digestion physiology a&p ii

8/8/2019 Digestion Physiology a&p II

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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



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


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



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


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


1. Mechanical digestion


3. Propulsion

4. Absorption


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STOMACH


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



1. Pace-maker cells--interstitial cells of Cajal

establish intrinsic control.2. Vagus nervecontrol mechanical digestionextrinsically.


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STOMACH


CHEMICALDIGESTION


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STOMACH


CEPHALIC PHASE

Slight, thought, taste, orsmell of food causesstimulation of the vagus.The vagus stimulates theproduction of gastricjuice.


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STOMACH


GASTRIC PHASE

Stomach distention willact locally or evoke thevagovagal reflex.

VAGOVAGAL

REFLEX


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STOMACH


CHEMICAL DIGESTION

Intestinal phase


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STOMACH


PROPULSION

1. Pace-maker cells--interstitial cells of Cajal

establish intrinsic control.2. Vagus nervecontrol mechanical digestionextrinsically.


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STOMACH


ABSORPTION

1. NONE


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STOMACH

HORMONAL CONTROL


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


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



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LIVER GALLBLADDER


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




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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


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


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



Segmentation is initiatedby intrinsic pacemaker cells

in longitudinal smooth

muscle layer.

SMALL INTESTINES


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SMALL INTESTINES


SMALL INTESTINES


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SMALL INTESTINES


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


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


ABSORPTION

There is no neurological control ofabsorption within the small

Intestines.

SMALL INTESTINES


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SMALL INTESTINES


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


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


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


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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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.

digestion physiology a&p ii

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