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GASTROINTRESTINAL PHYSIOLOGY I
GENERAL PRINCIPLES OF GASTROINTESTINAL
FUNCTION — MOTILITY, NERVOUS AND HORMONAL CONTROL
MECHANISMS OF MIXING OF FOOD AND PROPULSION
SECRETORY FUNCTION OF SALIVARY GLANDS, STOMACH, PANCREAS
AND GALLBLADDER
Jana Jurčovičová
GENERAL PRINCIPLES OF GASTROINTESTINAL
FUNCTION
The alimentary tract provides the organism with:
water, electrolytes and nutrients.
It requires:
1 - movement of food through the alimentary tract
2 - secretion of digestive juices and digestion of the food
3 - absorption of the digestive products, water, and electrolytes
4 - circulation of blood through the gastrointestinal organs to
distribute the absorbed substances
5 – regulation of these functions by the nervous and hormonal
systems
THE ENTIRE ALIMENTARY
TRACT.
Each part is adapted to the
specific function
Esophagus, a simple passage
of food
Stomach for a storage and
mixing of food, preparing od
chyme
Small intestine for the
digestion and absorption
Large intestine for electrolyte
and water reabsorption, mass
movement,finaml formation of
feces
CHARACTERISTICS OF THE GASTROINTESTINAL
WALL
The smooth muscle fibers of GIT are
arranged in bundles of ~ 1000 parallel
fibers. In the longitudinal muscle layers
they extend down the intestinal tract, in the
circular one around the gut.
The muscle fibers are electrically
connected through gap junctions allowing
low resistance movement of ions from cell
to cell. They are separated from each other
by loose connective tissue, but they fuse at
many points.
Each muscle layer represents
a branching laticework of bundles
functioning as a syncytium,
Cross-section of the gut wall
GASTROINTESTINAL MOTILITY IS SECURED BY:
-electric activity of the gastrointestinal smooth muscle. In the GIT smooth
muscle the channels responsible for action potentials are calcium-sodium
channels. Large number of Ca++ ions and small number of Na+ ions enter
the fibers. These channels are slower to open and to close than the rapid
sodium channels and accounts for longer duration of action potentials.
ELECTRICAL ACTIVITY OF GIT SMOOTH MUSCLE
The smooth muscle cells of the GIT is subjected to continual and slow
electric activity originating in the enteric nervous system.
Two basic types of electric waves: slow waves and spikes
Slow waves: occur rhythmically by slow waves in the smooth muscle membrane
potential. These are not action potentials.
Intensity -5 and 15 mV, frequency – 3 and 12 per minute. The slow waves do not
cause contraction (except in stomach) they control the appearance of spike potentials,
and spikes potentials cause most of the muscle contraction.
Spike potentials: - true action potentials, when membrane potentials of the smooth
muscle cell becomes more positive than -40 mV.
Under normal conditions the membrane potential is ~ 56 mV.
At more positive value - depolarization of the membrane, becomes more excitable.
At more negative value – hyper polarization of the membrane - less excitable
Factors depolarizing the membrane: stretching of the muscle, stimulation by
acetylcholine,stimulation by parasympathetic nerves secreting acetylcholine,
stimulation by specific GIT hormones
Factors hyperpolarizing the membrane: action of norepinephrine, epinephrine on the
membrane,
stimulation of the sympathetic nerves secreting norepinephrine at their endings.
GASTROINTESTINAL MOTILITY IS SECURED BY:
-
-
neural control of motility by its own neural system called enteric
nervous system. Different types of enteric neurons in their nerve
endings release great variety of neurotransmitter substances:
acetylcholine (excitatory activity), norepinephrine (inhibitory
activity), serotonin, dopamine, cholecystokinin, substance P,
vasoactive intestinal peptide, somatostatin, bombesin
(mixture of excitatory and inhibitory actions).
In addition, there is an autonomic control of the GIT by
parasympathetic and sympathetic innervations.
-hormonal control of motility is secured mainly by peptide
hormones:
cholecystokinine which is secreted by mucosa of duodenum and
jejunum in response of fatty acids,
secretin released from mucosa in duodenum in response to acidic
gastric juice,
gastrin, which is released by stomach pyloric glands
gastric inhibitory peptide released from upper small intestine in
response to fatty acids and amino acids.
AUTONOMIC NERVOUS SYSTEM (ANS)
PARASYMPATHETIC NERVOUS SYSTEM (PSNS)
specifically is responsible for stimulation of activities that occur when the body is
at rest including
Salivation, Lacrimation, Urination, Digestion, Defecation
PSNS signals are carried from the central nervous system to their targets by a
system of two neurons. The first neuron is referred to as preganglionic or
presynaptic neuron.
This axon extends to a ganglion where it synapses with the second neuron in
the chain. The second neuron is referred to as postganglionic neuron. The
ganglion is usually very close to or is embedded in their target organ. The
PSNS nerve endings secrete acetylcholine
SYMPATHETIC NERVOUS SYSTEM (SNS)
is mainly responsible for stimulating activities associated with “flight or fight “
responses.
PSNS and SNS function in opposite to each other, however, they are
complementary in nature rather than antagonistic.
Preganglionic neuron is short. The SNS nerve endings secrete noradrenaline
PARASYMPATHETIC INNERVATION OF GIT
The parasympathetic supply to the gut is divided into sacral and cranial
divisions.
The cranial parasympathetics are transmitted in the vagus nerve.
These fibers provide inervation of to the esophagus, stomach,
pancreas.
The postganglionic neurons of the parasympathetic system are located in
the myenteric and submucosal plexuses. Stimulation of the
parasympathetic nerves causes general increase in activity of the entire
enteric nervous system.
SYMPATHETIC INNERVATION
The sympathetic fibers originate in the spinal cord and innervate all
portion of the GIT causing many effects opposite to those of
parasympathetic system
PREVERTEBRAL GANGLIA
Prevertebral ganglia, collections of postganglionic sympathetic neuronal cell bodies
in recognizable aggregations and play a
critical role in the innervations of the
abdominal viscera.
Function
They are composed of postganglionic
sympatethic neurons that supply abdominal
and pelvic viscera.
Prevertebral ganglia contain a majority of
integrating neurons that receive nervous
information arising from pregangionic
neurons in the spinal cord and neurons of
the myenteric plexus in the gastrointestinal
tract. The targets of these integrating
neurons are mainly neurons of the enteric
nervous system.
These include
1. the celiac ganglia
2. superior mesenteric ganglia, and
3. inferior mesenteric ganglia
PREVERTEBRAL
GANGLIA
PARASYMPATHETIC
NERVOUS SYSTEM
Cranial
vagus
SYMPATHETIC
NERVOUS SYSTEM
NEURAL CONTROL OF THE GUT WALL
GASTROINTESTINAL REFLEXES
The functional connections of the enteric nervous system with the sympathetic and
parasympathetic system allow 3 types of gastrointestinal reflexes essential for the
control of GIT:
Reflexes that occur entirely within the enteric nervous system.
These control GITsecretion, peristalsis, mixing contractions, local inhibitory effects.
Reflexes from the gut to prevertebral sympathetic ganglia and back to GIT.
These transmit signals for long distances in the GIT such as signals from the
stomach to cause emptying of the colon ( gastrocolic reflex), signals from the colon
and small intestine to inhibit stomach motility and secretion (enterogastric
reflexes), and reflexes to inhibit emptying of ileal contents into the colon
(colonoileal reflex)
Reflexes from the gut to the spinal cord or brain stem and back to GIT.
They include: reflexes from the stomach and duodenum to the brain stem and back
by way of the vagus nerve to control gastric motor and secretory activity, and
defecation reflex that travels to the spinal cord and back again to produce powerful
colonic, rectal and abdominal contractions
FUNTIONAL TYPES OF MOVEMENTS IN THE GIT
Two types of movement in the GIT:
Propulsive movement which cause food to move forward along the tract at an
appropriate rate for digestion and absorption
Mixing movement that keeps the intestinal content mixed
Propulsive movement – peristalsis a contracting ring appears around the gut and
moves forward. Thus any material in front of a contractile ring moves forward.
Peristalsis is a inherent property of many syncytial smooth muscle tubes;
Stimulation at any point can cause a contractile ring to appear in the circular
muscle of the gut. The stimulus for peristalsis is distension of the gut. The stretching
of the gut wall stimulates predominantly VIP neurons to contract the gut 2 – 3 cm
above this point , and a contractile ring appears and initiates the peristalsis. Effectual
peristalsis requires an active myenteric plexus (atropine paralyzing cholinergic nerve
system can depress peristalsis).
After the initiation of the peristalsis, the intestinal content is pushing in anal direction
for 5-10 cm before dying out. At the same time gut relaxes several cm downstream
towards the anus which is called receptive reflex. It allows the food to be propelled
analward. This does not appear in the absence of myenteric plexus. The complex is
called myenteric reflex or peristaltic reflex. The peristaltic reflex plus the analward
direction of movement of the peristalsis is called
“THE LAW OF THE GUT”
PROPULSIVE MOVEMENT
HORMONAL CONTROL OF GIT MOTILITY
Some hormones of the GIT have beside the (main) secretory function also motility
effects. Following hormones are of importance:
Cholecystokinin-secreted by mucosa cells of the duodenum and jejunum in response
to the fatty acids, and monoglycerides, the breakdown products of fat. It increases
the contractility of gallbladder to expel bile into the small intestine. It also
inhibits stomach motility, to give adequate time for fat digestion.
Secretin-is secreted by “S” cells in the mucosa of the duodenum in response to acidic
gastric juice emptied from the stomach through the pylorus. It has mild inhibitory
effect on the motility of GIT
Gastric inhibitory polypeptide- is secreted by the mucosa of the upper small
intestine, in
response to fatty acids, amino acids and glucose. It decreases motor activity of the
stomach and thus slows the emptying of gastric content when upper small intestine is
oversupplied. It stimulates also insulin secretion from pancreatic B cells (GIP –
Glucose dependent insulinotropic polypeptide)
Gastrin- is released from the gastral mucosa in response to meat digestive product. It
has stimulatory effect on stomach emptying .
GASTROINTESTINAL BLOOD FLOW
Blood from gut, spleen, pancreas
enter the liver via portal vein. In the liver
blood passes through million of liver
sinusoids, and leaves by way of hepatic
vein into vena cava. The blood vessel
system of the GIT is called splanchnic
circulation. It includes blood flow through
the gut, spleen, pancreas and the liver.
The reticuloendothelial cells line the
sinusoids and remove foreign bacteria
entering blood stream from the GIT.
splanchnic circulation
Most of the non-fat water soluble nutrients
are transported to the liver sinusoids. Here
the parenchymal cells absorb from blood
and store up to ¾ of all absorbed nutrients.
The non-water soluble fat-based nutrients
are absorbed into the intestinal lymphatics,
and conducted to blood via thoracic duct.
TRANSPORT AND MIXING OF FOOD
(MOUTH – ESOPHAGUS- STOMACH)
The amount of food ingested is determined by the intrinsic desire for food hunger
Mechanical aspects of food ingestion –
CHEWING AND SWALLOWING
CHEWING is important for digestion because the digestive enzyme in
saliva act only on the surface of food particle. Moreover raw vegetables
has indigestible cellulose membranes that is to be first broken.
SWALLOWING is divided into:
voluntary stage which initiate the swallowing process,
pharyngeal stage which is involuntary and constitute the passage of food
into esophagus,
esophageal stage involuntary stage that promotes passage of food from
pharynx to stomach. These processes are regulated by impulses
transmitted from mouth by sensory nerves to nucleus tractus solitarius in
medulla oblongata.
CHEWING - MASTICATION Chewing process is caused by the chewing reflex.
The bolus of the food initiate the reflex inhibition of the muscles of mastication and
jawdrops. The drop initiates the stretch reflex of the jaw muscle that leads to
rebound contraction. Proper chewing is important for good contact of the food
with digestive enzymes, since they act on the surface of the particles.
SWALLOWING - DEGLUTION
Voluntary stage – the food is posteriorly
squeezed to the pharynx by pressure of the
tongue
Pharyngeal stage – the trachea is closed, the
oesophagus opens, and the peristaltic waves
forces the bolus of food down. The sensitive
tactile area is a ring around pharyngeal
opening. Impulses are transmitted to medulla
oblongata and nucleus tractus solitarius
which receive all sensory impulses from the
mouth.They are called deglutition or
swallowing center.
The swallowing center specifically inhibits the
respiratory center.
OESOPHAGEAL AND STOMACH FUNCTIONS
OEASOPHAGEAL SWALLOWING - 2 types of peristaltic movements
Primary peristalsis - continuation of the wave that begins in the pharynx
Secondary peristalsis - results from the distension of oesophagus by the
retained food. It is initiated by intrinsic neural circuits in the oesophageal
myenteric nervous
.
RECEPTIVE RELAXATION OF THE STOMACH - the entire stomach and also
duodenum became relaxed as the peristaltic oeasophageal wave reaches
the lower part of oesophagus, and thus are prepared to receive the food
propelled down.
When the peristaltic swallowing wave passes down the oesophagus, the
”receptive relaxation” relaxes also easophageal sphingter, which allows
easy propulsion of the food. The easophageal sphingter is tonically
contracted to prevent the reflux of the acidic content of the stomach. Another
factor to prevent reflux is a valve-like mechanisms of the short portion of
oesophagus that lies beneath the diaphragm before reaching the stomach.
FUNCTIONS OF THE STOMACH
MOTOR FUNCTION
1) storage of large quantities of food
until processed in the duodenum
2) mixing of this food, propulsion,
retropulsion, with gastric
secretion until it forms chyme
3) slow emptying of the stomach to
the small intestine at a rate
suitable for proper
digestion a absorption.
proximal
part
fundus
esophagus
curvature
minor
body
rugae
duodenum
pylorus
curvature major
antrum
(distal part)
.
When food enters the stomach, a vagovagal reflex from stomach to brain stem
and back reduces the tone of muscular
wall, and the relaxed stomach is able to
accommodate about 1.5 L of food.
Mixing of food with digestive juices is
performed by mixing waves moving
towards the antrum. The waves are
initiated by the basic electrical rhythms
and consist of slow waves. When
progressing the waves from the body to
antrum, they became more intense
providing powerful peristaltic
constrictor rings that force the antral
content towards the pylorus.
MOTOR FUNCTION OF THE STOMACH
• STOMACH has threefold motor functions:
• 1- storage of large quantities until the food can be processed in
the duodenum,
• 2- mixing the food with gastric secretion to form chyme ,
• 3- emptying of stomach into the small intestine to be properly
digested and absorbed.
• The emptying of the stomach is regulated by excitatory effect of
gastrin on its peristalsis. But mainly by feedback signals from the
duodenum that includes both enterogastric nervous and hormonal
feedback. The rate of stomach emptying is limited by the amount of
chyme to be processed in small intestine.
FUNCTIONS OF THE STOMACH
EMPTYING
is promoted by the intense peristaltic contractions of the stomach antrum.
After the mixing of the content of stomach by the slow waves, they become intense
beginning in the midstomach and spreading throughcaudal stomach as strong
peristaltic tight ring-like constrictions. The intensity of the antral peristalsis is the
factor determining the rate of stomach emptying. The peristaltic waves provide a
pumping action called pyloric pump. In the pylorus the thickness of the circular
muscle becomes grater than in earlier portions of the antrum and remains tonically
contracted. This site is called pyloric sphincter. It prevents passage of food
particles until they are completely mixed in the chyme to fluid.
The rate at which stomach empties is regulated by signals from stomach and
duodenum.
Gastric factors- the increased food volume in the stomach promotes its emptying.
Stretching the stomach wall does elicit local myenteric reflexes that excite the
pyloric pump and decrease the activity of pyloric sphingter.
Gastrin (hormone produced by the antral mucosa) has a mild activation effect on
motor function of the stomach.
SUMMARY OF THE CONTROL OF STOMACH EMPTYING
•
•
•
(1)
(2)
Emptying of the stomach is controlled only to a moderate degree by
stomach factors such as filling, and the excitatory effect of gastrin
on its peristalsis
The more important control of stomach emptying resides in
feedback signals from the duodenum including both the
enterogastric nervous system feedback reflexes and hormonal
feedback.
These two mechanisms work together to slow the rate of emptying
when
Too much chyme is already in the small intestine or
the chyme is excessively acid, contains too much unprocessed
protein or fat, is hypotonic, or hypertonic or is irritating.
In this way the rate of stomach emptying is limited to that amount of
chyme that the small intestine can process
SECRETORY FUNCTION
Secretory glands have two main functions:
First, they secrete digestive enzymes located from the mouth to the distal end of
the ileum.
Second, mucous gland provide mucus for lubrication and protection of the tract.
They are located from the mouth to the anus.
Types of glands:
1) Single cell – mucous cells (goblet cells) produce mucus in response to local
stimulation
2) Crypts of Lieberkühn representing invagination of epithelium into submucosa
3) tubular glands typically in the stomach acid and pepsinogen secreting glands
4) complex glands, salivary glands, pancreas, liver. They contain acini lined with
sereting cells which feed into as system of ducts. These are located outside the
walls of the alimentary tract.
SYNTHESIS AND SECRETION OF
ENZYMES/PROTEINS IN THE SECRETORY GLANDS
SALIVARY GLANDS
Secretion:
enzyme ptyalin - alpha-amylase for digesting starches (submandibular, and sublingual
glands).
mucus for lubrication and protection ( parotid gland)
Saliva contains several factors to destroy bacteria: thiocyanate ions, lyzozymes,
antibodies .Saliva contains potassium and bicarbonate ions, that is less than in plasma.
Primary secretion
1. amylase
2. mucus
Volume: 0.8-1.5 L/d
0.5 ml/min
active resorption Na+
active secretion K+
passive resorption Clsecretion of HCO3and water
Saliva
EBNER GLANDS
Serous salivary glands which reside adjacent to the
posterior one-third of the tongue.
They digest about 30 % of triglycerides present in food
NERVOUS REGULATION OF SALIVARY SECRETION
.
mainly para-sympathetic nervous signals from the salivatory nuclei in the
brain stem (located at the junction of the medulla and pons). They are
activated by taste and tactile stimuli from the tongue.
Sympathetic stimulation can also, to a moderate degree, activate salivation.
These nerves originate in the superior cervical ganglia and travel along
the blood vessels to the salivary gland.
Blood supply to the salivary gland is important factor to affect salivary
secretion.
Steroid hormone from adrenal cortex testes, or ovaries can be detected in
saliva.
OESOPHAGAL SECRETION – only mucous glands. Mucus protect
oesophagus from digestion by gastric juices that may reflux from the
stomach.
LUBRICATING AND PROTECTIVE PROPERTIES OF MUCUS
Mucus is a thick secretion composed mainly of water, electrolytes, and a
mixture of several glycoproteins, which are composed of large polysaccharides bound with much smaller quantities of protein.
Mucus is an excellent lubricant and protectant for the wall of the gut.
• Mucus has adherent qualities to adhere tightly to the food and other
particles
• Mucus has sufficient body that it coats the wall of the gut and prevent
contact of food articles with the mucosa.
• Mucus has a low resistance for slippage; the particles can slide along
the epithelium
• Mucus causes fecal particles to adhere to one another
• Mucus is resistant to digestion by the GIT enzymes
• Mucus glycoproteins have amphoteric properties, i.e. they are capable
of buffering small amounts of acids or alkalies.
GASTRIC SECRETION
The stomach mucosa has, in addition to mucus secreting cells, two types of glands:
Oxyntic glands – secrete HCl, pepsinogen, intrinsic factor, and mucus.
Pyloric glands – secrete mucus (to protect pyloric mucosa), gastrin and
pepsinogen,
(HCl
)
pepsinogen
Oxyntic gland of the stomach
Schematic anatomy of the canaliculi of
oxyntic (parietal) glands
POSTULATED MECHANISMS FOR THE SECRETION OF HCl
(pH=0.8)
Cl– ions are actively transported from parietal cells into canaliculi, Na+ ions are
actively transported out of the lumen. As a response passive diffusion of K+ ions into
the canaliculus.
Water dissociates, and H+ ions are actively exchanges for K+ ons in the canaliculi
Na+ ions are actively reabsorbed, thus the majority of K+ and Na+ ions are reabsorbed,
H + ions take their place. Water passes into canaliculi by osmosis.
CO2 formed during metabolism combines under the influence of carbonic anhydrase
with OH– ions to form HCO– 3 ions, which are transported out of the cell.
REGULATION OF GASTRIC SECRETION
Direct stimulation of gastric glands:
ACETYLCHOLINE – excites secretion by all secretory cell types (enhances
secretion of pespinogen, HCl, mucus) Cholinergic nerve signals originate in
the vagus, pass to the enteric nervous system of the stomach wall and than
to the gastric glands. Cholinergic signals activating gastrin act via gastrin
releasing peptide -bombesin
HISTAMINE - mainly secretion of HCl. Small tonic secretion oh histamin is
present in gastric mucosa
GASTRIN – is absorbed into blood, carried to oxyntic glands to stimulate HCL
secretion
Multiplicative effect of acetylcholine, gastrin, and histamin: the activity
of all three substances is higher than additive. They potentiate each others´
effects
PHASES OF GASTRIC SECRETION
Cephalic phase – occurs before the food
enters stomach. It results from smell, sight,
thought… Neurogenic signals that cause
cephalic phase originate in the cerebral cortex,
and apetite centers (amygdala, hypothalamus).
Transmission through vagus. ~20% of gastric
secretion assoc. with meal.
Gastric phase – food in the stomach excites
the long vago-vagal reflexes, gastrin
mechanisms. ~70% of gastric secretion
associated with eating the meal.
Intestinal phase – food in the upper
portion of small intestine (duodenum)
activates gastrin mechanisms. Inhibitory
mechanisms result from 1) enterogastric
reflex transmitted through enteric nervous
system, and 2) activation of inhibitory
hormones gastric inhibitory peptide,
vasoactive inestinal polypeptide and
somatostatin
PANCREAS
gallbladder
bile
duct
pancreas
additional
Santorini duct
papilla of
Vater
pancreartic duct
PANCREATIC SECRETION
In addition to the secretory activity of Langerhans islets (glucagon and insulin), the
pancreatic acini secrete digestive enzymes:
chymo-trypsin(ogen), trypsin(ogen), that catalyze cleavage of partially digested
proteins into peptides
trypsin inhibitor to inhibit cleavage of chymo-trypsinogen and trypsinogen
carboxypolypeptidase splits some peptides into aminoacids.
Pancreatic amylase, hydrolyses starches, glycogen, and other carbohydrates
(except for cellulose) to form disaccharides
pancreatic lipase that hydrolyses neutral fats into fatty acids and monoglycerides,
cholesterol esterase that hydrolyses cholesterol esters,
phospholipase that splits fatty acids from phospholipids. At the same time trypsin
inhibitor is secreted to protect the pancreatic cells from digestion by trypsin.
Epithelial cells from the duct leading from acini secrete bicarbonate ions.
SECRETION OF BICARBONATES BY PANCREATIC
DUCTULES
REGULATION OF PANCREATIC SECRETION
LIVER SECRETION OF BILE
Liver among its many functions produces and secretes bile between 600 and
1200 mL/day. It has two major functions:
FIRST fat digestion and absorption because of the bile acids. These –
1) help to emulsify the large fat into small particles that can be digested by the
lipase enzyme secreted by pancreas.
2) help to the transport and absorption of digested fat products to the intestinal
mucosa.
SECOND bile serves for excretion of waste products from the blood especially
bilirubin and excess of cholesterol produced by the liver.
Bile is secreted by the liver in two stage: hepatocytes produce bile components
which are secreted into canaliculi, and subsequently into bile duct, where
HCO-3 ions and water are added. The epithelial cells secretion is activated by
SECRETIN
Bile secreted by the liver is stored in gallbladder (30 – 60 ml). Water, sodium,
chloride are absorbed by gallbladder mucosa, bile is more concentrated.
COMPOSITION OF BILE
BILE (SALT) ACID
BILE SALTS:
hydrophobic centers
and polar group at
the surface – water soluble
LIVER SECRETION AND GALLBLADER EMPTYING
SUMMARY
1. Movement of food through alimentary tract is supported by :
a)
Intrinsic activity of enteric nervous systém, mainl\y by myenteric plexus
b)
gastrointestinal reflexes from GIT to prevertebral ganglia, or brain stem
2. Secretory activity of GIT:
a)
all parts of GIT secrete mucus
b)
saliva contains alpha- amylase (salivary glands), lipase (Ebner glands), HCO– 3
(ducts)
c)
stomac secrets gastrin (pyloric glands), HCl, intrinsic factor, pepsinogen (oxyntic
glands)
d)
pancreas secrets pancreatic amylse, trypsynogen, chymotr\ypsynogeb,
procarboxypolypeptidase, trypsin inhibitor, lipase (acinar cells) , HCO– 3 (ducts)
e)
liver secrets bile acids (to emulsify fat), cholesterol, phospholopids (to form
micelles)
Pancreatic products and bile are emptied to duodenum through papilla of Vater