Digestion,Absorption,And Elimination

8/17/2019 Digestion,Absorption,And Elimination

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Digestion,Absorption,andElimination

Digestion,Absorption,andElimination


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STRUCTURE OF THE DIGESTIVETUBESTRUCTURE OF THE DIGESTIVETUBE

The walls of the digestive tube are made up of fourlayers: themucosa, the submucosa, the muscularis (external muscle layer),and the serosa. The layers are illustrated here.

The walls of the digestive tube are made up of fourlayers: themucosa, the submucosa, the muscularis (external muscle layer),and the serosa. The layers are illustrated here.


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After food enters the mouth, it is pushed down the esophagusthrough a process called peristalsis. The walls of the esophagusconstrict and relax to move the bolus of food toward the stomach.

After food enters the mouth, it is pushed down the esophagusthrough a process called peristalsis. The walls of the esophagusconstrict and relax to move the bolus of food toward the stomach.


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T e Stoma! and SmallIntestineT e Stoma! and SmallIntestine

The bolus of food that enters the stomachcontains some partially digested food andsome food that has not been broken down

at all. n!ymes in the saliva, amylase andlingual lipase, work to digest starch andtriglycerides, respectively.

"igestion of protein and nucleic acids willbegin in the stomach.

The bolus of food that enters the stomachcontains some partially digested food andsome food that has not been broken down

at all. n!ymes in the saliva, amylase andlingual lipase, work to digest starch andtriglycerides, respectively.

"igestion of protein and nucleic acids willbegin in the stomach.


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STO"ACHSTO"ACH

the stomach works to digest proteins in thefood

The connection between the stomach andthe esophagus is called the cardiacsphincter

the stomach works to digest proteins in thefood

The connection between the stomach andthe esophagus is called the cardiacsphincter


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The mucosa of the stomach has severaladaptations not found anywhere else in thedigestive tract. The epithelial cells extend

into the underlying layers of the mucosa toform depressions called gastric pits

These pits are lined with a mixture ofcolumnar epithelial cells and special cellsthat secrete chemicals to aid in digestion

The mucosa of the stomach has severaladaptations not found anywhere else in thedigestive tract. The epithelial cells extend

into the underlying layers of the mucosa toform depressions called gastric pits

These pits are lined with a mixture ofcolumnar epithelial cells and special cellsthat secrete chemicals to aid in digestion


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#oblet cells secrete mucus to protect thestomach lining from other secretions,especially the hydrochloric acid secreted by

another type of cell, the parietal cells.$arietal cells also secrete a chemical calledintrinsic factor that is necessary for theabsorption of vitamin %&' in the smallintestine. f intrinsic factor is not available,the vitamin will not be absorbed and asyndrome called pernicious anemia willresult.

#oblet cells secrete mucus to protect thestomach lining from other secretions,especially the hydrochloric acid secreted by

another type of cell, the parietal cells.$arietal cells also secrete a chemical calledintrinsic factor that is necessary for theabsorption of vitamin %&' in the smallintestine. f intrinsic factor is not available,the vitamin will not be absorbed and asyndrome called pernicious anemia willresult.


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A third type of cell found in the epithelia of thegastric pits is the chief cell. This cell secretes achemical called pepsinogen. hen pepsinogencomes in contact with hydrochloric acid, itchanges into an active en!yme called pepsin.

$epsin begins the digestion of proteins bybreaking large, complex proteins into smaller

pieces that will be further broken apart in thesmall intestine. f hydrochloric acid is notpresent, pepsin will not be formed frompepsinogen and the digestion of protein doesnot begin.

A third type of cell found in the epithelia of thegastric pits is the chief cell. This cell secretes achemical called pepsinogen. hen pepsinogen

comes in contact with hydrochloric acid, itchanges into an active en!yme called pepsin.

$epsin begins the digestion of proteins bybreaking large, complex proteins into smaller

pieces that will be further broken apart in thesmall intestine. f hydrochloric acid is notpresent, pepsin will not be formed frompepsinogen and the digestion of protein doesnot begin.


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The fourth speciali!ed epithelial cell, calledthe # cell, secretes a hormone calledgastrin that is primarily responsible for

stimulating the other three types of cells.*tomach +uids are produced when the #cells are active.

The fourth speciali!ed epithelial cell, calledthe # cell, secretes a hormone calledgastrin that is primarily responsible for

stimulating the other three types of cells.*tomach +uids are produced when the #cells are active.


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REGU#ATI$G DIGESTIO$ I$ THESTO"ACHREGU#ATI$G DIGESTIO$ I$ THESTO"ACH

"igestion in the stomach can be stimulatedin a variety of ways.

– The thought, sight, or smell of food canstimulate the stomach to secrete digestive+uids.

"igestion in the stomach can be stimulatedin a variety of ways.

– The thought, sight, or smell of food canstimulate the stomach to secrete digestive+uids.


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#astric pits, found in the lining of the stomach, contain special cellsthat secrete chemicals used in digestion. *hown here is a

micrograph of gastric pits.

#astric pits, found in the lining of the stomach, contain special cellsthat secrete chemicals used in digestion. *hown here is a

micrograph of gastric pits.


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hen food enters the stomach, it stretchesthe walls of the stomach, resulting inpressure on speciali!ed nerves within the

smooth muscle layers of the stomach. These nerves relay a signal that stimulatesgastrin secretion.

n addition to the action of the stretchreceptors, certain chemicals, such asca eine and alcohol, cause stomach +uidsto be produced. -ighly alkaline food alsocauses stomach secretions to +ow.

hen food enters the stomach, it stretchesthe walls of the stomach, resulting inpressure on speciali!ed nerves within the

smooth muscle layers of the stomach. These nerves relay a signal that stimulatesgastrin secretion.

n addition to the action of the stretchreceptors, certain chemicals, such asca eine and alcohol, cause stomach +uidsto be produced. -ighly alkaline food alsocauses stomach secretions to +ow.


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ncreasing amounts of hydrochloric acid inthe stomach causes the parietal cells todecrease secretion of the acid, slowing

production of pepsin and slowing down theinitial breakdown of proteins.

*tomach digestion is also slowed down bythe actions of the small intestine. hen theacidic stomach contents (called chyme)enter the small intestine, the nervoussystem stimulation of the # cells isinhibited.

ncreasing amounts of hydrochloric acid inthe stomach causes the parietal cells todecrease secretion of the acid, slowing

production of pepsin and slowing down theinitial breakdown of proteins.

*tomach digestion is also slowed down bythe actions of the small intestine. hen theacidic stomach contents (called chyme)enter the small intestine, the nervoussystem stimulation of the # cells isinhibited.


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The presence in the small intestine ofprotein fragments called peptides and fattyacids from triglyceride breakdown also

inhibits the nervous system stimulation ofthe # cells and slows down the mixing ofthe stomach contents.

The presence in the small intestine ofprotein fragments called peptides and fattyacids from triglyceride breakdown also

inhibits the nervous system stimulation ofthe # cells and slows down the mixing ofthe stomach contents.


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S"A## I$TESTI$ES"A## I$TESTI$E

The small intestine has three sections: theduodenum, the e unum, and the ileum.

/hyme from the stomach enters theduodenum portion of the small intestine,which is about &0 inches long. The e unum,or middle segment of the small intestine, isabout 1 feet long. The last portion of thesmall intestine is the ileum, which is about2 feet long. These tubes are bent, folded,and twisted to 3t into the abdominal cavity.

The small intestine has three sections: theduodenum, the e unum, and the ileum.

/hyme from the stomach enters theduodenum portion of the small intestine,which is about &0 inches long. The e unum,or middle segment of the small intestine, isabout 1 feet long. The last portion of thesmall intestine is the ileum, which is about2 feet long. These tubes are bent, folded,and twisted to 3t into the abdominal cavity.


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4illi and microvilli (illustrated here) act to increase the surface area ofthe small intestine, thus increasing the potential for nutrientabsorption. 4illi are 3nger5like pro ections on the surface of theintestine, and microvilli are smaller pro ections stemming from the villi.

4illi and microvilli (illustrated here) act to increase the surface area ofthe small intestine, thus increasing the potential for nutrientabsorption. 4illi are 3nger5like pro ections on the surface of theintestine, and microvilli are smaller pro ections stemming from the villi.


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The duodenum has glands called %runner6sglands in the submucosa. The %runner6sglands secrete an alkaline mucus that helps

to neutrali!e the acidic chyme from thestomach.

The ileum has clumps of lymphoid tissuecalled $eyer6s patches in its submucosa.

This lymphoid tissue helps to screen theingested material in a way similar to whatthe tonsils do

The duodenum has glands called %runner6sglands in the submucosa. The %runner6sglands secrete an alkaline mucus that helps

to neutrali!e the acidic chyme from thestomach.

The ileum has clumps of lymphoid tissuecalled $eyer6s patches in its submucosa.

This lymphoid tissue helps to screen theingested material in a way similar to whatthe tonsils do


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The e unum has no speciali!ed microscopicadaptations in its submucosa.

The e unum has no speciali!ed microscopicadaptations in its submucosa.


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ACCESSOR% ORGA$S& THE #IVER,GA##B#ADDER, A$D 'A$CREAS

ACCESSOR% ORGA$S& THE #IVER,GA##B#ADDER, A$D 'A$CREAS

The liver and the gallbladder are twoimportant accessory digestive organs thatwork with the small intestine. The liver has

several important functions in the body. tregulates carbohydrate, protein, and lipidmetabolism and detoxi3es body wastes anddrugs that have entered the body.

n addition, the liver eliminates bilirubin, awaste product of dead red blood cells, byincorporating it into bile.

The liver and the gallbladder are twoimportant accessory digestive organs thatwork with the small intestine. The liver has

several important functions in the body. tregulates carbohydrate, protein, and lipidmetabolism and detoxi3es body wastes anddrugs that have entered the body.

n addition, the liver eliminates bilirubin, awaste product of dead red blood cells, byincorporating it into bile.


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This +uid, which is stored in the gallbladder,helps digestion by emulsifying fats intosmaller molecules for absorption. %ile is

composed of bile salts, cholesterol, andphospholipids, as well as other substances. The bile salts and lipids work to emulsifyfats. hen needed, bile is released from thegallbladder into the small intestine.

This +uid, which is stored in the gallbladder,helps digestion by emulsifying fats intosmaller molecules for absorption. %ile is

composed of bile salts, cholesterol, andphospholipids, as well as other substances. The bile salts and lipids work to emulsifyfats. hen needed, bile is released from the

gallbladder into the small intestine.


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The pancreas produces hormones, digestiveen!ymes, and bicarbonate to deliver to theduodenum to help digestion.

nsulin and glucagon are two pancreatichormones that work within the body tocontrol blood glucose levels.

The pancreas produces hormones, digestiveen!ymes, and bicarbonate to deliver to theduodenum to help digestion.

nsulin and glucagon are two pancreatichormones that work within the body tocontrol blood glucose levels.


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DIGESTIO$ I$ THE S"A##I$TESTI$EDIGESTIO$ I$ THE S"A##I$TESTI$E

hen acidic chyme enters the duodenum,it triggers several events

The acid, along with short proteins calledpeptides and fatty acids in the chyme,causes cells at the beginning of theduodenum to secrete intestinal +uid.

About & to ' 7uarts of this digestive +uid isproduced each day.

hen acidic chyme enters the duodenum,it triggers several events

The acid, along with short proteins calledpeptides and fatty acids in the chyme,causes cells at the beginning of theduodenum to secrete intestinal +uid.

About & to ' 7uarts of this digestive +uid isproduced each day.


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The intestinal uice, which contains somemucus, is alkaline and helps to neutrali!ethe acidic nature of chyme and protect the

duodenum from the e ects of the acid. The chyme also causes the release of twohormones from the duodenum.

The intestinal uice, which contains somemucus, is alkaline and helps to neutrali!ethe acidic nature of chyme and protect the

duodenum from the e ects of the acid. The chyme also causes the release of twohormones from the duodenum.


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The hormone cholecystokinin (//8) causes thegallbladder to constrict and pump bile into thesmall intestine. //8 also causes the pancreas tosecrete digestive en!ymes into the duodenum.

The hormone secretin causes the pancreas tosecrete large amounts of bicarbonate into thesmall intestine.

The bicarbonate neutrali!es most of thehydrochloric acid from the stomach. After theneutrali!ation occurs, the small intestinecontents are alkaline, creating the conditionsneeded for the digestive en!ymes to work.

The hormone cholecystokinin (//8) causes thegallbladder to constrict and pump bile into thesmall intestine. //8 also causes the pancreas tosecrete digestive en!ymes into the duodenum.

The hormone secretin causes the pancreas tosecrete large amounts of bicarbonate into thesmall intestine.

The bicarbonate neutrali!es most of thehydrochloric acid from the stomach. After theneutrali!ation occurs, the small intestinecontents are alkaline, creating the conditionsneeded for the digestive en!ymes to work.


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The bicarbonate neutrali!es most of thehydrochloric acid from the stomach. Afterthe neutrali!ation occurs, the small

intestine contents are alkaline, creating theconditions needed for the digestiveen!ymes to work.

The bicarbonate neutrali!es most of thehydrochloric acid from the stomach. Afterthe neutrali!ation occurs, the small

intestine contents are alkaline, creating theconditions needed for the digestiveen!ymes to work.


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"igestive en!ymes break starch, proteins, triglycerides,and nucleic acids into intermediate si!e pieces.

$ancreatic amylase breaks down starch. The bicarbonatefrom the pancreas creates the alkaline conditions neededfor amylase and other en!ymes to function. Amylase doesnot break starch into glucose monosaccharide units, butinto smaller pieces, including the disaccharide maltose.

Thus far in the digestive process, the disaccharides, suchas sucrose (from table sugar and fruits) and lactose (frommilk, such as the chocolate shake in our example), thatare ingested have not been broken down.

"ietary triglycerides are broken apart by pancreaticlipase.

"igestive en!ymes break starch, proteins, triglycerides,and nucleic acids into intermediate si!e pieces.

$ancreatic amylase breaks down starch. The bicarbonatefrom the pancreas creates the alkaline conditions neededfor amylase and other en!ymes to function. Amylase doesnot break starch into glucose monosaccharide units, butinto smaller pieces, including the disaccharide maltose.

Thus far in the digestive process, the disaccharides, suchas sucrose (from table sugar and fruits) and lactose (frommilk, such as the chocolate shake in our example), thatare ingested have not been broken down.

"ietary triglycerides are broken apart by pancreaticlipase.


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$roteins are broken into short peptidechains of amino acids by several pancreaticen!ymes, including trypsin, chymotrypsin,

elastase, and carboxypeptidase9ucleic acids are broken into nucleotidesthat will also be further digested at thesurface of the villi.

The 3nal digestion of material occurs at thevilli

$roteins are broken into short peptidechains of amino acids by several pancreaticen!ymes, including trypsin, chymotrypsin,

elastase, and carboxypeptidase9ucleic acids are broken into nucleotidesthat will also be further digested at thesurface of the villi.

The 3nal digestion of material occurs at thevilli


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*peci3c en!ymes are derived from theepithelial cells of the villi that breakdisaccharides, peptides, and nucleotides

into their most basic components forabsorption.

This process works very e ciently becausethe 3nal breakdown of nutrients occurs atthe exact site of nutrient absorption. Thismaterial passes through the lining cellmembranes and into the blood capillaries ofthe villi almost immediately.

*peci3c en!ymes are derived from theepithelial cells of the villi that breakdisaccharides, peptides, and nucleotides

into their most basic components forabsorption.

This process works very e ciently becausethe 3nal breakdown of nutrients occurs atthe exact site of nutrient absorption. Thismaterial passes through the lining cellmembranes and into the blood capillaries ofthe villi almost immediately.


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;ipid absorption is a more complicatedprocess.

#lycerol and short chain fatty acids fromtriglycerides are absorbed by simpledi usion across the cell membranes in thedigestive lining.

/holesterol and long chain fatty acidscannot di use through the cell membranesand must be handled di erently. %ile saltscombine with these fats to form tiny spherescalled micelles

;ipid absorption is a more complicatedprocess.

#lycerol and short chain fatty acids fromtriglycerides are absorbed by simpledi usion across the cell membranes in thedigestive lining.

/holesterol and long chain fatty acidscannot di use through the cell membranesand must be handled di erently. %ile saltscombine with these fats to form tiny spherescalled micelles


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%ecause fats are not water soluble, they cannot easily di use across cellmembranes. Thus, the body has found an alternate way to transport fatdroplets into cells.


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These spheres can pass through the cellmembranes and transport the fats into thecells. %y the time the fats leave the lining

cells, they have been combined with cellproteins that help carry them throughlymph and blood. This combination ofcholesterol, triglycerides, and lining cellproteins is called a chylomicron

These spheres can pass through the cellmembranes and transport the fats into thecells. %y the time the fats leave the lining

cells, they have been combined with cellproteins that help carry them throughlymph and blood. This combination ofcholesterol, triglycerides, and lining cell

proteins is called a chylomicron


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n addition to the nutrients discussed, othermaterials are also absorbed through thesmall intestine, including electrolytes and

trace elements such as sodium,bicarbonate, chloride, iodate, nitrate,calcium, iron, magnesium, and phosphates.

n addition to the nutrients discussed, othermaterials are also absorbed through thesmall intestine, including electrolytes and

trace elements such as sodium,bicarbonate, chloride, iodate, nitrate,calcium, iron, magnesium, and phosphates.


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About = 7uarts of water enter the smallintestine each day.

*ome water is ingested with food (like the

chocolate shake), but most of it enters intothe system at various points during thedigestive process to aid in the breakdown offood.

About = 7uarts of water enter the smallintestine each day.

*ome water is ingested with food (like the

chocolate shake), but most of it enters intothe system at various points during thedigestive process to aid in the breakdown offood.


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The source of these +uids is approximatelyas follows:

– & to ' 7uarts with food, – & 7uart of saliva, – ' 7uarts of stomach (gastric) uices, – & 7uart of bile, ' 7uarts of pancreatic uice, – and & 7uart of intestinal uice.>ost of the water

is reabsorbed through the small intestinal walls.

The source of these +uids is approximatelyas follows:

– & to ' 7uarts with food, – & 7uart of saliva, – ' 7uarts of stomach (gastric) uices, – & 7uart of bile, ' 7uarts of pancreatic uice, – and & 7uart of intestinal uice.>ost of the water

is reabsorbed through the small intestinal walls.


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Any leftover nutrients, waste, and somewater leaves the small intestine and entersthe large intestine.

Absorption of nutrients is complete, butdigestion is not. *ome of the water isabsorbed in the large intestines and verylittle is excreted in the feces.

Any leftover nutrients, waste, and somewater leaves the small intestine and entersthe large intestine.

Absorption of nutrients is complete, butdigestion is not. *ome of the water isabsorbed in the large intestines and verylittle is excreted in the feces.


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T e #arge Intestine andEliminationT e #arge Intestine andElimination

The chyme that enters the large intestine isdi erent from the chyme that enters thesmall intestine.

All of the nutrients that can be absorbedfrom the food have been absorbed, but atype of digestion still occurs in the largeintestine.

The chyme that enters the large intestine isdi erent from the chyme that enters thesmall intestine.

All of the nutrients that can be absorbedfrom the food have been absorbed, but atype of digestion still occurs in the largeintestine.


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;arge numbers of bacteria that live in thelarge intestine 3nish digesting the chymeand use the nutrients for their own

metabolism and growth. These bacteriaalso make vitamins that the body absorbsand uses. 4itamin 8 is one of those vitaminsthat the liver utili!es to make proteins usedin blood clotting

;arge numbers of bacteria that live in thelarge intestine 3nish digesting the chymeand use the nutrients for their own

metabolism and growth. These bacteriaalso make vitamins that the body absorbsand uses. 4itamin 8 is one of those vitaminsthat the liver utili!es to make proteins usedin blood clotting


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This vitamin is so important to us that ifthese bacteria are removed by diarrhea orexcessive antibiotic use, various parts of

the body can bleed for two to three daysafter the bacteria are removed.

The bacteria also make a variety of %vitamins that are used in the metabolism.

This vitamin is so important to us that ifthese bacteria are removed by diarrhea orexcessive antibiotic use, various parts of

the body can bleed for two to three daysafter the bacteria are removed.

The bacteria also make a variety of %vitamins that are used in the metabolism.


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The large intestine consists of the cecum, colon,rectum, and analcanal. t is last place where the body will remove nutrients beforethe waste is excreted.

The large intestine consists of the cecum, colon,rectum, and analcanal. t is last place where the body will remove nutrients beforethe waste is excreted.


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There are four ma or sections of the largeintestine: the cecum, colon, rectum, andanal canal.

t is wider than the previous sections of thedigestive tube and can store material for &'to '? hours until elimination.

The large intestine is connected to thesmall intestine by the ileocecal valve.

There are four ma or sections of the largeintestine: the cecum, colon, rectum, andanal canal.

t is wider than the previous sections of thedigestive tube and can store material for &'to '? hours until elimination.

The large intestine is connected to thesmall intestine by the ileocecal valve.


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The appendix has no function in digestionor absorption, but has several largeaggregates of lymphoid tissue and may

play a role in the immune system. The chemical digestion that occurs in thelarge intestine is carried out by bacteria.

These microorganisms are collectivelycalled @normal +ora because they arenormally found in the colon.

The appendix has no function in digestionor absorption, but has several largeaggregates of lymphoid tissue and may

play a role in the immune system. The chemical digestion that occurs in thelarge intestine is carried out by bacteria.

These microorganisms are collectivelycalled @normal +ora because they arenormally found in the colon.


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. coli, a bacterium that has received a lotof attention, is one of the organisms thatnormally exist in the large intestine.

The intestinal bacteria use whatevercarbohydrates that have not beenseparated and absorbed in the smallintestine.

The bacteria produce waste material thatincludes gases such as hydrogen, nitrogen,methane, carbon hydroxide, and dimethylsul3de.

. coli, a bacterium that has received a lotof attention, is one of the organisms thatnormally exist in the large intestine.

The intestinal bacteria use whatevercarbohydrates that have not beenseparated and absorbed in the smallintestine.

The bacteria produce waste material thatincludes gases such as hydrogen, nitrogen,methane, carbon hydroxide, and dimethyl

sul3de.


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dimethyl sul3de, is responsible for thestrong odor of these gases.

*ome acids will also be produced and, inhigher than normal concentrations, maycause abdominal pain and increase motilityin the large intestine, resulting in diarrhea.

dimethyl sul3de, is responsible for thestrong odor of these gases.

*ome acids will also be produced and, inhigher than normal concentrations, maycause abdominal pain and increase motilityin the large intestine, resulting in diarrhea.


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The bacteria also convert any amino acidsthat enter the large intestine into fattyacids and pass them in the feces.

The bacteria convert bilirubin from the liverto a chemical called stercobilin to producethe normal brown color of feces

f there is no bile coming from the liver orgallbladder, the feces are white or graycolored, and usually high in undigested fatsbecause bile was not present to emulsifydigestive fats

The bacteria also convert any amino acidsthat enter the large intestine into fattyacids and pass them in the feces.

The bacteria convert bilirubin from the liverto a chemical called stercobilin to producethe normal brown color of feces

f there is no bile coming from the liver orgallbladder, the feces are white or graycolored, and usually high in undigested fatsbecause bile was not present to emulsify

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Digestion,Absorption,And Elimination