Digestive System - Physiology

Digestive SystemDigestive System
PhysiologyPhysiology

The digestive system is formed of
1. Alimentary canal
2. Digestive glands

 Mucosa
 submucosa
 circular m layer
 longtudinal m layer
 serosa
Structure of alimentary canalStructure of alimentary canal

Types of movement of GIT
Peristalsis
Stretch circular contraction behind & relaxation in front→
Stretch serotonin sensory nerves myenteric plexus→ →
-Retrograde cholinergic neurons (subs P & a.ch) →
contraction
-Antegrade cholinergic neurons (VIP, NO & ATP) →
relaxation
Mixing movement
•Peristaltic wave in blocked sphincter
•Constrictive movement

Innervation of the GIT
1. Intrinsic innervation: Enteric Nervous
System.
2. Extrinsic innervation: Parasympathetic
and sympathetic innervations.

 Myenteric plexus (Auerbach's plexus).
 Submucous plexus (Meissner's
plexus).
Enteric nervous systemEnteric nervous system

Submucous plexus Myenteric plexus
between the circular
layer and the mucosa.
between the outer
longitudinal and inner
circular muscle layers
Exocrine and endocrine
functions of the GIT
Motor function of the
GIT
Mainly excitatory,
some inhibitory
Enteric nervous systemEnteric nervous system

 The plexuses are interconnected.
 They contain motor neurons; secretory neuron
sensory neurons that respond to stretc
tonicity, glucose, or amino acids; an
interneurons.
 Substances secreted by the ENS: acetylcholin
serotonin, GABA, and vasoactive intestin
peptide.

2. Extrinsic Innervation:
 Parasympathetic:
Cranial (Abdominal
viscera)
Preganglionic : vagus
Relay: terminal
ganglia on the wall
of the viscera
Postganglionic : in
the myenteric and
submucosal plexus
Sacral:2nd
, 3rd
, 4th
(pelvic
viscera)
Preganglionic : pelvic
nerves.
Relay: terminal ganglia
on the wall of the viscera
Postganglionic ends on :
in the myenteric and
submucosal plexus
Increase in the activity of ENS

2. Extrinsic Innervation:
 Sympathetic:
(Abdominal viscera)
Preganglionic : lower 6th
thoracic
Run as greater splanchnic nerve.
Relay: coeliac and superior
mesenteric ganglia
Postganglionic: pass with blood
vessels to all parts of the gut
(Pelvic viscera)
Preganglionic : T12 , L1, 2, 3.
Run as lesser splanchnic nerve.
Relay: inferior mesenteric ganglia
Postganglionic: pass with blood
vessels to all parts of the gut
Inhibition of GIT function: directly
Inhibition of enteric nervous system

Regulation of the GIT
1. Nervous control of GIT:
 Reflexes that occur inside the ENS: self regulation
(local enteric reflexes)
 Reflexes from the gut to symp ganglia then back to GIT
(enterogastric reflex)
 Reflexes from the gut to parasymp n. in BS or sc back
to GIT (conditioned and unconditioned reflexes).

2. Hormonal control:
Polypeptides secreted by APUD cells (amine precursors
uptake and decarboxylation).
Hormones fall into one of 2 families:
Gastrin family: the primary members of which are
gastrin and cholecystokinin (CCK).
Secretin family: the primary members of which are
secretin, glucagon, VIP, and gastrin inhibitory
polypeptide (GIP).
Others: motilin and somatostatin

Mastication (Chewing)Mastication (Chewing)
•Mechanical breakdown
of large food particles into
smaller ones in the mouth.
•Increase exposed surface
area to enzymes and help
swallowing.

 Center: pons
 Mastication muscles: motor branch of trigeminal.
 May be voluntary or involuntary (autonomic reflex)
Mastication (Chewing)Mastication (Chewing)

Swallowing (Deglutition)Swallowing (Deglutition)
•Propelling of food from mouth to
stomach through pharynx and
oseophagus

Salivary Secretion
Saliva is secreted primarily by three pairs of glands:
1. the parotid glands: 20%
2. the submandibular: 75%.
3. the sublingual glands: 5%.
4. many small buccal glands in mouth cavity.

99.5% water
0.5% Solids: a. organic: K+
, Na+
, HCO-
3, Cl-
,
Na2HPO4.
b.Organic: Ptyalin enzyme
Mucin
Lysozymes
Immunoglobulin A
Composition of saliva: 1500ml/dayComposition of saliva: 1500ml/day

Salivary Secretion
Saliva
•800- 1500 ml/day with proteins & electrolytes
•pH→ 6- 7.0 ( 8.0 during active secretion)
•Hypotonic ( Na+
& Cl-
less , K+
& HCO3 more than plasma
•Contains
IgA,
lysozyme,
lactoferrin,
mucin
prolin rich proteins

 The parotid glands acini are serous.
 The sublingual glands acini are mucous.
 The submandibular glands acini are mixed.
 The buccal glands secrete only mucous.
Types of Salivary glands:Types of Salivary glands:

Stages of Salivary Secretion:
I-Primary secretion in the acini:
contains ptyalin and/or mucin in a solution of ions which shows no
great difference from extracellular fluid.
II- Modification of Primary secretion in the ducts: the
following occur under effect of aldosterone.
Sodium ions (Na+) are actively reabsorbed.
Potassium ions (K+) are actively secreted.
Sodium reabsorption is higher than potassium secretion in the
salivary ducts
Chloride ions (Cl-) to be passively reabsorbed.
Therefore, the sodium ion and chloride ion concentrations of the
saliva are markedly reduced whereas the potassium ion
concentration becomes increased during passage through the ducts.

 Bicarbonate ions (HCO3-
) are actively secreted into
the lumen of the duct.
 The ducts are relatively impermeable to water.
Therefore, the saliva that reaches the mouth is
hypotonic and alkaline (pH= 8.0).

Functions of Saliva:
Protection of oral mucosa:
 Cooling hot foods.
 Neutralizing acid.
 Lysozyme attacks the walls of bacteria.
 Antibodies (immune globulin IgA) destroy
oral pathogenic bacteria.

Teeth protection:
 The buffers in saliva: bicarbonate, phosphate buffers,
mucin, help to keep the oral pH at about 7.0. At this
pH, the saliva is saturated with calcium and so the
teeth do not lose calcium. Loss of Ca2+
from the teeth
enamel leads to dental caries.
Digestion:
 Saliva contains the digestive enzyme ptyalin
(salivary α-amylase) that digests starch into
disaccharides.

 Lubrication and Wetting:
 Swallowing: Saliva contains mucin
(glycoproteins) that lubricates the
food
 Speech: Keeping mouth moist
facilitates movements of the lips and
tongue during speech.
 Taste: Saliva acts as (a solvent for the
molecules that stimulate taste receptors.

Innervation of salivary glands
Parasympathetic efferent
Increase secretion & VD ( Ach & VIP)
Sublingual & submandibular glands
Superior salivary nucleus →facial ( corda tympani)
Parotid gland
Inferior salivary nucleus → glossopharyngeal nerve

Sympathetic efferent
Small amount of saliva rich in organic
constituents- VC
Superior & inferior salivary nuclei → T 1 & 2
→ superior cervical ganglion → all salivary
glands
Both sympathetic & parasympathetic are
complementary in salivary secretion

Submandibular
and sublingual
Parotid gland
Superior salivary
nucleus in medulla
inferior salivary
nucleus in medulla
Preganglionic
fibers arise
Chorda tympani
(facial)
Glossopharyngeal
n.
Run as
Submandibular
ganglon
Otic ganglion relay
Supply
Submandibular and
sublingual
Supply parotid
gland
Postganglionic
fibers
Innervation of salivary glands:Innervation of salivary glands:
parasympathetic fibersparasympathetic fibers

Sympathetic efferent fibres:
 Preganglionic fibres arise from the lateral horn cells of
the upper 2 thoracic segments of the spinal cord.

 They relay in the superior cervical ganglion.
 Postganglionic fibres arising from this ganglion reach
all the salivary glands along the wall of their blood
vessels.
 Stimulation of the sympathetic nerve supply to the
salivary glands causes vasoconstriction, and secretion
of a small amount of saliva rich in mucin.

Control of Salivary secretion:
 Stimulation of salivary secretion is entirely
under neural control in response to conditioned
or unconditioned stimuli.

Unconditioned reflexes:
Mechanical and chemical stimulation of taste
buds in mouth causes reflex secretion of large
amount of watery saliva:

Conditioned reflexes:
 Salivary secretion is easily conditioned as
shown in Pavlov's original experiment. Sight,
smell, hearing, preparation of food, or even
thinking of food, result in reflex increase in the
secretion of saliva. The impulses arrive to the
salivary nuclei from the cerebral cortex, in
response to any conditioned stimulus.

Swallowing (Deglutition)Swallowing (Deglutition)
•Buccal (oral phase)
•Pharyngeal phase
•Oesophageal phase.
Involuntary
Voluntary

 Tongue is elevated upwards and backwardsTongue is elevated upwards and backwards
with bolus of food on its dorsum.with bolus of food on its dorsum.
 Bolus of food is rolled backwards to back ofBolus of food is rolled backwards to back of
tongue.tongue.
 Bolus is forced to pharynx by contraction ofBolus is forced to pharynx by contraction of
mylohyoid muscle.mylohyoid muscle.
Buccal phaseBuccal phase

 Receptor:Receptor: swallowing receptor area on theswallowing receptor area on the
tonsillar pillars at the oropharyngealtonsillar pillars at the oropharyngeal
junction.junction.
 Afferent:Afferent: glossopharyngeal nerve.glossopharyngeal nerve.
 Centre:Centre: swallowing centre in medulla andswallowing centre in medulla and
lower pons.lower pons.
 Efferent:Efferent: 55thth
, 9, 9thth
, 10, 10thth
, 12, 12thth
nerves.nerves.
Pharyngeal phasePharyngeal phase

 Actions:Actions:
1.Rapid peristaltic1.Rapid peristaltic
wave:wave: cont. of superior,cont. of superior,
middle & inferiormiddle & inferior
pharyngeal muscles.pharyngeal muscles.

 Actions:Actions:
2. Protective reflexes:2. Protective reflexes:
 Nose: elevation of soft palateNose: elevation of soft palate
 Mouth: elevation of tongue, cont. of myelohyoid muscle.Mouth: elevation of tongue, cont. of myelohyoid muscle.
 Larynx: elevation of larynx to be covered by epiglottis,Larynx: elevation of larynx to be covered by epiglottis,
inhibition of respiration.inhibition of respiration.

Actions:Actions:
3. Relaxation of pharyngeoesophageal sphincter3. Relaxation of pharyngeoesophageal sphincter
Opening way for bolus of food to oesophagusOpening way for bolus of food to oesophagus

Swallowing ( deglutition)
Oral voluntary stage
Food is rolled posteriorly by pressure of tongue upward
Pharyngeal stage ( involuntary)
Soft palate close nares , vocal cords approximate
Epiglottis close larynx, upper esophageal sphincter relaxes,
pharynx contract( peristalsis) -respiration stops
Esophageal stage ( involuntary)
Primary peristalsis→ pharynx to stomach
Secondary peristalsis from distention of esophagus by food
( enteric nervous system & vago-vagal reflex)

Peristaltic waves:Peristaltic waves:
1. 1ry peristaltic wave:1. 1ry peristaltic wave:
Continuation of peristaltic wave in pharynx.Continuation of peristaltic wave in pharynx.
Start in upper part of oesophagus and travels wholeStart in upper part of oesophagus and travels whole
length in 9 sec.length in 9 sec.
Oseophageal phaseOseophageal phase
If failedIf failed
2ry peristaltic wave2ry peristaltic wave

Peristaltic waves:Peristaltic waves:
2. 2ry peristaltic wave:2. 2ry peristaltic wave:
As a result of distension of oesophagus by retainedAs a result of distension of oesophagus by retained
food (bolus).food (bolus).
A 2ry wave at site of bolus empty all contentsA 2ry wave at site of bolus empty all contents
into the stomachinto the stomach..
Oseophageal phaseOseophageal phase

 Upper half of oesophagus: vagovagal reflex.Upper half of oesophagus: vagovagal reflex.
Bilateral vagotomy: ???Bilateral vagotomy: ???
 Lower half of oesophagus: local reflex.Lower half of oesophagus: local reflex.
Control of oseophageal phaseControl of oseophageal phase

Oesophageal musclesOesophageal muscles

Lower Esophageal Sphincter
LES
• Remains tonically contracted
• Receptive relaxation (relaxes LES ahead of
peristaltic waves) → easy propulsion
• Between meals LES prevent reflux of gastric
content into esophagus
• Tone of LES
Ach→ contraction of LES
NO & VIP → relax LES
• ↓ tone of LES → gastro esophageal reflux

 It is a physiological sphincter at the lowerIt is a physiological sphincter at the lower
end of oesophagus.end of oesophagus.
 Tonically contracted to prevent regurgitationTonically contracted to prevent regurgitation
of acidic gastric contents to oesophagus.of acidic gastric contents to oesophagus.
 During swallowing, it relaxesDuring swallowing, it relaxes
Lower Oesophageal sphincter (LES)Lower Oesophageal sphincter (LES)

- Parietal cells
secret HCl & intrinsic factor
- Cheif cells
secret pepsinogen
- Entero-Chromafin-Like
cells
secret histamin
-mucous cells

 FundusFundus
 BodyBody
 AntrumAntrum
 PylorusPylorus
Stomach is divided anatomicallyStomach is divided anatomically

Cardia
Lesser curvature
Duodenum
Pylorus
Esophagus Fundus
Body
Greater
curvature
Antrum

Function of the StomachFunction of the Stomach
1.Motor function of stomach
2.Secretory function of stomach

Secretory function of stomachSecretory function of stomach
Gastric
gland

 H2OH2O
 Ions:Ions: HH++
, Cl, Cl--
, Na, Na++
, K, K++
 Enzymes:Enzymes: pepsin, gelatinase, lipasepepsin, gelatinase, lipase
 MucousMucous
 Intrinsic factorIntrinsic factor
Composition of acid secretionComposition of acid secretion

Acid secretionAcid secretion
H2O
OH-
H2O
1
2
3
5
4
6 7
8

Acid secretionAcid secretion
1
2

Functions of HCl
• Killing bacteria
• Dissolve food into chyme
• Activate pepsinogen
• Iron & calcium absorption
• Stimulate secretin hormone & bile flow

Stimuli of HCl secretion:
• Histamine: acts via H2 receptors
increases intracellular cAMP.
• Acetylcholine: acts via M3 muscarinic
receptors increases intracellular Ca+
+.
• Gastrin: it acts either directly on
oxyntic cells by increasing
intracellular Ca++ (like acetylcholine)
or indirectly through stimulating the
secretion of histamine from
enterochromaffin-like cells (ECL

Mechanism of action of HCl stimuli:
•Parietal cells contain receptors for
these stimuli. Binding of these stimuli
with their receptors release 2nd
messengers which transfer the H+/K+
ATPase proteins from the membranes
of intracellular vesicles to the plasma
membrane thus increasing the number
of pump proteins in the plasma
membranes.

 Acetyl choline.Acetyl choline.
 Gastrin hormone.Gastrin hormone.
 HistamineHistamine.
Stimulation of acid secretionStimulation of acid secretion

Phases of gastric secretionPhases of gastric secretion
Cephalic phase ( nervous)-
Condition & unconditioned reflexes → vagus nerve → acetylcholine & gastrin
→ ↑HCl, pepsinogen & mucous ( one third of secretion)
Gastric phase ( nervous & hormonal) 2/3 of secretion
Long vagovagal reflexes
Local enteric relexes
Gastrin secretion
Intestinal inhibitory phase ( nervous & hormonal)
Presence of food in intestine → entero gastric reflex & secretion of GIP, VIP,
CCK & secretin which inhibit secretion

Cephalic phase: (nervous):Cephalic phase: (nervous):
Conditioned & unconditionedConditioned & unconditioned
Gastric phase: (nervous and hormonal):Gastric phase: (nervous and hormonal):
Vagovegal reflexVagovegal reflex
Local enteric reflexesLocal enteric reflexes
Gastrin mechanismsGastrin mechanisms
Intestinal phase: (nervous and hormonal):Intestinal phase: (nervous and hormonal):
Entergastric reflexEntergastric reflex
Hormones: GIP, VIP, CCK, secretinHormones: GIP, VIP, CCK, secretin
Regulation of acid secretionRegulation of acid secretion

Gastric motility
Physiologically- based the stomach is divided
into
- Proximal motor unit ( fundus & body)
responsible for storage of food ( receptive
relaxation)
- Distal motor unit ( antrum & pylorus)
responsible for
• mixing & partial digestion of food
• gastric peristaltic waves & emptying food

1- storage function of stomach ( receptive
relaxation)
Gastric distention relaxation of stomach to→
increase capacity to 1- 1.5 L from 50 ml
( efferent fibers in vagus, sympathetic & ENS)
2- Mixing & propulsion of food
Gastric slow waves start at mid point of greater
curvature ( 3-5 cycles/min) spiks peristaltic→ →
waves contraction of antrum followed by pyloric→
region & duodenum
3- stomach emptying

Regulation of gastric evacuation
1- gastric factors
Distention of stomach & gastrin hormone increase→
gastric emptying
2- intestinal factors
Enterogastric relex ( acid, irritation, distention, fats &
proteins inhibit gastric emptying→
Fat in duodenum CCK, GIP & secretin inhibit→ →
gastric emptying
3- Liquids are evacuated more rapidly, carbohydrates
more than fats or proteins
4- Pain inhibits & emotions increase or decrease
gastric emptying

 Proximal motor unit:Proximal motor unit: fundus bodyfundus body
 Distal motor unit:Distal motor unit: Antrum PylorusAntrum Pylorus
Stomach is divided physiologicallyStomach is divided physiologically

Innervation of the Stomachnnervation of the Stomach
 1. Parasympathetic (vagus nerve):
Cholinergic
excitatory fibers
•Distal motor unit
Purinergic
inhibitory fibers
• Proximal motor
unit

Innervation of the Stomachnnervation of the Stomach
2. Sympathetic Fibers:
 Origin: Lower 6th
thoracic segments
 Preganglionic: greater splanchnic nerve.
 Relay in: Celiac ganglion
 Postganglionic: pass to stomach to inhibit PMU

1.Motor function of stomach1.Motor function of stomach
 Storage of food.
 Mixing and partial digestion of food to form
chyme.
 Slow empting of the chyme into duodenum.

1.Motor function of stomach1.Motor function of stomach
Storage of food (receptive relaxation):
Reflex initiated by the arrival of food into the stomach to increase its capacity for food.
50ml 1-1.5L (So stomach bulge outwards while pressure remains low).

Storage of food (receptive relaxation):Storage of food (receptive relaxation):
Gastric distension.
Afferent fibers
Vagal nucleus Sympathetic ganglia Local enteric plexus
Purinergic
vagal fibers
Myenteric
inhibitory
fibers
Adrenergic
sympathetic

Motor function of stomachMotor function of stomach
2. Mixing of food and empting of stomach:
Weak peristaltic wave start in the middle of the body towards pylorus (stronger and faster at pyloric antrm).
Antral contents to be forced back to the proximal part leads to mixing of food

Antrum, pylorus and upper duodenum function as one unit contraction of
antrum followed by contraction of pylorus and duodenum gastric contents
prevented from entering duodenum but mixed and crushed.

Strong peristaltic
wave at pylorus
(pyloric pump)
Toniccontractionof
pyloricsphincter
Slow gastric emptingSlow gastric empting

Factors affecting gastric empting:
1. Gastric factors:
Gastric distension Gastric empting
( ++ Pyloric pump , -- pyloric sphincter)
 Nervous reflexes
 Gastrin hormone

2. Intestinal factors (entergastric reflex):
Presence of the following factors inhibits gastric
empting (-- pyloric pump, cont. pyloric
sphincter):
 fats and proteins.
 Increased pH.
 Distension of duodenum.

Entergastric reflexEntergastric reflex
Fats and proteins.
Increased pH.
Distension of
duodenum.
Afferent fibers
Vagal
nucleus
Sympathetic ganglia
Purinergic vagal
fibers
Adrenergic
sympathetic
Secretin
CCK
GIP
Secretin
CCK
GIP

3.Consistency of food:
Liquids > solids

Vomiting
Reflex abnormal emptying of gastric content
through esophagus & mouth
Causes of vomiting
1.Reflex mechanical stimulation of posterior→
tongue – irritation of gastric mucosa- intestinal
obstruction- sever pain – coronary thrombosis
2.central stimulation of CTZ by drugs,→
hypoxia, acidosis, morning sickness of
pregnancy & motion sickness

Mechanism of vomiting
- Relaxation of stomach & LES – contraction
of pyloric sphincter
- Deep inspiration , strong contraction of
diaphragm& abdominal muscles to increase
intra-abdominal P squeeze the contents of→
stomach up
- Protection of air passages

Pancreatic secretion
It is the most important digestive juice
because it contains enzymes for
digestion of most of food stuffs
• Volume → 1500 ml / day
• pH → 8-8.3, Alkaline ( HCO3)
• Pancreatic Digestive enzymes

Pancreatic Digestive enzymes
1. Proteolytic enzymes trypsin,
chymotrypsin, carboxypeptidase,
ribonuclease & deoxyribonuclease
2. Pancreatic amylase
3- Pancreatic lipase.
4- cholesterol esterase
5- phospholipase

Regulation of pancreatic secretion
Nervous regulation
Vagal stimulation (conditioned &unconditioned reflex)
→ acetyl choline → pancreatic enzymes
Hormonal regulation
Secretin
Acid in intestine → secretin → pancreatic juice rich in
HCO3
Cholecystokinin CCK
Polypeptides, amino acids & fats → CCK → pancreatic
juice rich in enzymes

Functions of the liver
Liver acts as a chemical factory, an
excretory system, an exocrine and
an endocrine gland
1- Vascular Functions for Storage and
Filtration of Blood:
store 200-400 ml. of blood
Kupffer cells(remove 90% of bacteria in the
portal venous blood (the colon bacilli)

2- Metabolic Functions:
Carbohydrate metabolism: (glucostat" )
Glycogenesis- glycogenolysis- gluconeogenesis- Cori cycle
( formation of glycogen from lactic acid)
Lipid metabolism:
oxidation of fatty acids - Formation of lipoproteins - lipogenesis
Protein metabolism:
Deamination of amino acids - Formation of urea , plasma proteins,
most of coagulation factors & non-essential amino acids
Storage of vitamins: Such as vitamin A, D, E, K and B12. &
iron
Detoxification or excretion of drugs, hormones and
other substances

3- Secretory and excretory functions:
Formation of bile:
• Bile is required for the digestion and
absorption of fats ( bile salts) and for the
excretion of water-insoluble substances such
as cholesterol and bilirubin
• Secretion is continuous through all the day &
is stored in gall bladder

Composition of bile
• 500-1500 ml/day
• Fresh bile is alkaline
• Becomes acidic during storage in gall
bladder to prevent precipitation of
calcium

Water 97.00 %
Bile salts 0.70 %
Bile pigments 0.20 %
Cholesterol 0.06 %
Inorganic
salts
0.70 %
Fatty acids 0.15 %
Lecithin 0.10 %
Fat 0.10 %

Bile salts•
sodium and potassium salts of bile acids
conjugated to glycine or taurine
( glycocholic & taurocholic acids)
- The bile acids are synthesized from cholesterol.•
– Primary bile acids:
cholic acid and chenodeoxycholic acid.•
– Secondary bile acids:
In the colon, bacteria convert cholic acid to
deoxycholic acid and chenodeoxycholic acid to
lithocholic acid.

Function of bile salts
1- Digestion of fat
a-activation of pancreatic lipase
b- emulsification of fat preparatory to its
digestion and absorption by
- detergent action reduce surface→
tension between fat globules
- hydrotropic action

2-Absorption of fat & fat soluble
vitamins- form micelles
micelles are bile acid-lipid water-soluble
complexes that play an important role in
keeping lipids in solution and transporting
them to the brush border of the intestinal
epithelial cells, where they are absorbed.

Phospholipids
Free fatty acids, cholesterol
Bile acids
Bile acids
OH group
Peptide bond
Carboxyl group

The Gallbladder

Functions of the Gallbladder:
Storage of Bile
Concentration of Bile
removal of sodium by the gallbladder
mucosa through an active transport
mechanism, which passively draws chloride,
bicarbonate and water.
Prevention of marked rise in the
Intrabiliary pressure
Secretion of white bile
Acidification of Bile: (absorption of
bicarbonate)

Control of Gallbladder Emptying =
Cholagogues
Cholecytokinin (CCK)
major stimulus for gallbladder contraction
and sphincter of Oddi relaxation.
Vagal stimulation
cephalic stage of digestion and vago-vagal
reflex during the gastric phase of digestion

Movement of small intestine
Segmentation movements & peristalsis help
mixing & propagation of the contents down the
intestine
1- Segmentation ( mixing) contractions
Divide the chyme, increase blood &lymph fow & mix food
with secretion
Duodenum & jejunum → 12/min
Ileum → 8-9/min
Controlled by slow wave ( basic electrical rhythm – myenteric
nerve plexus)

2- Peristalsis
• Faster in proximal part & slower in distal part
• Progression of the chyme 1-2 cm/min ( 3-5hr for
travel from pylorus to ileocecal valve)
Stretch contraction behind (subs P &→ →
a.ch) & relaxation in front VIP, NO & ATP→
• Increased after meal by stretch of
duodenum, gastro enteric reflex & hormones
(gastrin- CCK-insulin
• Inhibited by secretin & glucagone

Digestive System - Physiology

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