Anatomy & Physiology of GIT

Anatomy & Physiology of GIT: It covers Organs of the Digestive system, Structure of the Alimentary canal, Mouth, Salivary glands, Pharynx, Oesophagus, Stomach, Small intestine, Large intestine, Rectum & Anal canal, Pancreas, Liver, Biliary tract

1. ANATOMY & PHYSIOLOGY
OF GIT

2. CONTENTS
➢Organs of the Digestive
system
➢Structure of the
Alimentary canal
➢Mouth
➢Salivary glands
➢Pharynx
➢Oesophagus
➢Stomach
➢Small intestine
➢Large intestine, Rectum
& Anal canal
➢Pancreas
➢Liver
➢Biliary tract

4. ORGANS OF THE DIGESTIVE SYSTEM
A.Alimentarycanal
-ItisalsoknownastheGI(Gastrointestinal)tract.
-ThelengthoftheGItractisabout5–7metersinalivingperson.
-Itislongerinacadaver(about7–9meters)becauseofthelossofmuscletoneafterdeath.
Parts:-
5. Small intestine
6. Large intestine
7. Rectum and anal canal
1. Mouth
2. Pharynx
3. Esophagus
4. Stomach

5. B.Accessoryorgans
-Thesearethegroupoforgansthatarepresentinthealimentarycanalwhicheither
secreteorstorethegastriccontentsandaidindigestionprocess.
-Theseinclude:-
1.Teeth
2.Tongue
3.Salivaryglands
4.Liver
5.Gallbladderpancreas
-TheglandspresentthroughouttheGItractpourouttheirsecretionsintothesystemto
facilitatedigestion.
Ex.Gastricjuicesecretedbyglandsintheliningofthestomach,etc.

6. STRUCTURE OF THE ALIMENTARY CANAL
Thewallsofthealimentarytractareformedof4layersoftissue:
Layers of the
GIT
Mucosa
(Innermost
lining)
SubmucosaMuscularis
Serosa
(outermost
covering)

7. SEROSA
Inthorax,itconsistsofloosefibroustissueandintheabdomentheorgansarecovered
byserousmembranecalled–Peritoneum.
PERITONEUM
Itisthelargestserousmembraneofthebody.
Provideslocalbarriertospreadofinfections.
Hastwolayers:
Parietal peritoneum
-lines adnominal wall
Visceral peritoneum
•covers the organs within abdomen

8. MUSCULARIS
Itconsistsoftwolayersofsmoothmuscle.
Betweenthe2layersarebloodandlymphvessels,andanetworkofSympatheticand
Parasympatheticnerves–Myentericplexus.
ContractionandrelaxationofthemuscularlayercalledPeristalsisareunderthe
influenceofsympatheticandparasympatheticnerves.
Sphincters–thickenedringsofcircularmuscle;regulateforwardmovementofthe
foodmaterials
Smooth Muscle
of Muscularis
Longitudinal
Outer layer
Circular
Inner layer

9. SUBMUCOSA
Consistsoflooseareolarconnective
tissuecontainingCollagenandElastin
fibres.
Itcontainsbloodvessels,lymphvessels,
nervesandvaryingamountsoflymphoid
tissues.
Thelayeralsocontainsaneuralnetwork
–Submucosalplexus,whichcontains
sympatheticandparasympatheticnerves
thatsupplythemucosallining.

10. MUCOSA
Consists of three layers:-
1.Mucus membrane –innermost –columnar
epithelium; func. –protection, secretion,
absorption.
2.Lamina propria –middle layer –loose
connective tissue; func. –supports blood vessels
that nourish inner epithelial layer.
3.Muscularis mucosa –outermost –thin layer of
smooth muscle; func. –forms gastric glands, etc.

11. Mucus Membrane:
-Predominantly made of stratifies
squamous epithelium with mucus
secreting glands just below the
surface.
-In areas where secretion of digestive
juices and absorption occur, the
membrane consists of columnar
epithelial cells with scattered mucus
secreting Goblet cells.

12. Intheregionslinedwithcolumnarepithelialcellsarecollectionsofspecialisedcellsorglands,which
releasetheirsecretionsintothelumenofthetract.
Theseinclude:
Saliva from salivary glands
Gastric juice from gastric glands
Pancreatic juice from pancreas
Intestinal juice from intestinal glands
Bile from liver

13. ENTERIC NERVOUS
SYSTEM
Myenteric plexus -located between the
longitudinal and circular smooth muscle layers
of the muscularis.
Submucosal plexus -found within the
submucosa.
ENS consist of motor neurons, interneurons,
and sensory neurons.
Motor neurons -supply the longitudinal and
circular smooth muscle layers of the muscularis
-controls GI tract motility.
Motor neurons -supply the secretory cells of
the mucosal epithelium -controls the secretions
of the organs of the GI tract.

14. ENTERIC NERVOUS SYSTEM
Interneurons of the ENS -interconnect the neurons
of the myenteric and submucosal plexuses.
The sensory neurons of the ENS supply the mucosal
epithelium.
The wall of the GI tract contains two major types
of sensory receptors:
(1) chemoreceptors -which respond to certain
chemicals in the food present in the lumen.
(2) mechanoreceptors (such as stretch receptors) -
are activated when food stretches the wall of a GI
organ.

15. AUTONOMIC
NERVOUS
SYSTEM
Parasympathetic Control:-
The Vagus (X) nerves supply parasympathetic
fibers to most parts of the GI tract –except the
last half of the large intestine, which is supplied
with parasympathetic fibers from the sacral
spinal cord.
Parasympathetic nerves of the GI tract –form
neural connections with the ENS.
In general, stimulation of the parasympathetic
nerves –increase in GI secretion and motility.

16. Sympathetic
Control:-
Sympathetic
nerves that
supply the GI
tract arise from
the thoracic and
upper lumbar
regions of the
spinal cord
In general, the
sympathetic
nerves –
decrease in GI
secretion and
motility.
Emotions such as
anger, fear, and
anxiety may
slow digestion
because they
stimulate the
sympathetic
nerves that
supply the GI
tract.

18. DESCRIPTION OF THE
ORGANS OF GIT

19. MOUTH
Themouthororalcavityisboundedbymusclesandbones:
-Anteriorly–bythelips
-Posteriorly–itiscontinuouswiththeoropharynx
-Laterally–bythemusclesofthecheeks
-Superiorly–bythebonyhardpalateandmuscularsoftpalate
-Inferiorly–bythemusculartongueandthesofttissuesofthefloorofthemouth.
Linedthroughoutwithmucousmembrane,consistingofstratifiedsquamousepitheliumcontainingsmallmucus-
secretingglands.
Thepalate–dividedintotheanteriorhardpalateandtheposteriorsoftpalate.
TheUvula–acurvedfoldofmusclecoveredwithmucousmembrane,hanging
downfromthemiddleofthefreeborderofthesoftpalate.
Palatinetonsilsarepresentintheoralcavitybetweenthefoldsofthemucus
membranes.

20. Tongue
Thetongueiscomposedofskeletalmusclecoveredwith
mucousmembrane.
Composedofvoluntarymuscles.
Itisattachedbyitsbasetothehyoidboneandbyafoldof
itsmucousmembranecovering,calledthefrenulum,tothe
floorofthemouth.
Thesuperiorsurfaceconsistsofstratifiedsquamous
epithelium,withnumerouspapillae(smallprojections).
Manyofthepapillaecontainsensoryreceptorsforthesense
oftasteinthetastebuds.
Lingualglandsinthelaminapropriaofthetonguesecrete
bothmucusandawateryserousfluidthatcontainsthe
enzymelinguallipase.

21. NervesupplytoTongue
Thenervesinvolvedare:
1.thehypoglossalnerves–supplythevoluntarymuscle.
2.thelingualbranchofthemandibularnerves–arisefromthe5thcranialnerves–somatic
sensation,i.e.pain,temperatureandtouch.
3.thefacialandglossopharyngealnerves–thenervesoftaste.
Functionsofthetongue
Thetongueplaysanimportantpartin:
1.Chewingthecontentsinthemouth
2.Swallowingthecontentsinthemouth
3.Speech
4.Taste
Nerveendingsofthesenseoftaste–presentinthepapillae–widelydistributedinthe
epitheliumofthetongue.

22. TEETH
Humanbabiesarebornwith2setsofteeth(dentition):
•Theteeth-accessorydigestiveorganslocatedinsocketsofthealveolarprocessesofthe
mandibleandmaxillae.
Dentition
Deciduous or
Temporary Teeth
(20 in number)
Permanent Teeth
(32 in number)

23. Atypicaltoothhasthreemajorregions:
1.thecrown–thepartthatprotrudesfromthegum
2.theroot–thepartembeddedinthebone
3.theneck–theslightlynarrowedregionwherethecrownmergeswiththeroot.
Inthecentreofthetoothisthepulpcavitycontainingbloodvessels,lymphvesselsand
nerves–surroundedbyahardsubstancecalleddentine(hashighcontentof
hydroxyapatite).
•Thedentineofthecrowniscoveredbyathinlayerofveryhardsubstance,enamel(hardestsubstanceinthebody)–consistsprimarily
ofcalciumphosphateandcalciumcarbonate.
•Therootofthetooth,ontheotherhand,iscoveredwithasubstanceresemblingbone,calledcementum,whichsecuresthetoothinits
socket.
•Bloodvesselsandnervespasstothetooththroughasmallholeattheapexofeachroot.

24. Functionsoftheteeth
Teethhavedifferentshapesdependingontheirfunctions.
Theyhelpinmechanicaldigestionofthefoodinthemouthandhelpmixingthecontentswith
saliva.
-cutting teeth, used for biting off pieces of
food.
Incisors and Canine teeth
-used for grinding or chewing food
Premolar and Molar teeth

25. SALIVARY GLANDS
Asalivaryglandisaglandthatreleasesasecretioncalledsalivaintotheoralcavity.
Whenfoodentersthemouth,however,secretionofsalivaincreases,anditlubricates,dissolves,
andbeginsthechemicalbreakdownofthefood.
TherearethreepairsofSalivaryglands:
1.Parotidglands–situatedoneoneachsideofthefacejustbelowtheexternalacoustic
meatus-eachglandhasaparotidductopeningintothemouthatthelevelofthesecond
uppermolartooth.
2.Submandibularglands–lieoneoneachsideofthefaceundertheangleofthejaw-
submandibularductsopenonthefloorofthemouth,oneoneachsideofthefrenulumofthe
tongue.
3.Sublingualglands–lieunderthemucousmembraneofthefloorofthemouthinfrontof
thesubmandibularglands.

26. StructureofSalivaryGlands
Theglandsareallsurroundedbyafibrouscapsule.
Theyconsistofanumberoflobulesmadeupofsmallacinilinedwithsecretorycells.
Secretionsarepouredintoductulesthatjoinuptoformlargerductsleadingintothe
mouth.
Compositionofsaliva
Salivaisthecombinedsecretionsfromthesalivaryglandsandthesmallmucous-secreting
glandsoftheoralmucosa.
About1.5litersofsalivaisproduceddailyanditconsistsof:
Lysozyme Water Mucus
Mineral salts
Salivary
amylase
Immunoglobulin
s

27. FunctionsofSaliva
1.Chemicaldigestionofpolysaccharides
2.Lubricationoffood
3.Cleaningandlubricatingthemouth
4.Non-specificdefense–Lysozymeandimmunoglobulinspresentinsalivacombat
invadingmicrobes.
5.Taste-tastebudsarestimulatedonlybychemicalsubstancesinsolutionand
thereforedryfoodsonlystimulatethesenseoftasteafterthoroughmixingwith
saliva.

28. PHARYNX
Whenfoodisfirstswallowed,itpassesfromthemouthintothepharynx,afunnel-shapedtube
thatextendsfromtheinternalnarestotheesophagusposteriorlyandtothelarynxanteriorly.
Thepharynxisdividedfordescriptivepurposeintothreeparts,thenasopharynx,oropharynx
andlaryngopharynx.
Nasopharynx
-respiration.
Oropharynx and Laryngopharynx
-common to both the respiratory and the digestive systems.

29. The walls of the pharynx consist of three
layers of tissue:
-The lining membrane (mucosa) is stratified
squamous epithelium, continuous with the
lining of the mouth at one end and the
esophagus at the other.
-The middle layer consists of connective
tissue, which becomes thinner towards the
lower end and contains blood and lymph
vessels and nerves.
-The outer layer consists of a number of
involuntary muscles that are involved in
swallowing.

30. ESOPHAGUS
Theesophagusisabout25cmlongandabout2cmindiameterandliesinthe
medianplaneinthethoraxinfrontofthevertebralcolumnbehindthetrachea
andtheheart.
Itiscontinuouswiththepharynxaboveandjustbelowthediaphragmitjoinsthe
stomach.
Ateachendoftheesophagus,themuscularisbecomesslightlymoreprominent
andformstwosphincters:
1.TheUpperEsophagealSphincter(UES)-skeletalmuscle(preventsair
passingintotheesophagusduringinspirationandtheaspirationof
esophagealcontents).
2.TheLowerEsophageal(cardiac)Sphincter(LES)-smoothmuscleandisnear
theheart(preventstherefluxofacidgastriccontentsintotheesophagus).
Theesophagussecretesmucusandtransportsfoodintothestomach.
Itdoesnotproducedigestiveenzymes,anditdoesnotcarryonabsorption

31. Structure of Esophagus
There are all the 4 layers of tissues i.e.Serosa, Muscularis,
Submucosa & Mucosa.
As the esophagus is almost entirely in the thorax the
outer covering –the adventitia, consists of elastic fibrous
tissue that attaches the esophagus to the surrounding
structures.
The proximal third is lined by stratified squamous
epithelium, the distal third by columnar epithelium and
the middle third is lined by a mixture of the two.
Functions of the mouth, pharynx and esophagus
1. Formation of a bolus.
-When food is taken into the mouth it is chewed by the
teeth and moved around the mouth by the tongue and
muscles of the cheeks.
-It is mixed with saliva and formed into a soft mass or
bolusready for swallowing.

32. 2.Swallowing(deglutition).
-Thebolushasbeenformed.Itisinitiatedvoluntarilybutcompleted
byareflex(involuntary)action.
1.Oralstage–Withthemouthclosed,thevoluntarymusclesofthe
tongueandcheekspushthebolusbackwardsintothepharynx.
2.Pharyngealstage.Themusclesofthepharynxarestimulatedbya
reflexactioninitiatedinthewallsoftheoropharynxandcoordinated
bytheswallowingcentreinthemedulla.Involuntarycontractionof
thesemusclespropelsthebolusdownintotheesophagus.
3.Esophagealstage.Thepresenceofthebolusinthepharynx
stimulatesawaveofperistalsisthatpropelsthebolusthroughthe
esophagustothestomach.

33. STOMACH
ThestomachisaJ-shapedorganoftheGItractdirectlyinferiortothediaphragminthe
abdomen.
Itissituatedintheepigastric,umbilicalandlefthypochondriacregionsoftheabdominalcavity.
Thestomachconnectstheesophagustotheduodenum.
StructureofEsophagus
Thestomachhasfourmainregions:
-thecardia,fundus,body,andpyloricpart.

34. Cardia –surrounds the opening of the esophagus
into the stomach.
Fundus–rounded portion superior to and to the left
of the cardia.
Body–Inferior to the fundus, it is the large central
portion of the stomach.
Pyloricpart is divisible into three regions.
1.Pyloric antrum -connects to the body of the
stomach.
2.Pyloric canal -leads to the third region, the
pylorus.
3.Pylorus -connects to the duodenum.
The pylorus communicates with the duodenum of the
small intestine via a smooth muscle sphincter called
the pyloric sphincter.

35. Wallsofthestomach
-Thefourlayersoftissuethatcomprisethebasicstructureofthealimentarycanalare
foundinthestomachbutwithsomemodifications.
Musclelayer
-Thisconsistsofthreelayersofsmoothmusclefibres:
Mucosa
-Numerousgastricglandsaresituatedbelowthesurfaceinthemucousmembraneand
openontoit.
-Theyconsistofspecializedcellsthatsecretegastricjuiceintothestomach
-an outer layer of longitudinal fibers
-a middle layer of circular fibers.
-an inner layer of oblique fibers.

36. GastricJuiceandFunctionsofStomach
Gastricjuice
Itconsistsof:
1.Water
2.Mineralsalts
3.MucussecretedbyMucousneckcellsintheglandand
surfacemucouscellsonthestomachsurface
4.Hydrochloricacid
5.Intrinsicfactor
6.Inactiveenzymeprecursors:PepsinogenssecretedbyChief
cellsintheglands.
secreted by Parietal cells
in the gastric glands

37. FunctionsofGastricJuice
1.Waterfurtherliquefiesthefoodswallowed.
2.Hydrochloricacid:–acidifiesthefoodandstopstheactionofsalivaryamylase
–killsingestedmicrobes
–providestheacidenvironmentneededfortheactionofpepsins.
3.Pepsinogensareactivatedtopepsinsbyhydrochloricacidandbypepsinsalreadypresent
inthestomach.ActiveinpHrangeof1.5to3.5.
4.Intrinsicfactor(aprotein)isnecessaryfortheabsorptionofvitaminB12fromtheileum.
(Deficiencyleadstoperniciousanemia)
5.Mucuspreventsmechanicalinjurytothestomachwallbylubricatingthecontents.Italso
preventschemicalinjurybyactingasabarrierbetweenthestomachwallandthecorrosive
gastricjuice.

38. Secretion of HCl by parietal cells in the
stomach
Regulation of HCl secretion
➢HCl secretion by parietal cells can be stimulated by
several sources: acetylcholine (ACh), gastrin, and histamine
➢Proton pumps, powered by ATP, secrete the H
+
Cl
-
diffuses into the stomach lumen through Cl channels.

39. Functions of Stomach
1.Temporary storage allowing time for the digestive
enzymes, pepsins, to act.
2.Chemical digestion –pepsins break proteins into
polypeptides.
3.Mechanical breakdown –the three smooth muscle
layers enable the stomach to act as a churn, gastric
juice is addedand the contents are liquefied to
chyme.
4.Limited absorption –water, alcohol and some lipid
soluble drugs.

40. Functions of Stomach
1.Non-specific defense against microbes –
provided by hydrochloric acid in gastric juice.
2.Preparation of iron for absorption.
3.Production and secretion of intrinsic factor.
4.Secretion of the hormone Gastrin, secreted by
the G cells (stimulates gastric glands to produce
more gastric juice).
Cont

41. SMALL INTESTINE
Thesmallintestineiscontinuouswiththestomachatthepyloricsphincter.
Thesmallintestineisabout2.5cmindiameter,alittleover5meterslongandleads
intothelargeintestineattheileocaecalvalve.
Inthesmallintestinethechemicaldigestionoffoodiscompletedandabsorptionof
mostnutrientstakesplace.
Itconsistsofthreeparts:
1.Duodenum–Secretionsfromthegallbladderandpancreasmergeinacommon
structure–thehepatopancreaticampulla–andentertheduodenumatthe
duodenalpapilla.Theduodenalpapillaisguardedbyaringofsmoothmuscle,the
hepatopancreaticsphincter(ofOddi).
2.Jejunum–themiddlesectionofthesmallintestine.
3.Ileum–terminalsection-endsattheileocaecalvalve,whichcontrolstheflowof
materialfromtheileumtothecaecum.

42. StructureofSmallIntestine
A.Peritoneum
Themesentery–doublelayerofperitoneum,attachesthejejunumandileum
totheposteriorabdominalwall.
B.Mucosa
Thesurfaceareaofthesmallintestinemucosaisgreatlyincreasedby
permanentcircularfolds,villiandmicrovilli.
Thepermanentcircularfolds,unliketherugaeofthestomach,arenot
smoothedoutwhenthesmallintestineisdistended.Theypromotemixingof
chymeasitpassesalong.
Thevilliaretinyfinger-likeprojectionsofthemucosallayerintotheintestinal
lumen,about0.5–1mmlong.
Theircoveringconsistsofcolumnarepithelialcells(enterocytes)withtiny
microvilli(1μmlong)ontheirfreeborder.
Gobletcellsthatsecretemucusareinterspersedbetweentheenterocytes.
Lymphcapillariesarecalledlactealsbecauseabsorbedfatgivesthelympha
milkyappearance.

43. Theintestinalglandsaresimpletubularglandssituated
belowthesurface,betweenthevilli.
Numerouslymphnodesarefoundinthemucosaat
irregularintervalsthroughoutthelengthofthesmall
intestine.
Thesmalleronesareknownassolitarylymphatic
follicles,andcollectionsofabout20or30largernodes
situatedtowardsthedistalendoftheileumarecalled
aggregatedlymphaticfollicles(Peyer’spatches).
Theselymphatictissues,packedwithdefensivecells,are
strategicallylocatedtoneutralizeingestedantigens.

44. IntestinalJuice
About1500mLofintestinaljuicearesecreteddailybytheglandsofthesmallintestine.
Itisslightlyalkalineandconsistsofwater,mucusandmineralsalts.
FunctionsofSmallIntestine
1.Onwardmovementofitscontentsbyperistalsis,whichisincreasedbyparasympathetic
stimulation.
2.Secretionofintestinaljuice,alsoincreasedbyparasympatheticstimulation.
3.Completionofchemicaldigestionofcarbohydrates,proteinandfatsintheenterocytesof
thevilli.
4.Protectionagainstinfectionbymicrobesthathavesurvivedtheantimicrobialactionofthe
hydrochloricacidinthestomach.
5.SecretionofthehormonesCholecystokinin(CCK)andSecretin.
6.Absorptionofnutrients.

45. Absorption of digested nutrients in the small intestine
(a) Mechanisms for movement of nutrients through
absorptive epithelial cells of villi
(b) Movement of absorbed nutrients into blood and lymph

46. LARGE INTESTINE, RECTUM & ANAL CANAL
ThelargeintestineistheterminalportionoftheGItract.
Theoverallfunctionsofthelargeintestinearethecompletionofabsorption,theproductionof
certainvitamins,theformationoffeces,andtheexpulsionoffecesfromthebody.
Thelargeintestineextendsfromtheileumtotheanus.
Itisattachedtotheposteriorabdominalwallbyitsmesocolon,whichisadoublelayerof
peritoneum.
Structurally,thefourmajorregionsofthelargeintestineare:
Large
Intestine
Cecum Colon Rectum
Anal
canal

47. Thecaecum
-Thisisthefirstpartofthelargeintestine.
-Itisthejunctionwhenthesmallintestineandlargeintestinemeet.
-Justbelowthejunctionofthetwo,theileocaecalvalveopensfromtheileum.
-Thevermiformappendixisafineworm-liketube,closedatoneend,whichleadsfrom
thecaecum,containslymphoidtissue.
Thecolon
-Thecolonhasfourpartswithsamestructureandfunctions:
1.Theascendingcolon–Thispassesupwardsfromthecaecumtothelevelofthe
liverwhereitcurvestotheleftatthehepaticflexuretobecomethetransverse
colon.
2.Thetransversecolon–Thispartextendsacrosstheabdominalcavityinfrontofthe
duodenumandthestomachtotheareaofthespleenwhereitformsthesplenic
flexureandcurvesacutelydownwardstobecomethedescendingcolon.

48. 3.Thedescendingcolon–Thispassesdowntheleft
sideoftheabdominalcavitythencurvestowardsthe
midline.Attheleveloftheiliaccrestitisknownas
thesigmoidcolon.
4.Thesigmoidcolon–ThispartdescribesanS-
shapedcurveinthepelviccavitythatcontinues
downwardstobecometherectum.
Therectum
-Thisisaslightlydilatedsectionofthelargeintestine.It
leadsfromthesigmoidcolonandterminatesintheanal
canal.
-Theterminalsectionofthelargeintestineiscalledthe
analcanal.
.

49. Theanalcanal
-Themucousmembraneoftheanalcanalisarrangedin
longitudinalfoldscalledanalcolumnsthatcontainanetworkof
arteriesandveins.
-Theopeningoftheanalcanaltotheexterior,calledtheanus,
isguardedbyaninternalanalsphincterofsmoothmuscle
(involuntary)andanexternalanalsphincterofskeletalmuscle
(voluntary).
-Normallythesesphincterskeeptheanusclosedexceptduring
theeliminationoffeces.

50. Functions of Large Intestine, Rectum and Anal canal
1.Absorption–Inthelargeintestineabsorptionofwater,byosmosiscontinuesuntilthe
familiarsemisolidconsistencyoffecesisachieved.Mineralsalts,vitaminsandsomedrugs
arealsoabsorbedintobloodcapillariesfromthelargeintestine.
2.Microbialactivity–Thelargeintestineisheavilycolonizedbycertaintypesofbacteria,
whichsynthesizevitaminKandfolicacid.TheyincludeEscherichiacoli,Enterobacter
aerogenes,StreptococcusfaecalisandClostridiumperfringens.
3.Massmovement–Thelargeintestinedoesnotexhibitperistalticmovementasinother
partsofthedigestivetract.Onlyatfairlylongintervals(abouttwiceanhour)doesawave
ofstrongperistalsissweepalongthetransversecolonforcingitscontentsintothedescending
andsigmoidcolons.Thisisknownasmassmovement.
4.Defecation –The external anal sphincter is under conscious control through the pudendal
nerve. Defecation involves involuntary contraction of the muscle of the rectum and relaxation
of the internal anal sphincter. When the need to pass faces is voluntarily postponed, it tends
to fade until the next mass movement occurs and the reflex is initiated again.

51. PANCREAS
Thepancreasisapalegreyglandandissituatedintheepigastricand
lefthypochondriacregionsoftheabdominalcavity.
Itconsistsofabroadhead,abodyandanarrowtail.
Theheadliesinthecurveoftheduodenum,thebodybehindthestomach
andthetailliesinfrontoftheleftkidneyandjustreachesthespleen.
Thepancreasisbothanexocrineandendocrinegland.
A.Theexocrinepancreas
-Thisconsistsofalargenumberoflobulesmadeupofsmallacini,the
wallsofwhichconsistofsecretorycells.
-Eachlobuleisdrainedbyatinyductandtheseuniteeventuallytoform
thepancreaticduct,whichextendsalongthewholelengthofthegland
andopensintotheduodenum.
-Justbeforeenteringtheduodenumthepancreaticductjoinsthecommon
bileducttoformtheHepatopancreaticampulla.
Fig. Ducts carrying bile from liver and
gallbladder and pancreatic juice
from pancreas to the duodenum

52. Thefunctionoftheexocrinepancreasistoproducepancreaticjuicecontainingenzymes,someintheform
ofinactiveprecursors,thatdigestcarbohydrates,proteinsandfats.
PancreaticJuice
-Pancreaticjuiceissecretedbytheexocrinepancreasandenterstheduodenumattheduodenalpapilla.
Itconsistsof:
-Pancreaticjuiceisalkaline(pH8)becauseitcontainssignificantquantitiesofbicarbonateions,whichare
alkalineinsolution.
-Whenacidstomachcontentsentertheduodenumtheyaremixedwithpancreaticjuiceandbileandthe
pHisraisedtobetween6and8.
-ThisisthepHatwhichthepancreaticenzymes,amylaseandlipase,actmosteffectively.
Water
Mineral salts
Enzymes (amylase, lipase, nucleases that digest DNA and RNA).
Inactive enzyme precursors (trypsinogen, chymotrypsinogen)

53. FunctionsofPancreaticJuice
1.Digestionofproteins.
2.Digestionofcarbohydrates.
3.Digestionoffats.
ControlofsecretionofPancreaticJuice
-ThesecretionofpancreaticjuiceisstimulatedbysecretinandCCK,
producedbyendocrinecellsinthewallsoftheduodenum.
-Thepresenceofacidicchymefromstomachintheduodenumstimulates
theproductionofthesehormones.
B.Theendocrinepancreas
-Distributedthroughouttheglandaregroupsofspecializedcells
calledthepancreaticislets(ofLangerhans).Theisletshavenoducts
sothehormonesdiffusedirectlyintotheblood.Theendocrine
pancreassecretesthehormonesinsulinandglucagon,whichare
principallyconcernedwithcontrolofbloodglucoselevels.

54. LIVER
Itisthelargestinternalorganandlargestglandofthebody.
Theliverisenclosedinathininelasticcapsuleandincompletelycoveredbyalayerof
peritoneum.Foldsofperitoneumformsupportingligamentsthatattachthelivertotheinferior
surfaceofthediaphragm.
Theliverhasfourlobes–thetwomostobviousarethelargerightlobeandthesmaller,wedge-
shaped,leftlobe;theothertwo–thecaudateandquadratelobes,areareasontheposterior
surface.

55. Theportalfissure
-Thisisthenamegiventotheregionontheposteriorsurfaceoftheliverwherevariousstructures
enterandleavethegland.
-Theportalveinenters,carryingbloodfromthestomach,spleen,pancreasandthesmalland
largeintestines.
-Thehepaticartery(abranchofcoeliacartery),enterscarryingarterialblood.
-Nervefibres,sympatheticandparasympathetic,enterhere.
-Therightandlefthepaticductsleave,carryingbilefromthelivertothegallbladder.
-Lymphvesselsleavetheliver,draininglymphtoabdominalandthoracicnodes.

56. Structure of Liver
Thelobesoftheliveraremadeupoftinyfunctionalunits,calledlobules,.
Liverlobulesarehexagonalinoutlineandareformedbycuboidalcells,the
hepatocytes,arrangedinpairsofcolumnsradiatingfromacentralvein.
Betweentwopairsofcolumnsofcellsaresinusoids(bloodvesselswith
incompletewalls)containingamixtureofbloodfromthetinybranchesofthe
portalveinandhepaticartery.
Amongstthecellsliningthesinusoidsarehepaticmacrophages(Kupffer
cells)whosefunctionistoingestanddestroywornoutbloodcellsandany
foreignparticlespresentinthebloodflowingthroughtheliver.
Blooddrainsfromthesinusoidsintocentralorcentrilobularveins.
Thesethenmergewithveinsfromotherlobules,forminglargerveins,until
eventuallytheybecomethehepaticveins,whichleavetheliverandempty
intotheinferiorvenacava.

57. Oneofthefunctionsoftheliveristosecretebile.
Bilecanaliculirunsbetweenthecolumnsoflivercell.
Thecanaliculijoinuptoformlargerbilecanalsuntileventuallytheyformtherightandleft
hepaticducts,whichdrainbilefromtheliver.
Lymphoidtissueandanetworkoflymphvesselsarealsopresentineachlobule.
Thehepatocytes,bileductsystem,andhepaticsinusoidscanbeorganizedintoanatomicaland
functionalunitsinthreedifferentways:
1.Hepaticlobule
2.Portallobule
3.Hepaticacinus

58. BloodsupplytoLiver
-Thehepaticarteryandtheportalveintakebloodto
theliver.
-Venousreturnisbyavariablenumberofhepaticveins
thatleavetheposteriorsurfaceandimmediatelyenter
theinferiorvenacavajustbelowthediaphragm.
-Theliverreceivesoxygenatedbloodviathe
hepaticarteryandnutrient-richdeoxygenated
bloodviathehepaticportalvein.

59. FunctionsofLiver
-Theliverisanextremelyactiveorgan,whichhasmanyimportant
functionsthataredescribedbelow.
1.Carbohydratemetabolism
-Theliverhasanimportantroleinmaintainingplasmaglucose
levels.
-Carriesoutglycogenesisi.e.glucoseisconvertedtoglycogenfor
storageundertheinfluenceofthehormoneinsulin.
-Later,whenglucoselevelsfall,thehormoneglucagonstimulates
conversionofglycogenintoglucose(glycogenolysis)again,keeping
levelswithinthenormalrange.
2.Fatmetabolism
-Storedfatcanbeconvertedtoaforminwhichitcanbeusedby
thetissuestoprovideenergy.

60. 3.Proteinmetabolism
a.Deaminationofaminoacids–Thisprocess:
•removesthenitrogenousportionfromaminoacidsthatarenotrequiredfortheformationofnew
protein;ureaisformedfromthisnitrogenousportionandisexcretedinurine.
•breaksdownnucleicacidstoformuricacid,whichisexcretedintheurine.
b.Transamination–Removesthenitrogenousportionofaminoacidsandattachesittoother
carbohydratemoleculesformingnewnon-essentialaminoacids.
c.Synthesisofplasmaproteins.–Theseareformedfromaminoacidsandincludealbumins,
globulinsandbloodclottingfactors.
4.Breakdownoferythrocytesanddefenseagainstmicrobes
-ThisiscarriedoutbyphagocyticKupffercellsinthesinusoids.
5.Detoxificationofdrugsandtoxicsubstances
-Theseincludealcohol,wasteproductsandmicrobialtoxins.
-Somedrugsareextensivelyinactivatedbytheliverandarenotveryeffectivewhengivenbymouth
(orally),e.g.glyceryltrinitrate.
-Thisisduetothefirstpassmetabolism.

61. 6.Inactivationofhormones
-Theseincludeinsulin,glucagon,cortisol,aldosterone,thyroidandsexhormones.
8.Secretionofbile
-Thehepatocytessynthesizetheconstituentsofbilefromthemixedarterialandvenous
bloodinthesinusoids.
-Theseincludebilesalts,bilepigmentsandcholesterol.
9.Storage
-Storedsubstancesinclude:
I.Glycogen
II.Fat-solublevitamins–A,D,E,K
III.Iron,Copper
IV.Somewater-solublevitamins,e.g.vitaminB12.

62. CompositionofBile
-Between500and1000mLofbileissecretedbytheliverdaily.Bileconsistsof:
FunctionsofBile
a.Fatdigestion
-Thebileacids,cholicandchenodeoxycholicacid,aresynthesizedbyhepatocytesfrom
cholesterol,thensecretedintobileassodiumorpotassiumsalts.
-Inthesmallintestinetheyemulsifyfats,aidingtheirdigestion.
-Bilesaltsmakecholesterolandfattyacidsmorewater-soluble,enablingboththeseandthefat-
solublevitamins(vitaminsA,D,EandK)tobereadilyabsorbed.
4.Bilepigments,mainlybilirubin
5.Bilesalts
6.Cholesterol
1.Water
2.Mineralsalts
3.Mucus

63. b.Excretionofbilirubin
-Bilirubinisoneoftheproductsofhemolysisoferythrocytesbyhepatic
macrophages(Kupffercells)intheliverandbyothermacrophagesinthe
spleenandbonemarrow.
-Bilirubinisinsolubleinwaterandiscarriedinthebloodboundtotheplasma
proteinalbumin.
-Inhepatocytesitisconjugated(combined)withglucuronicacidandbecomes
water-solubleenoughtobeexcretedinbile.
-Microbesinthelargeintestineconvertbilirubinintostercobilin,whichis
excretedinthefeces.
-Stercobilincolorsanddeodorizesthefeces.
-Asmallamountisreabsorbedandexcretedinurineasurobilinogen.

64. BILIARY TRACT
Bileducts
-Therightandlefthepaticductsjointoformthecommonhepaticductjustoutsidetheportal
fissure.
-Thehepaticductpassesdownwardswhereitisjoinedbythecysticductfromthegallbladder.
-Thecysticandhepaticductsmergeformingthecommonbileduct,whichpassesdownwards
behindtheheadofthepancreas.
-Thisisjoinedbythemainpancreaticductatthehepatopancreaticampulla.
-Itopensintotheduodenum,attheduodenalpapilla,whichiscontrolledbythe
hepatopancreaticsphincter(ofOddi).

65. GallBladder
-Thegallbladderisapear-shapedsacattachedtotheposterior
surfaceoftheliverbyconnectivetissue.
-Ithasafundusorexpandedend,abodyormainpartandaneck,
whichiscontinuouswiththecysticduct.
StructureofGallBladder
-Thewallofthegallbladderhasthesamelayersoftissueasthoseof
thebasicstructureofthealimentarycanal,withsomemodifications:
Peritoneum–Thiscoversonlytheinferiorsurfacebecausetheupper
surfaceofthegallbladderisindirectcontactwiththeliverandheld
inplacebythevisceralperitoneumthatcoverstheliver.
Musclelayer–Thereisanadditionallayerofobliquemusclefibres.
Mucousmembrane–Thisdisplayssmallrugaewhenthegallbladder
isemptythatdisappearwhenitisdistendedwithbile.

66. StructureofBileDuct
-Inthecysticductthemucousmembraneliningisarrangedinirregularcircularfolds.
-Bilepassesthroughthecysticducttwice–onceonitswayintothegallbladderandagain
whenitisexpelledfromthegallbladderintothecommonbileductandthenontothe
duodenum.
BloodsupplytoGallBladder
-Thecysticartery,abranchofthehepaticartery,suppliesthegallbladder.
-Bloodisdrainedawaybythecysticveinthatjoinstheportalvein.

67. FunctionsoftheGallBladder
-Thefunctionsofgallbladderinclude:
•reservoirforbile.
•concentrationofthebilebyupto10-or15-fold,byabsorptionofwaterthroughthe
wallsofthegallbladder.
•releaseofstoredbile.
-Whenthemusclewallofthegallbladdercontracts,bilepassesthroughthebileducts
totheduodenum.
-Contractionisstimulatedbythehormonecholecystokinin(CCK),secretedbythe
duodenumandthepresenceoffatandacidchymeintheduodenum.

68. References:-
RossandWilson,Anatomy&Physiologyin
HealthandIllnessbyAnneWaughandAllison
GrantPublishedbyChurchillLivingstone,12
th
edition.
GerardJ.Tortora&BryanDerrickson,Principles
ofAnatomy&Physiology,PublishedbyJohn
WileyandSons,Inc.,14thedition.
Contributedby–AnkitAjitRoy
Editedby–Pharmacampus