Neurogastroenterol Motil (2006) 18, 172–183
doi: 10.1111/j.1365-2982.2006.00759.x
REVIEW ARTICLE
Imaging and modelling of digestion in the stomach
and the duodenum
K. SCHULZE
Gastroenterology Research, VAMC and University of Iowa, Iowa City, IA, USA
both in parallel and in sequence. The stomach functions
as a receptacle which retains compact and high-density
food until this is transformed into chyme. The stomach
reduces the size of solid particles and fat globules, and it
adjusts the pH/osmolality, caloric density and viscosity
of liquids. By increasing the surface area on which
digestive secretions interact with substrate, mechanical
digestion potentiates chemical digestion. By controlling
the release of nutrients, the stomach contributes to fuel
homeostasis. Digestion (or trituration) accounts for the
difference in time at which the stomach starts clearing
solids and fats when compared with isotonic liquids.1,2
During this time, the stomach transforms its contents
by dispersing solid particles and fat globules in secretions, and by combining separate phases of aqueous
solutions, fats and solids into the multiphase slurry
called chyme.
The duodenum treats gastric chyme to pancreaticobiliary secretions, and reduces particles to simple
molecules that can cross the epithelial barrier.1–5
Normal intestinal digestion and absorption requires
appropriate digestion in the stomach.2,6,7
Digestion is well studied in terms of the secretion of
gastric acid, bile salts and digestive enzymes; the
enzymatic splitting of proteins, carbohydrates and fats;
and the transport of molecules and ions across the
intestinal epithelium. Similarly, the mechanical functions of the stomach and duodenum are well defined
in terms of viscoelastic properties,8–17 movement
patterns of their walls,18–30 neuronal and electrical
controls,31–48 and the dynamics of gastric emptying.2,6,7,28,49–59 Less well understood are the flow
processes that extract small molecules from complex
foods: secretions have to penetrate food; particles have
to be rendered less compact and suspended in liquid
medium; substrate has to be scattered or drawn into
thin sheets for enzymatic attack; the epithelial
Abstract Gastroduodenal physiology is traditionally
understood in terms of motor-secretory functions and
their electrical, neural and hormonal controls. In
contrast, the fluid-mechanical functions that retain
and disperse particles, expose substrate to enzymes, or
replenish the epithelial boundary with nutrients are
little studied. Current ultrasound and magnetic resonance imaging allows to visualize processes critical
to digestion like mixing, dilution, swelling, dispersion
and elution. Methodological advances in fluid
mechanics allow to numerically analyse the forces
promoting digestion. Pressure and flow fields, the
shear stresses dispersing particles or the effectiveness
of bolus mixing can be computed using information on
boundary movements and on the luminal contents.
These technological advances promise many additional insights into the mechanical processes that
promote digestion and absorption.
Keywords chyme, duodenal bulb, duodenal motility
and absorption, gastric motility and emptying, gastric
secretion, intestinal peristalsis and absorption,
particle
dispersion,
pylorus,
terminal
antral
contraction, trituration.
INTRODUCTION
Man (like most mammalian species) has a single
stomach whose segments perform multiple functions
Address for correspondence
Konrad S. Schulze, MD, Gastroenterology Research,
VAMC and University of Iowa, 4551 JCP, UIHC,
Iowa City, IA 52242, USA.
Tel: 319 356 2793; fax: 319-353-6399;
e-mail: [email protected]
Received: 16 May 2005
Accepted for publication: 15 September 2005
172
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Volume 18, Number 3, March 2006
Mechanics of digestion
boundary has to be replenished with nutrients. These
processes are susceptible to fluid-mechanical analysis.
In the 1990s, James Meyer proposed a fluid-mechanical theory2 to explain the differential emptying of
liquids and solids (gastric sieving). In the decade before,
Christensen and Macagno had pioneered the study of
the gut as a hydraulic system.21,60 They identified
retrograde and radial flow as conducive to mixing and
absorption. A review of gastroduodenal fluid-mechanics is timely because of recent advances in the imaging
of gastric functions and in the computing of complex
flow. It is now possible to construct flow paths for
fluids and particles21,60–62 that cannot be tracked
visually, and to quantify shear stresses or the efficiency
of mixing. Ultrasonography and magnetic resonance
imaging (MRI) can be used to construct intragastric
volumes and volume changes during accommodation
and emptying of the stomach. Both modalities reveal
such physical properties as particle size30,63 and density. Echoplanar imaging has been adapted to monitor
the viscosity of gastric contents as they are diluted by
acid.64 Both imaging modalities have been adapted to
rapid sequence scanning which allows to monitor the
movements of the gastro-duodenal boundaries and of
the luminal contents simultaneously.26,27,29,57,61,63–77
These techniques are known as real time ultrasonography and real time (or echoplanar) MRI.
Here I will focus on recent observations, especially
using real time ultrasonography, magnetic resonance
imaging and flow computations in light of classical
concepts of digestion.8,20,24,78 Originally, I had hoped to
link physical outcomes like particle dispersion with
specific flow events like the retrograde antral jet.
Unfortunately, the importance of individual flow phenomena to digestion remains to be established. The
contribution of pressure forces, shear stresses, flow
reversals and vortical flow has been established under
specific conditions61 but remains to be quantified.62,67
Figure 1 The segments and muscle coat (sling fibres) of the
human stomach. (A) The stomach of man has a large vertical
and a smaller horizontal or ascending component. The vertical
stomach is conventionally subdivided into fundus and corpus.
The fundus forms a hemisphere upstream from the cardia.
The gastric body (or corpus) is a cylindric segment that extends to the gastric incisura. The horizontal stomach comprises the antrum (inclusive the pylorus) and the sinus. The
antrum is a cone-shaped segment that extends from the incisura to the base of the bulb. The sinus is a wedge-shaped
segment that forms opposite the incisura as the dependent
part of the greater curvature descends towards the pelvis. The
subdivision given here by us follows closely Forsell as quoted
by Torgersen.6 (B) The muscle coat of the saccular stomach
differs from that of the tubular gut. A third or innermost
gastric muscle layer originates from the lower esophageal
sphincter. Its upper slings radiate horizontally towards the
greater curvature, and maintain the angle between the
esophagus and stomach. The lower slings form strong bundles
anterior and posterior to the lesser curvature. From there fibres take off in an arc to fuse with the circular muscle between the curvatures. The lower slings maintain the
angulation between proximal and distal stomach, and suspend
the dependent part of the stomach on the cardia (modified
from Torgensen6). The gastroduodenal junction is suspended
by the hepatoduodenal ligament; this is continuous with the
gastric ligament, a connective tissue septum in the antral
muscle coat.
compliant at and above its inlet, and becomes stiff and
narrow towards its outlet (the diameter of the human
pylorus is 1 cm and less). The proximal fundus/corpus
segment is a spacious reservoir;8,24 the distal antrum/
pylorus segment is a thick walled muscular conduit,
pump and sphincter.8,10–14,17 The fundus, upstream and
lateral from the inlet, resembles a hemisphere when
distended by an air bubble of 2–4 cm height.1,24 The
gastric corpus (body) extends from below the gastric
inlet (cardia) to the incisura angularis. Its lumen is
collapsed in the empty stomach.24 Food boluses entering
the stomach collect below the fundic air bubble, wedge
into the corpus, and slide into the distal stomach (Fig. 2)
along the lesser curvature (Magenstrasse). Additional
contents expand the gastric corpus to a cylindrical
The configuration of the stomach and duodenum,
intragastric layering and flow
At any one time, the shape of the stomach and duodenum is influenced by its contents and by surrounding
organs. Particularly, the liver flattens the stomach. The
proximal stomach assumes an almost vertical position
in upright man, and its distal part ascends to the outlet.8
The inner (medial) curve of the J is known as the lesser
gastric curvature for it is shorter than its opposite at the
outside (lateral) the greater curvature. The lesser curvature is bent at the incisura angularis, the fulcrum
between proximal and distal stomach (Fig. 1). The
stomach is widest (roughly 10 cm in man) and most
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
173
K. Schulze
Neurogastroenterology and Motility
Figure 3 Layering in the human stomach. Food enters the
stomach through the cardia and slides down the lesser curvature, with sequential boluses stacking up like funnels.
Earlier boluses are pushed towards the greater curvature
where they may spread orad. Layering depends on the gastric
volume and on the degree to which the greater curvature
moves away from the lesser curvature. Reconstruction by
Groedel based on serial radiographic observations.
Figure 2 Unfolding and pelvic descent of the human stomach.
The ÔMagenstrasseÕ. (A–D) The fasting stomach is collapsed
except for the fundus which is distended by an air bubble of
200–300 mL. Food passing the cardia collects under the bubble
(A), gradually wedges into the corpus (B), and slides into the
sinus. The high baseline tone of the corpus narrows the passage from the proximal to the distal stomach (C). Sequential
food boluses distend the passage from below (as they accumulate as bolus II in the sinus and as bolus I below the air
bubble (D). The narrow passage shown in (c) is what radiologists refer to as ÔMagenstrasseÕ, a term introduced by anatomists to define the smooth groove the gastric mucosa forms
along the lesser curvature in contrast to the prominent mucosal folds (called gastric rugae) the inner gastric surface forms
in the remainder of the proximal stomach. (E) Pelvic descent
of dependent part (caudal pole) of stomach in response to
eating. The lines represent the outline of the dependent part of
the stomach after 4, 12, 16 and 20 bites. The stomach has
expanded several centimetres towards the pelvis. As the
greater curvature moves caudad and to the left from the
pyloric orifice, the sinus forms between antrum and corpus.
Redrawn from Groedel.
increase with gastric filling (Fig. 2) and decrease as
digestion and emptying proceed.
These anatomical features have likely implications2,8,63–68 for the distribution of luminal contents
and their motions in response to contractions (Fig. 4).
The stomach resembles a bakers decorating bag whose
contents are pressed into an ever narrower and stiffer
conduit. Food layers in the stomach (Fig. 3), and layer
by layer, the gastric contents become pasty then liquid
as they approach the pylorus.24 Sediment and debris
heavier than water collect in the sinus,66,68 whereas fat
floats on top of the gastric contents,2,69,69A and is held
back by the incisura (Fig. 4A). Liquids are made
increasingly viscous as they move distally because
secretions are combined with the tiny particles resulting from the break down of solids.67 At the same time,
the vertical position of the stomach promotes layering
of contents according to density. Recent boluses are
stacked vertically along the lesser curvature, whereas
earlier ones spread horizontally along the greater
curvature (Fig. 3). The leading edge of a bolus pushes
into earlier boluses and spreads them into thin layers.24
Boluses nesting inside earlier boluses escape the low
pH required for peptic digestion and this allows
salivary digestion to continue in an alkaline milieu.24
The very gradual penetration of the food bolus by
lumen whose mucosal folds are flattened.1,24 The
antrum is shaped like a cone when distended and like
a tube when contracted.1,63 The sinus is the wedge
shaped8,24,63 dependent segment of the stomach which
bulges opposite the incisura (Figs 1–3). The distance
between the uppermost pole of the fundus and the
lowermost pole of the sinus averages 20 cm in men and
22 cm in women. The distance from the pole of the sinus
to the gastric outlet averages 8 cm.24 These distances
174
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Volume 18, Number 3, March 2006
Mechanics of digestion
Figure 4 Hypothetical implications of the configuration of the stomach at rest and during digestive activity on the disposition of its
luminal contents. (A) Layering and phase discrimination. Contents layer in the vertical stomach according to their density.
Particles (gravity of 1.2) settle in the sinus, fat (gravity of 0.9) floats on top, with watery contents in between. Watery contents fill
the distal antrum and escape into the descending duodenum ahead of solid particles and fat. Small particles moving with the
aqueous phase advance over the pyloric ridge into the duodenum (decanting), while fat is retained by the incisura (skimming). (B)
Deflection of particles and fat droplets by the antral boundaries. The conical shape of the antrum with the pylorus at its upper end
would acts like an inverted funnel. During flow pulses, watery contents and tiny particles of water density make up the rapid core
stream. Large particles and fat droplets move along the boundaries and are likely to be retained by the walls of the antrum.
Sequential flow pulses would deposit gastric contents in the distal stomach according to their density gradients. (C) Shuttling of
particles by antral contractions. As contractions indent the sinus and the antrum, they propel portions of sediment from the sinus
towards the pylorus. As contraction depth and velocity increases towards the pylorus, particles roll back in a tumbling motion. (D)
Actions of the incisura. As the peristaltic contraction invades the sinus, it lifts sediment up to the incisura. The incisura would
partition, compress and scrape across the sediment similar to the actions of a pestle inside a mortar.
this contributes to sieving. Accordingly, pulses of flow
carry liquids and tiny isodense particles through the
pylorus into the descending duodenum, but stop before
bulkier particles reach the rim formed by the gastroduodenal junction (Fig. 4B). Sieving would be achieved
through a process akin to decanting63 and the antrum
and pylorus would sort contents by density gradients.
Tiny isodense particles would be carried by the core
stream towards the pylorus. Large and comparatively
heavy particles and buoyant fat globules would move at
the fluid boundaries and be deflected by the walls of
the antrum (Fig. 4A,B).
Contractions (Fig. 5) accelerate towards the pylorus4,31 and might outpace particles (Fig. 4C). As contractions approach the pylorus, flow back into the
stomach increases at the expense of flow forward into
the duodenum.1,10,20,22,25,27,30 Retrograde flow (or
Ôbolus escapeÕ) is favoured by the wide open lumen
upstream and the narrow lumen towards the
pylorus.20,23,26,63,65 The above concepts remain to be
tested by rigorous numerical analysis.
gastric secretions has been visualized by echoplanar
imaging.67
The duodenal bulb is a receptacle for gastric effluent.22,25 Pancreatico-biliary secretions and duodenal
contents are also likely to collect in the bulb: all
duodenal contractions return aliquots towards the
pylorus.28,58,59 Nutrients streaming out of the pylorus
would stir the contents of the bulb by a nozzle effect.
The sharp bend between the first and second duodenal
segment probably further deflects and partitions gastric
effluent.
Phase discrimination by the stomach
The segment that includes the pylorus and the distal
antrum are critical to gastric sieving. Sieving refers to
phase discrimination whereby the stomach empties
aqueous solutions, while retaining particles >1 mm in
size, and those of greater or lesser density than water.
Sieving is often simplistically equated with straining
in which soup is passed through a mesh to remove
bulky material. Straining is likely to operate primarily
towards the end of gastric flow pulses when the pylorus
closes ahead of dense and particulate contents. Since
most gastric outflow occurs while the lumina of
stomach and duodenum form a common-cavity30
additional flow phenomena must contribute to sieving.
The gastric outlet is located well above the most
dependent part of the stomach, and it is proposed that
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Computing flow based on boundary movements
The first computations of flow and mixing in the human
stomach was published in December 2004 by the group
of James Brasseur.61 Based on realistic data of the geometry, luminal pressures and boundary movements
from simultaneous MRI and high resolution manometry
175
K. Schulze
Neurogastroenterology and Motility
redraw the borders between the proximal and distal
stomach. Peristaltic contractions are born of tone
contractions as shallow indentations on the proximal
greater curvature, about 15 cm above the pylorus in the
human stomach.1–5,61 Indentations deepen as they
propagate distally and often virtually occlude the antral
lumen (Fig. 4). The frequency and propagation of phasic
contractions are controlled by the gastric pacesetter, an
oscillating membrane potential whose frequency
approximates 3 cycles min)1 in man. Propagation velocity averages 2.5 mm s)1, and increases from the proximal to the distal stomach.1–5,31 At any one time, two to
three peristaltic contractions involve sequential sections of the stomach, each taking approximately 60 s to
advance from the fundus to the pylorus. Peristaltic
contractions indent the gastric wall over the short band
width of 1–2 cm.26,61,65 The contraction width increases
as the contraction approaches the proximal pyloric loop
(Fig. 4) and closes in rapid sequence, a 3 cm or longer
segment of the lumen.22,63 This so-called Ôterminal
antral contractionÕ or Ôantral systoleÕ produces dramatic
flow (see below). Flow in the proximal stomach is slow
by comparison, and occurs over shorter distances.61
Meals, by their volume, chemical and physical
properties, affect the amplitude of contractions, the
length of their propagation (between the sites at which
they originate and where they terminate), and the
duration of time the stomach generates peristalsis.1–5
Large meals stimulate powerful phasic contractions
through the corporo-antral reflex1,33,37,48 and contractions originate higher up in the stomach. Contractions
are deep with aqueous contents, and shallow when
contents are highly viscous.20,23 With liquid meals
containing few calories, the stomach may be empty
after a few contractions. With substantial meals of
meat and vegetables, contractions may go on for hours.
Contractions indent the greater curvature more than
the lesser curvature.1–5,20,23,65 This is because13,14
contractions originate on the proximal greater curvature, and move the compliant greater curvature
towards the stiff lesser curvature (rather than moving
both equally towards a midline). Contractions presumably move more slowly along the shorter lesser than
along the greater curvature, and lead to complex
movements of the incisura while sequentially indenting and lifting the greater curvature from the gastric
body to the antrum.24,79
Figure 5 Changes in configuration of human stomach. As the
contraction advances from 1 to 6, it indents the caudal pole of
the stomach (the sinus) and lifts its up and towards the pylorus.
At the same time, the incisura deepens and forms a more acute
angle between proximal and distal stomach. Note how the
terminal antrum has narrowed at stage 6 as compared with stage
1. Contractions in response to a mixed solid–liquid meal
to which a small amount of barium was added. After Groedel.
in the human stomach, the model demonstrated the
strongest fluid motions around the lumen occlusion
generated by contractions in the antrum. Fluid motions
were of two distinct patterns. The first pattern corresponded to the well known retropulsive jet1,5,20,22,25,30,63
during the terminal antral contraction. Jet velocity
increased up to 7.5 mm s)1 in proportion to lumen
occlusion, but was not affected by pyloric closure or
other physiologic parameters tested. The fluid jet spread
particles along the long axis of the stomach, more so
distally than proximally. The second fluid motion
identified were flow vortices (or eddies) that circulated
particles between successive contraction waves. Flow
eddies have escaped detection by imaging, but are
critical to digestion by producing radial mixing.21,61,62
Eddies might carry gastric secretions from the mucosal
surface towards the core of the gastric lumen, help to
hydrate food boluses, and to carry off surface particles
(elution).
Gastric contractions and dynamic changes in
gastric configuration
Flow in and out of the stomach is mediated by the
complex movements of the gastric boundaries during
contractions. Contractions start as increases in gastric
tone that flatten and narrow the fundus,1,65 shorten the
greater curvature, affect the position of the incisura, and
The terminal antral contraction and the
retrograde jet
Ehrlein and Schemann distinguished three phases of
antral flow in the dog:25 in the first phase of propulsion,
176
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Volume 18, Number 3, March 2006
Mechanics of digestion
and poorly digestible meals lead to profound and
prolonged relaxation of the proximal stomach and
tonic closure of antrum, pylorus and duodenum.22,25,29
Contents may take hours to advance from the proximal
to the distal stomach.1–3,25 Gastric outflow is pulsatile,
with individual flow pulses out of the pylorus in the
range of 2–3 mL after regular meals in dogs.81
Gastric emptying occurs largely as an isotonic
process, through a patent pylorus and without a sizeable antro-duodenal pressure gradient.22,25,30,57,58,65,73
Pressure pulses generated by peristaltic contractions
may modulate outflow, and generate forces that
promote mixing and digestion.65 A recent numerical
analysis sheds additional light on these issues: the
pressure differences necessary to produce pyloric flow
are too small to be measurable by manometry. It was
proposed that Ôthe slight pressurization of the terminal
antrum by an antral contraction wave still several
centimetres from an open pylorus may be sufficient to
significantly augment transpyloric flow generated by
global common cavity pressure difference between the
stomach and duodenum maintained by fundic muscle
toneÕ.61
Liquids clear the stomach at a rate proportional to
their intragastric volume or by first-order-kinetics. The
rate at which the stomach empties increases before it
declines,2,23,25 an emptying pattern best represented by
a power exponential curve.2,5 The forces behind this
are presumably the high gastric wall tension generated
by large volumes and the large volumes displaced by
any contraction in that setting.
Solid particles empty from the stomach by fundamentally different zero-order kinetics, that is independent of gastric volume.2 The stomach retains for
digestion particles whose diameter exceeds 1 mm and
those whose density differs from water. If particles are
ingested at 10 mm size, they are reduced to a median of
0.05 mm upon arrival in the duodenum.2,55 The duration of the digestive phase depends on the physical
properties of the food: soft noodles and eggs are
processed faster than comparatively compact cooked
liver.2,55 If liver is fed as both large and small particles,
both leave the stomach eventually at the same size and
rate, but there is a longer time delay before the large
ones appear. There is, therefore, a delay up to several
hours between the ingestion and the efflux of solids (or
of the chyme that derives from their dispersion). As the
viscosity of gastric contents increases, even large and
dense particles may be dragged along.2,3 The time delay
also reflects the rate at which the proximal stomach
delivers nutrients to the antrum. For this, the stomach
needs to recover its tone and phasic contractions after
the meal and to secrete acid and enzymes that soften
the contraction reaches the proximal antrum, and
drives chyme into the middle and terminal antrum.
In the second phase, evacuation and retropulsion, some
chyme escapes through the relaxed pylorus and some is
returned towards the gastric body. In the third phase,
retropulsion and grinding, the contraction advances at
increasing speed and virtually occludes the terminal
antrum and pylorus lead to forceful grinding and
retropulsion.
Dynamic contrast studies,20,22,25 ultrasound observations,68 and fluid mechanical models61 show the
striking impact of terminal antral contractions on
particle dispersion. C Code commented:1 ÔTerminal
antral contractions mix, reduce the particle size of and
emulsify the gastric contents. Simple mixing of contents accompanies all peristaltic activity. The mixing
activity of the terminal antral contraction is unique.
When the pyloric canal closes…contents are forcefully
retropelled towards the corpus through the narrow
orifice of the advancing contraction. This squirting has
a nozzle effect which mixes and emulsifies contents.
Besides mixing and emulsifying, terminal contractions
rub and grind the contents. No measurements have
been made of the effectiveness of this processÕ.
In preliminary studies, retrograde jets occurred
5.6 + 2.2 s before pyloric closure and lasted 7.2 + 3.1 s.
The leading edge of the jet moved some 15 mm
upstream. The trajectory of individual particles was
much longer, their velocity declined from around
13 mm s)1 at the peak to around 8 mm s)1 towards
the end. As the jet pointed sequentially towards the
gastric cardia and the dependent part of the curvature, it
stirred up sediment and swirled particles in the gastric
body.65,80
The terminal antral contraction produces impressive
flow patterns.1,20,25,34,65 However, jets are no more
than the dramatic finale to digestive processes already
well under way. Normally, only liquid chyme and
small particles79 reach the distal antrum, and even
after the antrum and pylorus are resected, two-thirds of
food particles are adequately digested.2
Forces controlling gastric emptying
Changes in gastric tone (size), and the propagating
indentation of gastric peristalsis provide the momentum to gastric emptying. The emptying rate is determined by the balance between driving and resistive
forces.25 With aqueous and isotonic meals, the proximal stomach shrinks promptly, and the distal stomach and gastroduodenal junction widen. Rapid gastric
outflow is accompanied by net gastric emptying
(reduction in gastric volume). In contrast, high caloric
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
177
K. Schulze
Neurogastroenterology and Motility
and forcefully mixed into nutrients just about to leave
the stomach.
and suspend solids. Solid meals induce more profound
inhibition of gastric contractions than liquids, and also
induce larger secretory responses.67,68 The gastric
emptying of solids is delayed when acid secretion is
suppressed, particularly by proton pump inhibitors.82
The digestion and emptying of solids proceed in
parallel. Not all gastric contents are digested by the
time solids or their derivates start emptying from the
stomach. Hundreds of contraction waves may be
required to digest and empty a solid meal of meat and
vegetables.2,78 The flow generated by each contraction
has to be controlled so that large and compact particles
are retained for digestion while fluid and isodense tiny
particles suspended in the fluid are allowed into the
duodenum. More energy is required to digest meals of
fat and protein than of carbohydrates.2,6,7,52–54 The
steady rate at which the stomach clears solid derivates
has been linked to the intrinsic frequency of the gastric
pacesetter controlling antral contractions. Meyer proposed that the zero-order kinetics for solid emptying
relates to this finite process.2
Duodenal contractions and flow
Duodenal contractions ensure that pancreaticobiliary
secretions work on gastric chyme. Most contractions
occlude the lumen maximally around the middle
section of the descending duodenum, at or below the
papilla of Vater.28,29 From there, the contraction
expands proximally and distally, separating contents
and moving some towards the stomach and some
towards the distal duodenum. As the duodenum
relaxes, these contents would flow back. This to-andfro movement produced by segmental contractions is
likely to have a powerful mixing effect.
The activity of the duodenum28 is highly susceptible
to the chemical composition of luminal contents. In
response to isotonic saline, the human duodenum
generates propagating contractions that swiftly sweep
the bolus caudad. Hypertonic saline or acid elicit a
tonic contraction which virtually occludes the duodenal lumen. Frequent rhythmic contractions lead to
high luminal pressures. Fat makes the duodenum a
flaccid bag whose shallow contractions act on contents
seemingly at random.29
In their classical computations, Macagno and Christensen relied on geometric simplifications to describe
wall movements gleaned from still photos and defined
flow patterns without the benefit of current computing
power. Nevertheless, many of their conclusions
remain valid to date. Thus, they showed that a series
of longitudinal contractions draws a compact fluid
bolus out into thin convoluted layers, which would
promote diffusion and convective mixing.21 They also
demonstrated that retrograde and radial flow60 are
intrinsic features of peristaltic movements in addition
to the laminar antegrade flow they are often naively
identified with.65,87–90
Drug dispersion
Where and how quickly medicinal preparations release
the active drug affects pharmacodynamics, and imaging and modelling is about to revolutionize the design
of drug preparations. Preparations of various size,
composition and fracture strength have been tracked
by echoplanar imaging.66,83–85 The residence time of
particles in the stomach increases with their fracture
strength, just as soft pasta empties faster than more
solid liver.2,54,66
Bidirectional flow across the pylorus and the
nozzle effect. Role of the duodenal bulb (cap)
Flow out of the stomach occurs largely as individual
gushes (pulsatile flow). In dogs, chyme squirts out of the
pylorus about every 12 s, at flow rates at 3 mL s)1 and
higher. Flow turns more steady beyond the duodenal
bulb as more frequent flow pulses move smaller
volumes.81 Pyloric flow resistance of 2.2 mL mmHg s)1
is much higher than duodenal flow resistance
(0.7 mL mmHg s)1), which still dampens gastric outflow.29 Chyme squirts out of the narrow pyloric orifice
into the wide duodenal bulb to form a vortex. This
nozzle effect is likely to mix gastric effluent with
duodenal contents and pancreaticobiliary secretions.
In up to 60% of gastric contraction cycles, the
duodenal bulb contracts before the terminal antrum.
This leads to retrograde flow across the pylorus.25,86
Pancreaticobiliary secretions might thus be injected
Gastrointestinal secretions, and the hydration,
dilution and elution of food
To the food and drink ingested, the stomach and
duodenum add their secretions. Malagelada has estimated that the cumulative volume cleared by the
stomach is double or triple the volume of the original
meal.3,53 Ehrlein found that the stomach of dogs fed
mashed potatoes and olive oil enlarged over the first
hour before outflow outweighed secretory input.23,25
Secretions render meals less compact and less concentrated. Nutrients are hydrated and diluted to
decrease their physical consistency, caloric density
178
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Volume 18, Number 3, March 2006
Mechanics of digestion
and osmolality.2,4 Swelling, softening, and disintegration of particles serve to suspend them and carry them
in liquid medium. In currents and counter currents
particles are further ground down by shear stresses and
are effectively mixed with digestive secretions.
Contemporary imaging can directly visualize how
the physical state of food is altered by digestion.1,2,78
When the gastric dilution of a highly viscous polysaccharide meal was monitored by echoplanar imaging,67
secretions diluted initially only the contents close to
the gastric walls. In the second hour, secretions
penetrated the core of the food bolus. Contractions
moved solid gastric contents in a process of elution as
they rushed fluid over the surface of the softened food
bolus. This is similar to how discrete beans were
transformed over hours of contractions into a paste,
bits of which were dragged out of the pylorus by fluid
streams.63,65
The suppression of gastric acid secretion slows
gastric emptying, even of liquids.82 This is related to
the increased intragastric pH and the release of gastrin
which relaxes the proximal stomach and thereby
delays the delivery of gastric contents. How the lack
of secretions interferes with digestive processes has not
been studied in detail.
In the duodenum, the gastric effluent is exposed to
bile and to pancreatic secretions. Gallbladder contractions and pancreaticobiliary flow alternate with the
gastric emptying of fats, presumably to allow for
effective mixing of fats, bile salts and enzymes.91–95
Bicarbonate neutralizes gastric acid, and allows pancreatic enzymes to reduce proteins to amino acids, and
carbohydrates to hexoses. Bile salts clear fats by
micellar solubilization; this allows water soluble pancreatic lipases to split fats. Knowledge of these processes derives primarily from in vitro experiments or from
examination by freeze fracture of luminal samples.78,86,95,96 The in vivo topography of these physico-chemical changes remains to be clarified.
under the influence of contractions and secretions of
acid, bicarbonate, bile and enzymes.
Late in digestion, the stomach empties an increasingly pasty chyme. This has been ascribed to lesser
amounts of fluid and secretions available to carry
particles.2,3 However, digestion renders gastric contents increasingly viscous by releasing small particles
into the fluid medium. Viscous solutions would be
expected to carry larger particles in the fluid stream
than aqueous secretions.2,54 Moreover, as the stomach
shrinks in size, its greater curvature shortens and
moves towards the lesser curvature. This lifts sediment and debris from its dependent parts towards the
pylorus.2,54
The size of food particles and fat droplets
Liver ingested as 10 mm cubes is recovered in duodenal samples as particles well below 1 mm: 95% of
particles are <0.5 mm in size, and their median
distribution corresponds to a tiny 50 lm.2,7,54 Breaking
up a few large particles into many tiny particles
enlarges the surface at which enzymes attack substrate. Dogs normally absorb up to 85% of fat from
liver. Once the dogs undergo a truncal vagotomy with
antrectomy, they absorb less than half the liver fat.
Less complete break down in the stomach means half
the liver particles are still 0.5 mm or larger in the midintestine, and do not release intracellular fat for
digestion and absorption.2,54
Fat may be liquid or solid at ingestion2,54 and is less
dense (specific gravity of 0.9) than water and most solid
foods (specific gravity of 1.2). Fat is easily dispersed
into tiny spherules, but these may coalesce into larger
globules unless they are stabilized or attach to the
hydrophobic surfaces of food particles.6,52,86,95,96
Armand and coworkers have studied the emulsification of fat by the stomach and duodenum.97–103 The
stomach reduced the median diameter of fat droplets
from around 57 to 17 lg. This increased the emulsion
surface area from 0.7 m2 g)1 lipid to 2.1 m2 g)1 in the
stomach and to 1.6 m2 g)1 in the duodenum. At 1 h,
the mean concentration of emulsion surface was
270 m2 L)1 in the stomach and 78 m2 L)1 in the
duodenum.
Chyme and its constituents
Chyme is food altered by the mechanical and secretory
activity of the stomach and intestines. It is a multiphase slurry of nutrients in various physical states
(liquid, globular, pasty or particulate) suspended in
secretions. The suspension serves luminal transit,
enzymatic digestion and absorption. Chyme composition has not been mapped in detail over the course of
digestion or at precise points in the stomach and
duodenum. It is likely that within any bolus of chyme
zones of specific pH, of stages of micellar solubilization
and of nutrient hydrolysis rapidly form and disappear
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
FUTURE CHALLENGES
Modern imaging has greatly advanced the understanding of gastroduodenal flow processes. It should lead to
more precise definition of particle trajectories, flow
velocities, particle dispersion, fat emulsification and
the formation of chyme. Contemporary computations
179
K. Schulze
Neurogastroenterology and Motility
have informed on the flow of aqueous solutions and
on the flow of particles that are isodense and move
with the solution. Future computations should
investigate more viscous solutions and particles that
interact with the solution or each other. The importance of direct compression vs shear stresses in particle
dispersion, and other digestive processes remains to
be quantified. Imaging and computations will furthermore have to face the additional complexities posed
by recording and comprehending gastroduodenal flow
in 3D and 4D.
15
16
17
18
19
REFERENCES
1 Code CF, Carlson HC, Motor activity of the stomach. In:
Code CF, ed. Handbook of Physiology Alimentary
Canal IV. Washington, DC: American Physiological
Society, 1968: 1903–16.
2 Meyer JH. The physiology of gastric motility and gastric
emptying. In: Yamada T, ed. Textbook of Gastroenterology. JB Lippincott, Philadelphia, 1991: 137–57.
3 Malagelada JR, Azpiros F., Determinants of gastric emptying and transit in the small intestine. In: Schultz SG,
Wood JD, eds. Handbook of Physiology Gastrointestinal System VI. Bethesda, MD: American Physiological
Society, 1989: 909–38.
4 Mayer EA. The physiology of gastric storage and emptying. In: Johnson L, ed. Physiology of the Gastrointestinal
Tract, 3rd edn. New York: Raven Press, 1994: 929–76.
5 Camilleri M, Prather CM. Gastric motor physiology
and motor disorders. In: Feldmann M, Scharschmidt BF,
Sleisenger MH, eds. Sleisenger and Fordtran’s Gastrointestinal and Liver disease, 6th edn. WB Saunders Co,
Philadelphia, 1993: 572–86.
6 Meyer JH, Mayer EA, Gu JY, Fink AS, Fried M. Gastric
processing and emptying of fat. Gastroenterology 1986;
90: 1176–87.
7 Meyer JH, Thomson JB, Cohen MB et al. Sieving of solid
food by the canine stomach and sieving after gastric
surgery. Gastroenterology 1979; 76: 804.
8 Torgersen J. The muscular build and movements of the
stomach and duodenal bulb. Acta Radiol 1942; 45: 1–
187.
9 Gregersen H, Kassab G. Biomechanics of gastrointestinal
tract. Neurogastroenterol Motil 1996; 8: 277–97.
10 Staadas J, Aune S. Intragastric pressure/volume relationship before and after vagotomy. Acta Chir Scand 1970;
136: 611–15.
11 Biancani P, Zabinski MP, Kerstein MD, Behar J.
Mechanical characteristics of the cat pylorus. Gastroenterology 1979; 77: 301–9.
12 Gao C, Arendt-Nielsen L, Liu W, Petersen P, Drewes AM,
Gregersen H. Sensory and biomechanical responses to
ramp-controlled distension of the human duodenum. Am
J Physiol Gastrointest Liver Physiol 2003; 284: G461–71.
13 Kita Y. Elastic-Model driven analysis of several views of a
deformable cylindrical object. IEEE Trans PAMI 1996; 18:
1150–62.
14 Gregersen H, Gilja OH, Hausken T et al. Mechanical
properties in the human gastric antrum using B-mode
20
21
22
23
24
25
26
27
28
29
30
31
32
33
180
ultrasonography and antral distension. Am J Physiol
Gastrointest Liver Physiol 2002; 283: G368–75.
Gao C, Zhao J, Gregersen H. Histomorphometry and
strain distribution in pig duodenum with reference to
zero-stress state. Dig Dis Sci 2000; 45: 1500–8.
Gregersen H, Kassab G, Pallencaoe E et al. Morphometry
and strain distribution in guinea pig duodenum with
reference to the zero-stress state. Am J Physiol 1997; 273:
G865–74.
Schulze-Delrieu K, Shirazi SS. Neuromuscular differentiation of the human pylorus. Gastroenterology 1983; 84:
287–92.
Camilleri M. The duodenum: a conduit or a pump? Gut
1997; 41: 714.
De Schepper HU, Cremonini F, Chitkara D, Camilleri M.
Assessment of gastric accommodation: overview and
evaluation of current methods. Neurogastroenterol Motil
2004; 16: 275–85.
Carlson HC, Code CF, Nelson RA. Motor action of the
canine gasrtoduodenal junction; a cineradigraphic, pressure and electric study. Am J Dig Dis 1966; 11: 155–72.
Melville J, Macagno E, Christensen J. Longitudinal contractions in the duodenum: their fluid-mechanical function. Am J Physiol 1975; 228: 1887–92.
Keet AD. The prepyloric contractions in the normal
stomach. Acta Radiol 1958; 48: 413–24.
Keinke O, Ehrlein HJ. Effect of oleic acid on canine gastroduodenal motility, pyloric diameter and gastric emptying. Q J Exp Physiol 1983; 68: 675–86.
Groedel FM. Die Roentgenuntersuchung des Magens. In:
Groedel FM, ed. Roentgendiagnostik in der Inneren
Medizin. Lehmann’s Verlag, Muenchen, 1924: 502–5.
Keinke O, Schemann M, Ehrlein HJ. Mechanical factors
regulating gastric emptying of viscous nutrient meals in
dogs. Q J Exp Physiol 1984; 69: 781–95.
Faas H, Hebbard GS, Feinle C et al. Pressure-geometry
relationship in the antroduodenal region in humans. Am J
Physiol Gastrointest Liver Physiol 2001; 281: G1214–20.
Wright J, Evans D, Gowland P, Mansfield P. Validation of
antroduodenal motility measurements made by echoplanar magnetic resonance imaging. Neurogastroenterol
Motil 1999; 11: 19–25.
Castedal M, Bjornsson E, Abrahamsson H. Postprandial
peristalsis in the human duodenum. Neurogastroenterol
Motil 1998; 10: 227–33.
Rao SSC, Lu C, Schulze-Delrieu K. Duodenum as an
immediate brake to gastric outflow: a videofluoroscopic
and manometric assessment. Gastroenterology 1996;
110: 740–7.
Pallotta N, Cicala M, Frandina C, Corazziari E. Antropyloric contractile patterns and transpyloric flow after
meal ingestion in humans. Am J Gastroenterol 1998; 93:
2513–22.
Bauer AJ, Publicover NG, Sanders KM. Origin and spread
of slow waves in canine gastric antral circular muscle.
Am J Physiol 1985; 249: G800.
Berthoud HR, Blackshaw LA, Brookes SJ, Grundy D.
Neuroanatomy of extrinsic afferents supplying the gastrointestinal tract. Neurogastroenterol Motil 2004; 16:
28–33.
Feinle C, Grundy D, Read NW. Effects of duodenal
nutrients on sensory and motor responses of the
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Volume 18, Number 3, March 2006
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
Mechanics of digestion
52 Cortot A, Phillips SF, Malagelada JR. Gastric emptying of
lipids after ingestion of a solid-liquid meal in humans.
Gastroenterology 1981; 80: 922–7.
53 Dubois A, Natelon BH, van Eerdewegh P, Gardner JD.
Gastric emptying and secretion in the rhesus monkey.
Am J Physiol 1977; 323: E186–92.
54 Ohashi H, Meyer JH. Effect of peptic digestion on emptying of cooked liver in dogs. Gastroenterology 1980; 79:
305–10.
55 Sandhu KS, el Samahi MM, Mena I, Dooley CP, Valenzuela JE. Effect of pectin on gastric emptying and gastroduedenal
motility
in
normal
subjects.
Gastroenterology 1987; 92: 486–92.
56 Prather CM, Camilleri M, Thomforde GM, Forstrom LA,
Zinsmeister AR. Gastric axial forces in experimentally
delayed and accelerated gastric emptying. Am J Physiol
1993; 264: 0G928–34.
57 Hausken T, Mundt M, Samson M. Low antroduodenal
pressure gradients are responsible for gastric emptying of
a low-caloric liquid meal in humans. Neurogastroenterol
Motil 2002; 14: 97–105.
58 Anvari M, Dent J, Malbert C, Jamieson GG. Mechanics of
pulsatile transpyloric flow in the pig. J Physiol 1995; 488:
193–202.
59 Rao SSC, Safedi R, Lu C, Schulze-Delrieu K. Manometric
responses of human duodenum during infusion of HCl,
hyperosmolar saline, bile and oleic acid. Neurogastroenterol Motil 1996; 8: 35–43.
60 Macagno EO, Christensen J. Fluid mechanics of gastrointestinal flow. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract. New York: Raven Press, 1981:
335–58.
61 Pal A, Indireshkumar K, Schwizer W, Abrahamsson B,
Fried M, Brasseur JG. Gastric flow and mixing studied
using computer stimulation. Proc R Soc Lond B Biol Sci
2004; 271: 2587–94.
62 Jeffrey B, Udaykumar HA, Schulze K. Flow Fields generated by peristaltic reflex in isolated guinea pig ileum:
impact of depth and of shoulders of contraction. Am J
Physiol Gastrointestin Liver Physiol 2003; 285: G907–
G918.
63 Brown BP, Schulze-Delrieu K, Schrier JE, Abu-Yousef
MM. The configuration of the human gastroduodenal
junction in the separate emptying of liquids and solids.
Gastroenterology 1993; 2: 433–40.
64 Marciani L, Young P, Wright J et al. Antral motility
measurements by magnetic resonance imaging. Neurogastroenterol Motil 2001; 13: 511–8.
65 Schulze-Delrieu K, Herman RJ, Shirazi SS, Brown BP.
Contractions move contents by changing the configuration of the isolated cat stomach. Am J Physiol 1998; 274:
G359–69.
66 Marciani L, Little SL, Snee J et al. Echo-planar magnetic
resonance imaging of Gaviscon alginate rafts in-vivo. J
Pharm Pharmacol 2002; 54: 1351–6.
67 Marciani L, Gowland PA, Fillery-Travis A et al. Assessment of antral grinding of a model solid meal with echoplanar imaging. Am J Physiol Gastrointest Liver Physiol
2001; 280: G844–9.
68 Marciani L, Gowland PA, Spiller RC et al. Effect of meal
viscosity and nutrients on satiety, intragastric dilution
and emptying assessed by MRI. Am J Physiol Gastrointest Liver Physiol 2001; 280: G1227–33.
human stomach to distension. Am J Physiol 1997; 273:
G721–6.
Grundy D, Bagaev V, Hillsley K. Inhibition of gastric
mechanoreceptor discharge by cholecystokinin in the rat.
Am J Physiol 1995; 268: G355–60.
Schemann M, Grundy D. Electrophysiological identification of vagally innervated enteric neurons in guinea pig
stomach. Am J Physiol 1992; 263: G709–18.
Hillsley K, Schemann M, Grundy D. Alpha-adrenoreceptor modulation of neurally evoked circular muscle responses of the guinea pig stomach. J Auton Nerv Syst
1992; 40: 57–62.
Blackshaw LA, Grundy D. Locally and reflexly mediated
effects of cholecystokinin-octapeptide on the ferret
stomach. J Auton Nerv Syst 1991; 36: 129–37.
Yuan SY, Costa M, Brookes SJ. Neuronal control of the
pyloric sphincter of the guinea pig. Neurogastroenterol
Motil 2001; 13: 187–98.
Hennig GW, Brookes SJ, Costa M. Excitatory and inhibitory motor reflexes in the isolated guinea-pig stomach.
J Physiol 1997; 501: 197–212.
Schemann M, Neunlist M. The human enteric nervous
system. Neurogastroenterol Motil 2004; 16: 55–9.
Tack JF, Wood JD. Synaptic behaviour in the myenteric
plexus of the guinea-pig gastric antrum. J Physiol 1992;
445: 389–406.
Tack JF, Wood JD. Electrical behaviour of myenteric
neurons in the gastric antrum of the guinea pig. J Physiol
1992; 447: 49–66.
Schicho R, Schemann M, Holzer P, Lippe IT. Mucosal
acid challenge activates nitrergic neurons in myentric
plexus of rat stomach. Am J Physiol Gastrointest Liver
Physiol 2001; 281: 0G1316–21.
Schemann M, Reiche D, Michel K. Enteric pathways in
the stomach. Anat Rec 2001; 262: 47–57.
Reiche D, Michel K, Pfannkuche H, Schemann M. Projections and neurochemistry of interneurones in the
myentric plexus of the guinea-pig gastric corpus. Neurosci Lett 2000; 295: 109–12.
Michel K, Reiche D, Schemann M. Projections and
neurochemical coding of motor neurons to the circular
and longitudinal muscle of the guinea pig gastric corpus.
Pflugers Arch 2000; 440: 393–408.
Vanden Berghe P, Coulie B, Tack J, Mawe GM, Schemann
M, Janssens J. Neurochemical coding of myenteric neurons
in the guinea pig antrum. Cell Tissue Res 1999; 297: 81–90.
Edin R, Lundberg J et al. Evidence for vagal enkephalinergic neutral control of the feline pylorus and stomach.
Gastroenterology 1980; 78: 492–7.
Liau SS, Camilleri M, Kim DY, Stephens D, Burton DD,
O’Conner MK. Pharmacological modulation of human
gastric volumes demonstrated non-invasively using
SPECT imaging. Neurogastroenterol Motil 2001; 13: 533–
42.
Delgado-Aros S, Kim DY, Burton DD et al. Effect of GLP1 gastric volume, emptying, maximum volume ingested
and postprandial symptoms in humans. Am J Physiol
Gastrointest Liver Physiol 2002; 282: G424–31.
Samsom M, Szarka LA, Camilleri M, Vella A, Zinsmeister AR, Rizza RA. Pramlintide, an amylin analog,
selectively delays gastric emptying: potential role of vagal
inhibition. Am J Physiol Gastrointest Liver Physiol 2000;
278: G946–51.
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
181
K. Schulze
Neurogastroenterology and Motility
69 Boulby P, Moore R, Gowland P, Spiller RC. Fat delays
emptying but increases forward and backward antral flow
as assessed by flow-sensitive magnetic resonance imaging. Neurogastroenterol Motil 1999; 11: 27–36.
69A Brown BP, Gross J, Schulze-Delrieu K, Carmichael DC,
Barloon TJ, Abu-Yousef M. Layering of fat and intermittent cessation of antral contractions delay fat emptying in the human stomach. Gastroenterology 1994;
106: A472.
70 Schwizer W, Fox M, Steingotter A. Non-invasive investigation of gastrointestinal function with magnetic resonance imaging: towards an ÔidealÕ investigation of
gastrointestinal function. Gut 2003; 52: 34–9.
71 Schwizer W, Steingotter A, Fox M et al. Non-invasive
measurement of gastric accommodation in humans. Gut
2002; 51: 59–62.
72 Faas H, Hebbard GS, Feinle C. Pressure-geometry
relationship in the antroduodenal region in humans.
Am J Physiol Gastrointest Liver Physiol 2001; 281: 1214–
20.
73 Indireshkumar K, Brasseur JG, Faas H et al. Relative
contributions of Ôpressure pumpÕ and Ôperistaltic pumpÕ to
gastric emptying. Am J Physiol Gastrointest Liver Physiol 2000; 278: G604–16.
74 Borovicka J, Lehmann R, Kunz P et al. Evaluation of
gastric emptying and motility in diabetic gastroparesis
with magnetic resonance imaging: effects of cisapride.
Am J Gastroenterol 1999; 94: 2866–73.
75 Kunz P, Feinle C, Schwizer W, Fried M, Boesiger P.
Assessment of gastric motor function during the emptying of solid and liquid meals in humans by MRI. J Magn
Reson Imaging 1999; 9: 75–80.
76 Feinle C, Kunz P, Boesiger P, Fried M, Schwizer W.
Scintigraphic validation of a magnetic resonance imaging
method to study gastric emptying of a solid meal in
humans. Gut 1999; 44: 106–11.
77 Kunz P, Crelier GR, Schwizer W et al. Gastric emptying
and motility: assessment with MR imaging-preliminary
observations. Radiology 1998; 207: 33–40.
78 Cannon WB. The Effects of Stomach Movements on the
Contents. In: Cannon WB, ed. Mechanical Factors of
Digestion, Chapter VI. Abindgon: Oxford Historical
Books, 1996: 59–70.
79 Donner MW. Normal and abnormal motility of the
stomach. Radiol Clin North Am 1976; 14: 441–6.
80 Schulze-Delrieu K, Cook J, Herman B, Shirazi S, Brown B.
Contractions in the isolated cat stomach produce retrograde jets which disperse digestible particles. Gastroenterology 1996; 110: A754.
81 Malbert CH, Ruckebusch Y. Duodenal bulb control of the
flow rate of digesta in the fasted and fed dog. J Physiol
1989; 409: 371–84.
82 Parkman HP, Urbain JL, Knight LC, Brown KL, Trate
DM, Miller MA, Maurer AH, Fisher RS. Effect of gastric
acid suppressants on human gastric motility. Gut 1998;
42: 243–50.
83 Steingoetter A, Weishapt D, Kunz P, Mader K, Lengsfeld
H, Thumshirn M, Boesiger P, Fried M, Schwizer W.
Magnetic resonance imaging for the in vivo evaluation of
gastric-retentive tablets. Pharm Res 2003; 20: 2001–7.
84 Steingoetter A, Kunz P, Weishaupt D, Mader K, Lengsfeld
H, Thumshirn M, Boesiger P, Fried M, Schwizer W.
Analysis of the meal-dependent intragastric performance
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
182
of a gastric-retentive tablet assess by magnetic resonance
imaging. Aliment Pharmacol Ther 2003; 18: 713–20.
Faas H, Steingoetter A, Feinle C, Rades T, Lengsfeld H,
Boesiger P, Fried M, Schwizer W. Effects of meal consistency and ingested fluid volume on the intragastric distribution of a drug model in humans – a magnetic
resonance imaging study. Aliment Pharmacol Ther 2002;
16: 217–24.
Meyer JH. Control of canine gastric emptying of fat by
lipolytic products. Am J Physiol 1994; 266: G1017–35.
Hennig GW, Costa M, Chen BN, Brookes SJ. Quantitative
analysis of peristalsis in the guinea-pig small intestine
using spatio-temporal maps. J Physiol 1999; 507: 575–90.
Berthoud HR, Hennig G, Campbell M, Volaufova J, Costa
M. Video-based spatio-temporal maps for analysis of
gastric motility in vitro: effects of vagal stimulation in
guinea-pigs. Neurogastroenterol Motil 2002; 14: 677–88.
Schulze-Delrieu K. Visual parameters define the phase
and the load of contractions in isolated guinea pig ileum.
Am J Physiol 1999; 276: G1417–24.
Schulze-Delrieu K. Intrinsic differences in the filling response of the guinea pig duodenum and ileum. J Lab Clin
Med 1991; 117: 44–50.
Pallotta N, Calabrese E, Alghisi F, Corazziari E. Ultrasonography in the assessment of gastric and gallbladder
motor function. Diabetes Nutr Metab 2004; 17: 37–42.
Pallotta N. Ultrasonography in the assessment of gallbladder motor activity. Dig Liver Dis 2003; 35: S67–9.
Pallotta N, Corazziari E, Scopinaro F, Bonino R, Schillaci
O, Vignoni A, Mangano M, Torsoli A. Noninvasive estimate of bile flux through the gallbladder in humans. Am J
Gastroenterol 1998; 93: 1877–85.
Pallotta N, Corazziari E, Biliotti D, Torsoli A. Gallbladder
volume variations after meal ingestion. Am J Gastroenterol 1994; 89: 2212–6.
Carriere F, Barrowman JA, Verger R, Laugier R. Secretion
and contribution to lipolysis of gastric and pancreatic
lipases during a test meal in humans. Gastroenterology
1993; 105: 876–88.
Rigler MW, Honkanen RE, Patton JS. Visualization by
freeze fracture, in vitro and in vivo, of the products of fat
digestion. Gastroenterology 1986; 90 (5 Pt 1): 1176–87.
Armand M, Borel P, Dubois C, Senft M, Peyrot J, Salducci
J, Lafont H, Lairon D. Characterization of emulsions and
lipolysis of dietary lipids in the human stomach. Am J
Physiol 1994; 266 (3 Pt 1): G372–81.
Pafumi Y, Lairon D, de la Porte PL, Juhel C, Storch J,
Hamosh M, Armand M. Mechanisms of inhibition of
triacylglycerol hydrolysis by human gastric lipase. J Biol
Chem 2002; 277: 28070–9.
Borel P, Pasquier B, Armand M, Tyssandier V, Grolier
P, Alexandre-Gouabau MC, Andre M, Senft M, Peyrot J,
Jaussan V, Lairon D, Azais-Braesco V. Processing of
vitamin A and E in the human gastrointestinal tract.
Am J Physiol Gastrointest Liver Physiol 2001; 280:
G95–G103.
Armand M, Pasquier B, Andre M, Borel P, Senft M, Peyrot
J, Salducci J, Portugal H, Jaussan V, Lairon D. Digestion
and absorption of 2 fat emulsions with different droplet
sizes in the human digestive tract. Am J Clin Nutr 1999;
70: 1096–106.
Armand M, Borel P, Pasquier B, Dubois C, Senft M,
Andre M, Peyrot J, Salducci J, Lairon D. Physicochemical
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
Volume 18, Number 3, March 2006
Mechanics of digestion
characteristics of emulsions during fat digestion in human stomach and duodenum. Am J Physiol 1996; 271 (1
Pt 1): G172–83.
102 Pasquier B, Armand M, Castelain C, Guillon F, Borel P,
Lafont H, Lairon D. Emulsification and lipolysis of triacylglycerols are altered by viscous soluble dietary fibers
2006 The Author
Journal compilation 2006 Blackwell Publishing Ltd
in acidic gastric medium in vitro. Biochem J 1996;
314 (Pt 1): 269–75.
103 Armand M, Hamosh M, DiPalma JS, Gallagher J, Benjamin SB, Philpott JR, Lairon D, Hamosh P. Dietary fat
modulates gastric lipase activity in healthy humans. Am
J Clin Nutr 1995; 62: 74–80.
183