GASTROINTESTINAL TRACT (GIT) .

[ DR.PRATIK KUMAR CHATTERJEE (MBBS;MD;FAGE)

ASSISTANT-PROFESSOR DEPARTMENT OF PHYSIOLOGY KASTURBA MEDICAL COLLEGE (KMC) MANGALORE KARNATAKA ; INDIA ] .

TOPICS TO BE COVEREDTOPICS TO BE COVERED :- :-

(i). FUNCTIONAL ANATOMY .

(ii). SALIVARY GLAND .

(iii). OESOPHAGUS .

(iv). STOMACH .

(v). GASTRO-INTESTINAL (GI) MOTILITY .

(vi). LIVER .

(vii). PANCREAS .

(viii). INTESTINE .

(ix). DIGESTION & ABSORPTION .

(x). GASTRO-INTESTINAL (GI) HORMONES .

[I]. FUNCTIONAL ANATOMY .

TOPICS FOR TODAYTOPICS FOR TODAY :- :-

[I]. [I]. INTRODUCTIONINTRODUCTION . .

[II]. [II]. PROCESSESPROCESSES . .

[III]. [III]. FUNCTIONSFUNCTIONS . .

[IV]. [IV]. COMPONENTSCOMPONENTS . .

[V]. [V]. HISTOLOGYHISTOLOGY . .

[VI]. [VI]. INNERVATIONINNERVATION . .

[VII]. [VII]. MOVEMENTS IN GITMOVEMENTS IN GIT

(FUNCTIONAL TYPES)(FUNCTIONAL TYPES)

[I]. INTRODUCTION :-

(i). Provides the body with the continuous supply of water ; electrolytes & nutrients .

GASTROINTESTINAL (GI) SYSTEM .

[II]. [II]. PROCESSESPROCESSES :- :-

(i). (i). MOVEMENTMOVEMENT food through the food through the alimentary tract .alimentary tract .

(ii). (ii). SECRETIONSECRETION digestive juices . digestive juices .

(iii). (iii). ABSORPTIONABSORPTION water ; various water ; various electrolytes & digestive products .electrolytes & digestive products .

(iv). (iv). CIRCULATIONCIRCULATION blood through blood through thethe

gastrointestinal organs to carrygastrointestinal organs to carry away the absorbed substances .away the absorbed substances .

(v). (v). CONTROLCONTROL functions by functions by local ; nervous & hormonallocal ; nervous & hormonal systems .systems .

[III]. FUNCTIONS :-

(i). DIGESTION ingested food into absorbable molecules .

(ii). SECRETION salivary glands ; pancreas & liver (GI lumen) .

(iii). ABSORPTION nutrients ; electrolytes & water from intestinal lumen into the blood stream .

(iv). MOTILITY propels ingested food from mouth to rectum ; mixes & reduces the size of food .

[IV]. COMPONENTS :-

(i). MOUTH . (ii). PHARYNX . (iii). ESOPHAGUS . (iv). STOMACH . (v). SMALL INTESTINE . (vi). LARGE INTESTINE .

(vii). ACCESSORY ORGANS & STRUCTURES :-

Salivary glands . Tongue . Liver . Gall bladder . Pancreas .

[V]. HISTOLOGY .

(1). POSTERIOR PHARYNX TO ANUS :-

[i]. SEROUS LAYER (SEROSA) :-

Attachment of the gut to the surrounding structures .

[ii]. LONGITUDINAL SMOOTH MUSCLE LAYER .

[iii]. CIRCULAR SMOOTH MUSCLE LAYER :- Mixing & propulsion of contents of the gut .

[iv]. SUBMUCOSAL LAYER :- Loose connective tissue ; blood vessels & lymphatics .

[v]. MUCOSAL LAYER :- Glands ; muscularis mucosa of the smooth muscle ; loose connective tissue in lymphocytes .

• Mucosa

Smooth muscle

Lamina propria

Innermost epithelial cell layer

HISTOLOGY OF THE GIT

(2). FEATURES :-

[i]. Plain muscle & non-striated .

[ii]. Involuntary .

[iii]. [iii]. SINGLE UNIT SMOOTH MUSCLESINGLE UNIT SMOOTH MUSCLE :- :-

(A). Aggregated into sheets or (A). Aggregated into sheets or bundles .bundles .

(B). Syncytial smooth muscle .(B). Syncytial smooth muscle .

(C). Gap junctions .(C). Gap junctions .

[iv]. [iv]. FACTORS THAT DEPOLARIZEFACTORS THAT DEPOLARIZE THE MEMBRANE THE MEMBRANE :-:-

(A). Stretching of the muscle .(A). Stretching of the muscle .

(B). Stimulation by acetylcholine .(B). Stimulation by acetylcholine .

(C). (+) parasympathetic nerves that(C). (+) parasympathetic nerves that secrete acetylcholine .secrete acetylcholine .

(D). (+) specific GIT hormones .(D). (+) specific GIT hormones .

[v]. [v]. FACTORS THAT HYPERPOLARIZEFACTORS THAT HYPERPOLARIZE

THE MEMBRANETHE MEMBRANE :- :-

(A). The effect of norepinephrine /(A). The effect of norepinephrine /

epinephrine on the fiberepinephrine on the fiber

membrane .membrane .

(B). (+) sympathetic nerves that (B). (+) sympathetic nerves that secretesecrete

mainly norepinephrine .mainly norepinephrine .

[VI]. [VI]. MECHANISM OF CONTRACTION & MECHANISM OF CONTRACTION & RELAXATIONRELAXATION :- :-

(A). Smooth muscle doesn’t contain(A). Smooth muscle doesn’t contain

troponin .troponin .

(B). Calmodulin acts as regulatory(B). Calmodulin acts as regulatory

protein .protein .

(C). Myosin kinase & myosin(C). Myosin kinase & myosin

phosphatase play a major role .phosphatase play a major role .

Influx of Ca2+ from ECF

4 Ca2+ ions bind to calmodulin

Ca2+-calmodulin complex Activates myosin kinase

Myosin kinase with ATP phosphorylatesRegulatory chain of myosin head

Myosin head develops Binding capacity

Cycle of attachment & Detachment- contraction

Reduced Ca2+ levels

Activation of myosin phosphatase

Dephosphorylation of Regulatory light chain

Attachment-detachmentCycle stops

Relaxation

[VI]. INNERVATION :-

(i). (i). ENTERIC NERVOUS SYSTEMENTERIC NERVOUS SYSTEM :- :-

(1). (1). LOCATIONLOCATION :- :-

Entirely in the wall ofEntirely in the wall of

the gut (esophagus – anus) .the gut (esophagus – anus) .

(2). (2). NETWORK OF FIBERS (2 TYPES)NETWORK OF FIBERS (2 TYPES) :- :-

[A]. [A]. INTRINSIC INNERVATIONINTRINSIC INNERVATION . .

[B]. [B]. EXTRINSIC INNERVATIONEXTRINSIC INNERVATION . .

(ii). INTRINSIC INNERVATION :-

[1]. [1]. TYPES (2)TYPES (2) :- :-

MYENTRIC PLEXUS / AUERBACH’S MYENTRIC PLEXUS / AUERBACH’S

PLEXUSPLEXUS . .

SUBMUCOSAL PLEXUS /SUBMUCOSAL PLEXUS /

MEISSNER’S PLEXUSMEISSNER’S PLEXUS . .

[2]. LOCATION :--

[3]. (+) MYENTRIC PLEXUS :-

Increased tonic contraction / tone of the gut wall .

Increased intensity of the rhythmical contractions .

Slightly increased rate of rhythm of contractions .

Increased velocity of conduction of excitatory waves along the gut wall

(rapid movement) .

[4]. SIGNIFICANCE :-

(a). MYENTRIC PLEXUS / AUERBACH’S MYENTRIC PLEXUS / AUERBACH’S

PLEXUSPLEXUS motor in function (mainly) . motor in function (mainly) .

(b). (b). SUBMUCOSAL PLEXUS /SUBMUCOSAL PLEXUS /

MEISSNER’S PLEXUSMEISSNER’S PLEXUS sensory in sensory in

function (mainly) .function (mainly) .

(c). (c). CONTROLCONTROL :- :-

Both plexus are interconnected & underBoth plexus are interconnected & under

extrinsic nervous control .extrinsic nervous control .

(iii). EXTRINSIC INNERVATION :-

[1]. SYMPATHETIC NERVE FIBERS :-

(a). Preganglionic sympathetic fibers arise from lateral horns of spinal cord between T-5 & L-2 segments .

(b). Terminate in celiac & mesenteric ganglia .

(c). Postganglionic fibers are distributed throughout the GIT .

(d). (+) motility ; tone ; secretions (stomach) & relaxation of sphincters .

[2]. PARASYMPATHETIC NERVE FIBERS :-

(a). Pass through cranial & sacral nerves .

(b). Synapse with the postganglionic nerve cells in the myentric & submucosal plexus .

(c). (+) motility ; tone ; secretions (stomach) & constrictions of the sphincters .

[VII]. MOVMENTS IN THE GIT (FUNCTIONAL TYPES) :-

(1). PERISTALSIS propulsive movements . (2). MIXING segmentation movements .

THANK YOU .