimulation of the corpus, and corpus slow waves followed when slow-wave frequency was elevated in the antrum. This demonstrated reversal of slow-wave propagation with selective antral chronotropic stimulation. These studies demonstrate the impact of chronotropic agonists on regional intrinsic pacemaker frequency and integrated gastric peristalsis.

Parametric Studies of a Spectrally Selective, Two-Layered, Porous, Volumetric Solar Collector

1992 ◽  
Vol 114 (3) ◽  
pp. 150-156 ◽  
Author(s):  
D. A. Kaminski ◽  
S. Kar
Keyword(s):  
Solar Collector ◽  
Cone Angle ◽  
Particle Diameter ◽  
Solid Particles ◽  
Solar Flux ◽  
Radiative Properties ◽  
Critical Parameters ◽  
Fluid Temperature ◽  
Spectrally Selective ◽  
Parametric Studies

A porous, packed bed, volumetric solar collector consisting of two dissimilar layers of spherical beads is numerically modeled. The bed is irradiated on the top surface by concentrated solar flux isotropic within a known cone angle. A gas stream perfusing the bed is heated by convection with the solid particles. The equation of radiative transfer, which accounts for absorption, emission, and linearly anisotropic scattering in the bed, is simplified by employing the P1 differential approximation. The bed materials are spectrally selective in the solar and infrared wavelengths. Sensitivity studies are used to identify the critical input parameters of the system, and a baseline configuration, which incorporates the key requirements of an efficient solar collector, is adopted. Parametric studies are conducted on the mass flow rate, incident solar flux, top layer porosity, solar absorptivity, particle diameter, and degree of back scatter. Tailoring of the particle and fluid temperature profiles and enhancing the efficiency of the collector by an appropriate selection of these critical parameters is demonstrated. Various high-temperature ceramics with suitable radiative properties are identified and their relative performance in the collector is assessed.

Effects of Ultraviolet Radiation on the Plasma Membranes of Chara corallina. I The Hyperpolarized State

1976 ◽  
Vol 3 (5) ◽  
pp. 677
Author(s):  
C.J Doughty ◽  
A.B Hope
Keyword(s):  
Membrane Potential ◽  
Ultraviolet Radiation ◽  
Ultraviolet Irradiation ◽  
Plasma Membranes ◽  
Membrane Conductance ◽  
Chara Corallina ◽  
Potential Difference ◽  
Electrogenic Pump ◽  
Chloride Permeability ◽  
Membrane Potential Difference

Effects of 254 nm ultraviolet irradiation on the plasmalemma potential difference and conductance in C, corallina have been further analysed. Following an increase in passive chloride permeability, revealed from previous studies, and which is manifested as a depolarization of membrane potential difference and an increase in membrane conductance, a secondary depolarization was prominent at pH 7 and is attributed to u.v.-induced inhibition of an electrogenic pump. The secondary depolarization was usually accompanied by a decrease in membrane conductance. For doses of u.v. of 1400 J m-2, these effects were almost reversible within about 1 h

Vortex Simulation for Behavior of Solid Particles Falling in Air

2011 ◽  
Author(s):  
Hisanori Yagami ◽  
Tomomi Uchiyama
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Air Flow ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Vortex Method ◽  
Solid Particles ◽  
Particle Volume ◽  
Two Phase ◽  
Spherical Region

The behavior of small solid particles falling in an unbounded air is simulated. The particles, initially arranged within a spherical region in a quiescent air, are made to fall, and their fall induces the air flow around them, resulting in the gas-particle two-phase flow. The particle diameter and density are 1 mm and 7.7 kg/m3 respectively. A three-dimensional vortex method proposed by one of the authors is applied. The simulation demonstrates that the particles are accelerated by the induced downward air flow just after the commencement of their fall. It also highlights that the particles are whirled up by a vortex ring produced around the downward air flow after the acceleration. The effect of the particle volume fraction at the commencement of the fall is also explored.

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