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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
The Digestive System
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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
Engineers in Physiology
In the 1950s, a chemical engineering professor, Edward Merrill of MIT,was asked to help local doctors measure the viscosity of lung mucus
and human blood (a uids iscosit! is a measure of its thickness, orresistance to ow, when e"posed to stress#$
Edward Merrill
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In 1965, a variety of biocompatible plastics and composites were designed
by chemical engineers for use in prosthetic devicesand replacement valves,
arteries and veins.
The development of the widely used kidney dialysis machine provides a
good example of the lifesaving synergies that can result when biomedical
researchers and chemical engineers wor together.
Adam Heller
!hemical engineer, Adam Heller developed a rapid,
micro-analytical technique re"uiring a much smaller
sample of blood than previous sampling techni"ues#
$ust %&&n', which is about one(eighth of what amos"uito draws when it bites a human being.
)ngineers have built a continuous glucose monitorby
electrically wiring a glucose(reacting protein.
Engineers in Physiology
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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
Engineers in Physiology
Automatic insulin-injection pumps are computeri%eddeice, which draw on well&esta'lished micropumping
techniues deeloped '! chemical and mechanicalengineers, are t!picall! the si%e of a pager and can 'ecarried on a 'elt or shirt pocket$
)ork on microuidic deices has proided fertile groundfor innoatie colla'oration 'etween the chemical
engineering and 'iomedical communities$ Thesee"tremel! small anal!tical deices (often called *lab-on-a-chip+# are used to carr! out arious chemical,'iomedical and thermal reactions, measurements, andanal!ses with greater specicit!, speed, and relia'ilit!than conentional macro&scaled approaches$
-n organ-on-a-chip is a multi&channel .&/ micro uidic cell
culture chip that simulates theactiities, mechanics andph!siological response of entireorgans and organ s!stems$ Theconergence of la's&on&chips andcell 'iolog! has permitted the stud!
of human ph!siolog! in an organ&
specic conte"t, introducing a noel
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Engineering Digestion
ust tr!ing to take a drink or eat a meal in outer space can
'e er! challenging$ 2cientists and engineers who work for3-2- hae designed special deices to help astronauts eat&4Lunch in Outer Space+$
ae !ou heard of *astronaut ice cream or space icecream+6it was designed '! )hirlpool 7orporation undercontract to 3-2- for the -pollo missions$
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On the way to SUPERFOODS..
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The Human
Digestive System
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The Digestive System
Digesi!e ra"# Coninuous $rom mouh o
anus# Consiss o$
%ouh &haryn'
(so)hagus Soma"h Small inesine
# Duodenum# *e+unum# ,leum
Large inesine# Cecum# !!en"i## Colon# e"um
.nus
.""essory digesi!e organs# Sali!ary glands# ('o"rine )an"reas# Biliary sysem
Li!er allbladder
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The Digestive Regimen
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Overview o$ the Digestive System
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The Digestive System
&rimary $un"ion# Trans$er nuriens waer and ele"rolyes $rom
ingesed $ood ino body1s inernal en!ironmen
Four $unctions
# %oiliy
# Se"reion
# Digesion#.bsor)ion
O Di ti S t $ Ch i l
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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
The gus o$ )eo)le $un"ion like in"ustrial chemical
!lants
They are assemblies o$ ubes and anks in whi"h $oods are
hydroly3ed by en3yme-"aaly3ed rea"ions or $ermened by
microorganisms
aw maerials ener a one end wase maer is !oided a
he oher and !aluable )rodu"s are absra"ed on he way
. mill a he enran"e end redu"es he raw maerials osmall $ragmens enabling he rea"ions o )ro"eed $aser
Teeth is li%e a grin"ing mill and he digesi!e ube as a
"hain o$ "hemi"al rea"ors
Our Digestive System !er$orms Chemical
Engineering
E & i h $ E l i l R ' d i $ l $ i ll
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Eco&ot is shor $or Ecological Ro'ot and i re$ers o a "lass o$ energei"ally
auonomous robos ha "an remain sel$-susainable by "olle"ing heir energy $rom
maerial mosly wase maer in he en!ironmen
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Micro-robotic explorers, powered by microbial fuel
cells, could represent an efficient and reliable energy
source on a planet without human intervention
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Digestive Tract
4all has same general sru"ure hroughou lengh$rom eso)hagus o anus
5our ma+or issue layers
# (ucosa
,nnermos layer
# Su'mucosa
# (uscularis e#terna
# Serosa 6uer layer
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)ayers o$ Digestive Tract *all
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(ucosa
Lines luminal sur$a"e o$ digesi!e ra"
Highly $ol"e" sur$ace grealy in"reases absor)i!e area Three layers
# (ucous mem'rane Ser!es as !rotective sur$ace %odi$ied $or se"reion and absor)ion
Conains# E#ocrine glan" cells# se"ree digesi!e +ui"es# En"ocrine glan" cells# se"ree blood-borne gasroinesinal hormones# E!ithelial cells# s)e"iali3ed $or absorbing digesi!e nuriens
# )amina !ro!ria+--loose "onne"i!e issue ouses gu-asso"iaed lym)hoid issue 8,)T9
# ,m)oran in de$ense agains disease-"ausing inesinal ba"eria# (uscularis mucosa
S)arse layer o$ smooh mus"le: it eeps the mucosal surface andunderlying glands in a constant state of gentle agitation to expel contents ofglandular crypts and enhance contact between epithelium and the contents ofthe lumen.
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The Digestive E!ithelium
The oral "a!iy )haryn' and eso)hagus 8where me"hani"al sresses are mos se!ere9
are lined by a strati$ie" s-uamous e!ithelium whereas he soma"h he small
inesine and almos he enire lengh o$ he large inesine 8where absor)ion o""urs9
ha!e a sim!le columnar e!ithelium.
The li$e s)an o$ a y)i"al e)ihelial "ell !aries $rom two to three "ays in he eso)hagus
o u) o si# "ays in the large intestine The lining o$ he enire digesi!e ra" is
"oninuously renewed hrough he di!isions o$ e)ihelial sem "ells kee)ing )a"e wih
he rae o$ "ell desru"ion and loss a e)ihelial sur$a"es
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Su'mucosa
Thi"k layer o$ "onne"i!e issue
&ro!ides digesi!e ra" wih disensibiliy and elasi"iy
Conains larger blood and lym!h!essels
Conains ner!e nework known as su'+mucosal !le#us
(eissners Ple#us/;inner!aes he mu"osal e)ihelial
layer and glands---!ara+sym!athetic stimulation
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(uscularis E#terna
%a+or smooh mus"le "oa o$ digesi!e ube
,n mos areas "onsiss o$ wo layers# Circular layer
,nner layer
Conra"ion de"reases diameer o$ lumen
# )ongitu"inal layer 6uer layer
Conra"ion shorens he ube
Conra"ile a"i!iy )rodu"es )ro)ulsi!e and mi'ing
mo!emens (yenteric0uer'ach1s !le#us
# Lies beween he wo mus"le layers: provides motorinnervations to both layers of the tunica muscularis, havingboth parasympathetic and sympathetic input.
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Serosa
Se"rees serous $lui"
# )u'ricates an" !revents $riction beween
digesi!e organs and surrounding !is"era
Coninuous wih mesenery hroughou mu"h o$ he
ra"
#.a"hmen )ro!ides relai!e $i'aion
# Su))ors digesi!e organs in )ro)er )la"e while
allowing hem $reedom $or mi'ing and )ro)ulsi!e
mo!emens
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Regulation o$ Digestive System
Digesi!e moiliy and se"reion are regulaed by
#.uonomous smooh mus"le $un"ion 8PacesetterCells9: slow wa!e 8B(9
# 2ntrinsicner!e )le'uses
# E#trinsicner!es
# asroinesinal hormones
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Pacesetter cells Ca3al/+generae slow wa!e )oenials he
,1s basi" ele"ri"al rhyhm 8B(9 wa!elike $lu"uaions inmembrane )oenial ransmied hroughou smooh mus"le !ia
ga) +un"ions
Threshold is rea"hed by he e$$e" o$ !arious me"hani"al
neural and hormonal $a"ors in , ra"
These smooh mus"le "ells undergo s)onaneous "onra"ion
ha riggers a wa!e o$ "onra"ion ha s)reads hrough he
enire mus"ular shee &a"eseer "ells are lo"aed in he
muscularis mucosae an" muscularis e#terna he layers o$whi"h surround he lumen o$ he digesi!e ra" The "oordinaed
"onra"ions o$ he mus"ularis e'erna )lay a !ial role in he
mo!emen o$ maerials along he ra" hrough )erisalsis and in
me"hani"al )ro"essing hrough segmenaion
&a"eseer Cells
& i b
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&oins o remember
&a"eseer Cells do no iniiae an a"ion )oenial
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*hy an anti+cholinergic "rug li%e4 anti+
histamines cause consti!ation5
They are also !rescri'e" $or "e!ression 6 slee!
"isor"ers an" gastro intestinal cram!s
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2n ,2 tract Parasym!athetic 7S !lays
ma3or role.Sym!athetic 7S.actsonly un"er e#treme stress
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Rest an" Digest
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Summary o$ Pathways Controlling Digestive
System ctivities
( tilit
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(otility
%oiliy
# %us"ular "onra"ions ha mi' and mo!e $orward
he "onens o$ he digesi!e ra"
# Two y)es o$ digesi!e moiliy
Pro!ulsive movements# &ush "onens $orward hrough he digesi!e ra"
(i#ing movements
# Ser!e wo $un"ions
< %i'ing $ood wih digesi!e +ui"es )romoes digesion o$
$oods
< 5a"iliaes absor)ion by e')osing all )ars o$ inesinal
"onens o absorbing sur$a"es o$ digesi!e ra"
% ili & i l i
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%oiliy--&erisalsis
The )aerns o$ , "onra"ion as a whole "an be
di!ided ino Peristalsis an" Segementation
&erisalsis o""urs as a series o$ !eristaltic wave
cycles in disin" )hases saring wih rela'aion
$ollowed by an in"reasing le!el o$ a"i!iy o a )eak
le!el o$ )erisali" a"i!iy lasing $or =#>= minues
This "y"le re)eas e!ery 8.9:; hours bu is
inerru)ed by $ood ingesion
The role o$ his )ro"ess is likely o clean e#cess
'acteria an" $oo" $rom the "igestive system
&erisalsis o""urs during and shorly a$er a meal
The "onra"ions o""ur in wa!e )aerns ra!eling
down shor lenghs o$ he , ra" $rom one se"ion o
he ne' The contractions occur "irectly 'ehin"
the 'olus o$ $oo" ha is in he sysem $or"ing i
oward he anus ino he ne' rela'ed se"ion o$
smooh mus"le
% ili S i
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%oiliy--Segmenaion
Segmenaion also o""urs during
and shorly a$er a meal wihin shorlenghs in segmened or random
)aerns along he inesine This
!rocess is carrie" out 'y
longitu"inal muscles rela'ing while
"ir"ular mus"les "onra" a
alernaing se"ions hereby mi'ing
he $ood This mi#ing allows $oo"
an" "igestive en
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This is the same %in" o$ muscular
movement that allows worms to move
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&erisalsis and Segmenaion
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&erisalsis and Segmenaion
# iniiaed by !acema%er cells in small inesine
whi"h )rodu"e 'asic electrical rhythm &ER/# Cir"ular smooh mus"le res)onsi!eness is
in$luen"ed by disension o$ inesine gastrin ande'rinsi" ner!e a"i!iy
# 5un"ions %i'ing "hyme wih digesi!e +ui"es se"reed ino small
inesine lumen
(')osing all "hyme o absor)i!e sur$a"es o$ smallinesine mu"osa
%igraing moiliy "om)le'
# Sweeps intestines clean between meals
%oiliy Diseased Condiion
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%oiliy?Diseased Condiion
,n normal digesion $ood "onen is )ro)elled hrough he digesi!e
ra" by rhyhmi" and coor"inate" contractions or !ro!ulsionscalle" !eristalsis
4hen someone su$$ers $rom a digesi!e moiliy disorder )erisalsis
be"omes im)aired resuling in slow "onra"ions ra)id "onra"ions or
ha!ing a "ombinaion o$ boh slow and $as "onra"ions ,n some
"ases )erisalsis may be oally absen
Some )eo)le a$$e"ed by moiliy disorders may be underweigh
Digesi!e moiliy diseases is generally se"ondary when he moiliy)roblem o""urs as a resul o$ a "isease or me"ical con"ition
('am)les o$ se"ondary "auses in"lude "ia'etes4 Par%inson=s
Disease4 en"ocrine "isor"ers4 neurological "isor"ers4 la#ative
a'use4 an" a'"ominal surgery
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(uscles contract in waves to move the $oo" "own the
oeso!hagus. This means that $oo" woul" get to a
!erson=s stomach4 even i$ they were stan"ing on theirhea"
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hat happens if a large chunk of food
gets stuck in esophagus
*hy "oes your stomach Rum'le0,rowl
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*hy "oes your stomach Rum'le0,rowl
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Peo!le who eat on very regular sche"ules may 'e more
susce!ti'le to this RU(&)27,. For e#am!le i$ the
stomach receives $oo" at noon every "ay4 then the 'o"ywill e#!ect $oo" at noon4 whether $oo" is !resent or not.
(a%e sure you eat a HE)TH> 'rea%$ast so that your
'o"y "oesn=t run low on $uel energy/ 'e$ore lunchtime.
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To"ay1s Scenario
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To"ay s Scenario
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2t ta%es your mouth4 eso!hagus4 stomach4small intestine4 large intestine4 gall'la""er4
!ancreas an" liver 3ust to "igest a glass o$
mil%.
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Sali!a
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Sali!a
Saliva* +roduced largely by three ma$or pairs of salivary glands
* !omposition
99.5- /0 &.5- electrolytes and protein amylase, mucus, lyso2yme3
* 4unctions
alivary amylase begins digestion of carbohydrates
4acilitates swallowing by moistening food
ucus provides lubrication and Antibacterial action
alivary ;lands
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alivary glands % pairs3 ( parotid,
sublingual, and submandibular7produce saliva
timulated by thought of food or
ingested food
There is constant low level of
secretion
8asal ate &.5ml:min
The rate depends on "uantity of
food.
alivary ;lands
Control of alivary ecretion
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Control of alivary ecretion
Control o$ Salivary Secretion
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Control o$ Salivary Secretion
Salivary &u$$ering
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Salivary &u$$ering
Sali!a "onains !hos!hate whi"h is "a)able o$ bu$$ering he
)
Phos!hate is a goo" 'u$$er an" !hos!hate salts are widely
used in s"ien"e o )re)are bu$$er soluion owe!er alhough we
hink o$ sali!a as "onaining a lo o$ )hos)hae i +us does no
"onain enough o allow i o be really e$$e"i!e in vivo.
This lea!es us wih bi"arbonae whi"h is o$en re$erred o as he
ma+or bu$$er o$ sali!a ,n mouh bi"arbonae a"s mainly o
neurali3e a"id
The normal4 resting4 !H o$ the mouth "oes not $all much
'elow a'out !H ?.@ an" the reason $or this is the
'icar'onate.
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Cha)er >@ The Digesi!e Sysem
Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
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Cha)er >@ The Digesi!e Sysem
Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
Stomach
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Stomach
Three main $un"ions# Store ingeste" $oo" unil i "an be em)ied ino small inesine# Se"rees hy"rochloric aci" HCl/ and en
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Has $oo" "igestion starte" 'e$ore
reaching stomach5
Heart'urn
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Heart'urn
,astric (otility
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,astric (otility
5our as)e"s
# 5illing ,n!ol!es Rece!tive Rela#ation
# (nhan"es soma"h1s abiliy o a""ommodae he e'ra!olume o$ $ood wih lile rise in soma"h )ressure
# Triggered by a" o$ eaing
# %ediaed by Aagus nerve
# Sorage Ta%es !lace in 'o"y0$un"us o$ stomach 555
%i'ing
Takes )la"e in anrum o$ soma"h# Em!tying
)argely controlle" 'y $actors in "uo"enum
,astric Em!tying an" (i#ing as a Result o$
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ntral Peristaltic Contractions
,astric Em!tying
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,astric Em!tying
5a"ors in soma"h# mount o$ chyme in stomach is main $actor that in$luences
strength o$ contraction
5a"ors in duodenum# Fat
5a digesion and absor)ion akes )la"e only wihin lumen o$ smallinesine
*hen $at is alrea"y in "uo"enum $urher gastric em!tying o$addiional $ay soma"h "onens is !revente"
# ci" Un+neutrali
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,ast c !ty g
5a"ors rigger eiher
# 7eural res!onse %ediaed hrough boh inrinsi" ner!e )le'uses 8shor re$le'9
and auonomi" ner!es 8long re$le'9
Colle"i!ely "alled enterogastric re$le#
.ddiional $a"ors ha in$luen"e gasri" moiliy
# Emotions
Sa"ness an" $ear# end o de"rease moiliy nger an" aggression# end o in"rease moiliy
# 2ntense !ain# ends o inhibi moiliy
,astric Secretions
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Two disin" areas o$ gasri" mu"osa ha se"ree gasri" +ui"e
#O#yntic mucosa Lines body and $undus
# Pyloric glan" area P,/
Lines he anrum
asri" glands a base o$ gasri" )is-
Three y)es o$ gasri" e'o"rine se"reory "ells# (ucous cells
Line gasri" )is and enran"e o$ glands
Se"ree hin waery mu"us
# Chie$ cells
Se"ree en3yme )re"ursor Pe!sinogen 555/
# Parietal o#yntic/ cells
Se"rees HCl5555
Colle"i!ely hey make ,astric Buice
HCl an" its Role
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Functions o$ HCl#."i!aes !e!sinogen to active en
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Hormonal Regulation
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Aagussimulaion and ctsimulaes
)arieal and "hie$ "ells
"ells are simulaed by !agalsimulaion hrough gastrin+releasing
!e!ti"e his "auses he "ells o
se"ree gasrin whi"h in urn no only
dire"ly simulaes )arieal "ells bu
hrough EC) cells o release
histamine
These "ells are simulaed by he
hormone gastrin
isamine and gasrin a"
synergisi"ally as he mos im)oran
simulaors o$ CL se"reion $rom
)arieal "ells and simulaors o$
se"reion o$ !e!sinogen $rom chie$
cells.
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The stomach is exposed to the harshest conditions in the digestive tract
!o keep from digesting itself, the stomach has a mucosal barrierwiths ma$or biochemical factory
Importance to digestive system * secretion of bile salts
)iver
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&ile# ."i!ely se"reed by li!er and a"i!ely di!ered o gallbladder beween meals# Sored and "on"enraed in gallbladder# Consiss o$
&ile salts Cholesterol Le"ihin Bilirubin
# .$er meal bile eners duodenum
&ile salts# Deri!ai!es o$ "holeserol# Con!er large $a globules ino a liuid emulsion# .$er )ari"i)aion in $a digesion and absor)ion mos are reabsorbed ino he blood
Pancreatic )i!ases
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Digestion an" 'sor!tion o$ Fats
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*ho are the $erries in your $at
"igestion555
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*here are the chylomicrons $orme"
insi"e the cells5
*hy cant they enter the 'loo" vessels5
*hy "o we $eel slee!y a$ter eating
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How "oes the 'o"y a'sor' vitamins5
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The small intestine is where vitamin absorption happens along with most other
types of absorption3. ?ater(soluble vitamins, such as vitamin !, have @activetransports@ for absorption (( molecules that pic them up in the small intestine,
in a section called the#e#unum&
The 8 vitamins are also water(soluble and need to be replenished every day,
although their absorption wors a bit differently. TheyAre bound to proteins andtherefore re"uire a protein breadown triggered by stomach acids. =bsorption of
most of the 8 vitamins happens further down in the small intestine, in the ileum.
!he other type of vitamin, the fat-soluble ones such as A, %, " and (, need
to dissolve in fat before they can make it into the body. The process re"uiresfat(digesting bile acids that come from the liver and live in the small intestine.
?hen the bile acids brea down the fat the vitamins are dissolved in, the
vitamins move with the fat through the intestinal wall, into the body, and finally
end up in the liver and in body fat, where theyAre stored until theyAre needed
much lie fat3.
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Try!sin "lea!es )e)ide bonds on he "arbo'yl side o$ basi" amino a"ids 8lysine and arginine9
Chymotry!sin "lea!es )e)ide bonds on he "arbo'yl side o$ aromai" amino a"ids 8ryosine)henylalanine and ry)o)han9
Car'o#y!e!ti"ases 3in"-"onaining meallo-en3ymes ha remo!e single amino a"ids $rom
he "arbo'yl-erminal ends o$ )roeins and )e)ides
Small 2ntestine
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Cha)er >@ The Digesi!e SysemHuman Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
Sie where mos digesion and absor)ion 8E=F9
ake )la"e Three segmens
# Duodenum
# *e+unum
# ,leum
%oiliy in"ludes
# Segmenaion
# %igraing moiliy "om)le'
Large ,nesine
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&rimarily a drying and sorage organ
Consiss o$# Colon
# Cecum
# !!en"i#
# Rectum Conens re"ei!ed $rom small inesine "onsiss o$
indigesible $ood residues unabsorbed biliary"om)onens and remaining $luid
Colon# E#tracts more water an" salt $rom contents
# 5e"es # wha remains o be eliminaed
Large ,nesine
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Cha)er >@ The Digesi!e SysemHuman Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning
Large ,nesine
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(ass movements
# %assi!e "onra"ions# %o!es "oloni" "onens ino disal )ar o$ large inesine ,astrocolic re$le#
# %ediaed $rom soma"h o "olon by gasrin and byauonomi" ner!es
# %os e!iden a$er $irs meal o$ he day# 6$en $ollowed by urge o de$e"ae De$ecation re$le#
# ,niiaed when sre"h re"e)ors in re"al wall are simulaedby disension
# Causes inernal anal s)hin"er o rela' and re"um andsigmoid "olon o "onra" more !igorously# ,$ e'ernal anal s)hin"er 8skeleal mus"le under !olunary
"onrol9 is also rela'ed de$e"aion o""urs