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DIGESTIVE PHYSIOLOGY
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FUNCTIONS OF THE
DIGESTIVE SYSTEM
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ORAL CAVITY
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ORAL CAVITY
PHYSIOLOGICAL EVENTS
1. Ingestion2. Mechanical digestion
3. Chemical digestion
4. Propulsion voluntary stage of swallowing
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ORAL CAVITY
Ingestion of food is
simply voluntarilytaking food into thedigestive tractthrough the oral
cavity.
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ORAL CAVITY
MECHANICAL DIGESTION
As food enters the oral cavity
the cheeks and the closed lipshold food between the teeth, thetongue mixes the food with salivato soften it, and the teeth cutand grind it into a bolus.
Mastication is both voluntary andpartly reflexive.
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ORAL CAVITY
CHEMICAL DIGESTION
Chemical digestion of starchis begun by salivary amylasepresent in saliva producedmainly by the parotid, buccal,submandibular glands.
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ORAL CAVITY
No other macromolecules are hydrolyzed withinthe oral cavity.
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ORAL CAVITY
PROPULSION
The voluntary phase ofdeglutition is initiated bythe tongue. The tip of thetongue is place on the hardpalate, and then contractswhich forces the bolusinto the oropharynx.
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ORAL CAVITY
NEUROLOGICAL CONTROL
1. Ingestion--voluntary--
2. Mechanical digestion--
3. Chemical digestion--
4. Swallowing--voluntary-
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ORAL CAVITY
HORMONAL CONTROL
NONE
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PHARYNX
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PHARYNX
PHYSIOLOGICAL EVENTS
1. Chemical digestion
2. Propulsion
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PHARYNX
Carbohydrate digestion
continues. This is due to fact that the pH of
the pharynx is slightly acid to neutral
as is the oral cavity.
No other marcomolecule beginschemical digestion.
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PHARYNX
PROPULSION
The pharyngeal phase ofdeglutition is initiated byfood in the oropharynx.The presence of foodcauses the tongue to
blocks off the oral cavity,the soft palate to rise andclose off the nasopharynx.
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PHARYNX
PROPULSION
In addition, the larynx torise so that the epiglottiscovers the opening intothe respiratory system,and the upper esophageal
sphincter to relax andopen.
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PHARYNX
NEUROLOGICAL CONTROL
Propulsion, deglutition, is involuntary
and uses cranial nerves.
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PHARYNX
HORMONAL CONTROL
NONE
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ESOPHAGUS
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ESOPHAGUS
PHYSIOLOGICAL EVENTS
1. Chemical digestion
2. Propulsion
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ESOPHAGUS
Carbohydrate digestion
continues. This is due to fact that the pH of
the esophagus is slightly acid to neutral
as is the oral cavity.
No other marcomolecule beginschemical digestion.
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ESOPHAGUS
PROPLUSION
The esophageal phase ofdeglutition begins as thebolus passes through theopen upper esophagealsphincter. The sphincter
then closed, and peristalsisdrives the bolus toward thestomach.
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ESOPHAGUS
The bolus of food ispropelled within theesophagus by peristalsis.
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ESOPHAGUS
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ESOPHAGUS
NEUROLOGICAL CONTROL
Propulsion, deglutition, is involuntary
and uses cranial nerves.
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ESOPHAGUS
HORMONAL CONTROL
NONE
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STOMACH
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STOMACH
PHYSIOLOGICAL EVENTS
1. Mechanical digestion
2. Chemical digestion
3. Propulsion
4. Absorption
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STOMACH
MECHANICAL DIGESTION
The bolus is mixedwith gastric juice
to form chyme.
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STOMACH
This is possible because ofthe 3 muscle layers of thestomach, and the contractionof the pyloric sphincter.
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STOMACH
CHEMICAL DIGESTION
The chemical digestion of
carbohydrates, whichbegin in the oral cavity,is terminated due to adecrease in pH.
The chemical digestion ofproteins begins in thestomach.
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STOMACH
Carbohydrate digestion stops, due to the decreasepH, and no lipid or nucleic acid digestion begins.
CHEMICAL DIGESTION
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STOMACH
PROPULSION
After a meal, peristalsisbegins near the cardiac regionand moves toward the pyloricsphincter. The intensity ofthe movements are due to theincrease in the number ofmuscle layers of the stomach.
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STOMACH
The pyloric region of thestomach holds about 30 mlof chyme. It allows only
liquids and small particles ofchyme, about 3 ml, to passthrough the valve for eachperistaltic wave. Thecontractions of the pylorius
decrease the opening of thevalve. This results in theremaining chyme beingremixed again and again.
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STOMACH
The rate of peristaltic wavesis constant 3/min., however,
the intensity can be modified.This contractile rhythm is setby the spontaneous activity ofpacemaker cells located in thelongitudinal smooth muscle
layer. This cells establishesthe basic electrical rhythm ofthe stomach.
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STOMACH
The stomach usuallyempties completely within
4 hours after a meal. Therate of gastric emplyingdepends on the contentsof the duodenum as on
what is happening in thestomach.
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STOMACH
ABSORPTION
1. ASPIRIN2. ALCOHOL
3. DRUGS MOSTLY FAT SOLUBLE
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STOMACH
NEUROLOGICAL CONTROL
MECHANICAL DIGESTION
1. Pace-maker cells--interstitial cells of Cajal
establish intrinsic control.2. Vagus nervecontrol mechanical digestionextrinsically.
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STOMACH
NEUROLOGICAL CONTROL
CHEMICALDIGESTION
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STOMACH
NEUROLOGICAL CONTROL
CEPHALIC PHASE
Slight, thought, taste, orsmell of food causesstimulation of the vagus.The vagus stimulates theproduction of gastricjuice.
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STOMACH
NEUROLOGICAL CONTROL
GASTRIC PHASE
Stomach distention willact locally or evoke thevagovagal reflex.
VAGOVAGAL
REFLEX
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STOMACH
NEUROLOGICAL CONTROL
CHEMICAL DIGESTION
Intestinal phase
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STOMACH
NEUROLOGICAL CONTROL
PROPULSION
1. Pace-maker cells--interstitial cells of Cajal
establish intrinsic control.2. Vagus nervecontrol mechanical digestionextrinsically.
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STOMACH
NEUROLOGICAL CONTROL
ABSORPTION
1. NONE
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STOMACH
HORMONAL CONTROL
MECHANICAL DIGESTION
1. Gastrin--stimulate gastric emptying
2. Serotonin--contraction ofsmooth muscle3. Somatostatin--inhibits motility and emptying
4. Secretin--inhibits gastric motility
5. Gastric Inhibitory Peptide--inhibits gastricmotility
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STOMACH
HORMONAL CONTROL
CHEMICAL DIGESTION
1. Gastrin--stimulates gastric secretions
2. Histamine--stimulates HCl formation3. Somatostatininhibits gastric secretions
4. Secretin--inhibits gastric secretions
5. Gastric inhibiory peptide--inhibits gastric
secretions6. Vasoactive intestinal peptide-inhibits HCl
production
STOMACH
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STOMACH
HORMONAL CONTROL
CHEMICALDIGESTION INTESTINAL PHASE
HORMONAL
CONTROL
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STOMACH
HORMONAL CONTROL
PROPULSION
1. Gastrin--stimulates emptying
2. Somatostatin--inhibits gastric motility and emptying3. Secretin--inhibits gastric motility and emptying
4. Gastric Inhibitory Peptideinhibits gastric motilityand emptying
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STOMACH
HORMONAL CONTROL
ABSORPTION
1. NONE
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LIVER GALLBLADDER
COMPLEX
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LIVER GALLBLADDER
COMPLEX
PHYSIOLOGICAL EVENTS
1. Mechanical digestion
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LIVER GALLBLADDER
COMPLEX
The liver produces bile,which is an alkalinesolution, containing bile
salts, phospholipids, andbile pigments. The liverproduces about 500 to1000 ml of bile daily. Bile
is transported to thegall bladder for storageand secretion.
LIVER
GALLBLADDER
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LIVER GALLBLADDER
COMPLEX
The gall bladder is located onthe inferior surface of theliver. It is a green muscular
sac about 4 in. in length. Thegall bladder stores bile andconcentrates it by absorbingsome of its water and ions.When it contracts bile isexpelled into the bile duct andthe duodenum.
LIVER
GALLBLADDER
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LIVER GALLBLADDER
ite of Action Enzyme Food tuff Unemulsified
Triglyceride
mall
Intestine
Bile
Emulsified
Triglyceride
MECHANICAL DIGESTION
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LIVER GALLBLADDER
NEUROLOGICAL CONTROL
The gallbladder is regulated
by the autonomic nervous
system. The parasympathetic
division, using the vagus nerve,is excitatory and
the sympathetic division
inhibits the gallbladder.
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LIVER GALLBLADDER
HORMONAL CONTROL
The liver is stimulated by
secretin to produce bilemore rapidly. Cholecysto-kinin stimulates thegallbladder to contractand hepatopancreatic
sphincter to relax, so thatbile can enter theduodenum.
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PANCREAS
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PANCREAS
PHYSIOLOGICAL EVENTS
1. Chemical digestion
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PANCREAS
The pancreas is both
and endocrine gland and
exocrine gland. The isletsof Langerhan are endocrineand the acinar cells formthe exocrine portion.
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PANCREAS
The pancreatic juice,produced by the acinarcells, moves from the
pancreas to the duodenumin the pancreatic duct.
Pancreatic juice consistsmainly of water, enzymes,
and bicarbonate ions. ThepH is alkaline which helps toneutralize the acid chyme.
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PANCREATIC JUICE
PANCREATIC JUICE
1. Pancreatic amylase2. Pancreatic lipase
3. Pancreatic ribonuclease & deoxyribonuclease
4. Trypsin, chymotrypsin, carboxypolypeptidase
5. Bicarbonate ions
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PANCREAS
CHEMICAL DIGESTION
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PANCREAS
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PANCREAS
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PANCREAS
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PANCREAS
NEUROLOGICAL CONTROL
The pancreas is regulated
by the autonomic nervous
system. The parasympathetic
Division, using the vagusnerve, is excitatory and
the sympathetic division
inhibits the pancreas.
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PANCREAS
HORMONAL CONTROL
The pancreas is regulatedhormonally by secretin andcholecystokinin (CCK). CCKinduces the acinar cells tosecrete the enzymes found in
pancreatic juice. Secretincauses bicarbonate ions toform.
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SMALL INTESTINES
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SMALL INTESTINES
PHYSIOLOCIAL EVENTS
1. Mechanical digestion2. Chemical digestion
3. Absorption
4. Propulsion
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SMALL INTESTINES
MECHANICAL DIGESTION
In segmentation, nonadjacent
segments of the intestinealternately contract andrelax, moving the chymeforward and then backwardresulting through mixing. This
results in the chyme being wellmixed with the enzymes fromthe liver and the pancreas.
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SMALL INTESTINES
In addition, segmentationensures that the chyme wellmove to the plasma
membrane of the lining cells ofthe small intestine. Thesesimple columnar epithelial cellshave brush border enzymeswithin their plasma membrane
which complete the chemicaldigestion of the chyme.
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SMALL INTESTINES
CHEMICAL DIGESTION
Chemical digestion in
the small intestines, is
the result of the
intestinal brush borderenzymes.
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SMALL INTESTINES
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SMALL INTESTINES
SMALL INTESTINES
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SMALL INTESTINES
ABSORPTION
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SMALL INTESTINES
PROTEIN ABSORPTION
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SMALL INTESTINES
LIPID ABSORPTION
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SMALL INTESTINES
LIPID ABSORPTION
SMALL INTESTINES
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SMALL INTESTINES
ABSORPTION
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SMALL INTESTINES
PROPULSION
Propulsion is the result of
peristalsis. This causes
adjacent segments to
alternately contract and
relax.
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SMALL INTESTINES
Peristalsis occurs only
after most nutrients have
been absorbed. It
requires about 2 hours for
undigested material toreach the ileocecal valve.
ILEOCECALVALVE
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
MECHANICAL DIGESTION
Segmentation is initiatedby intrinsic pacemaker cells
in longitudinal smooth
muscle layer.
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
The rate of segmentation in the duodenum
is 12-14 contractions/minute.
Segmentation moves intestinal contents slowly
and steadily toward the ileocecal valve at a rate
which allows time to complete digestion
and absorption. The stomach initiates
the gastroileal reflex, which enhances the force of
segmentation.
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
CHEMICAL DIGESTION
There is no neurological control ofchemical digestion within the small
intestines, this is due to the
natural of the brush border enzymes.
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
ABSORPTION
There is no neurological control ofabsorption within the small
Intestines.
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
PROPULSION
Peristalsis occurs only after most nutrients have been
absorbed. Peristaltic waves initiated in theduodenum begin to sweep slowly along the small
intestines, moving 10-70 cm before dying out. Eachsuccessive wave is initiated a bit more distally, and
this pattern of peristaltic activity, migrating mobility
complex, continues until the undigested food is movedto the ileum a 2 hour trip. The gastroileal reflexcauses the ileocecal sphincter to relax.
SMALL INTESTINES
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SMALL INTESTINES
NEUROLOGICAL CONTROL
Persistalsis is regulated extrinsically
by the autonomic nervoussystem. The parasympathetic
division is excitatory and
the sympathetic is inhibitory.
SMALL INTESTINES
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SMALL INTESTINES
HORMONAL CONTROL
MECHANICAL DIGESTION
Gastrin stimulates
contraction of the
smooth muscle of the
small intestines. This results
in an increase insegmentation.
SMALL INTESTINES
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SMALL INTESTINES
HORMONAL CONTROL
ABSORPTION
ABSORPTION IS INHIBITED BYSOMATOSTATIN.
SMALL INTESTINES
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SMALL INTESTINES
HORMONAL CONTROL
PROPULSION
Perstalsis is stimulated bygastrin. Also, gastrin relaxes
the ileocecal valve,
which allow chyme into
the large intestines.
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LARGE INTESTINES
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LARGE INTESTINES
PHYSIOLOGICAL EVENTS
1. Absorption
2. Propulsion
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LARGE INTESTINES
ABSORPTION
VITAMINS, ELECTROLYTES,AND WATER ARE
ABSORBED IN LARGE
INTESTINES.
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LARGE INTESTINES
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LARGE INTESTINES
Mass movements occurwithin the large intestines.They are long slow-moving
contractile waves that
occur 3 or 4 times per day.Typically mass movements
occur during or aftereating.
LARGE INTESTINES
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NEUROLOGICAL CONTROL
PROPULSION
The presence of food in thestomach activates the
gastroileal reflex in the
small intestines. It, in turn,
stimulates the gastrocolic
reflex of the large intestines.