ألهضمي أمراضألجهاز 2012 \10 \1أالثنين محاضرةبابل \ \ جامعة طب كلية ألطب فرع

. ألشوك منعم د أالستاذ

Anatomy , Physiology & Investigations of Alimentary ( GIT ) tract:

Structure& Function : GIT IS A Tube of 3 main layers:

1 .Inner : mucosa( Squamous in the oesophagus ,Columnar elsewhere ) and surface area of small intestine increased by mucosal folds , villi & microvilli.

2 .Middle muscular layer ( Longitudinal & circular smooth muscles ) inaddition tranverse muscle layer in the stomach , in the colon the longitudinal muscles run in 3 discrete bands ( taenia coli ). And the muscle layer thickens at various points forming valve or sphincter ( LES , Pylorus and ileocaecal valve )

3 .Outer ( Serosa ) layer of connective tissue Oesophagus : ( Cervical , Thoracic and Abdominal ) , 25 cm in length ,there are 4 sites of narrowing of the oesophagus at which foreign bodies may potentially

lodge and the distances is measured from incisors teeth during OGD: The commoncement of oesophagus ( 15 cm. )Level of Aortic Arch ( 22cm. )Level of LMB ( 28 cm. )The Diaphram ( 40 cm. ) Oesophagus :In the Oesophagus Swallowing causes initiation of primary peristalsis waves at the pharynx and relaxation of UOS which push food distally

The closure of UOS is maintained by contraction of cricopharyngeal muscle The LOS tone is high during rest to prevent gastric contents refluxing into

oesophagus .The Sphincter is under vagal & hormonal influences & decrease tone predispose to GOR . Secondary peristalsis is a locally – induced phenomenon that allows food residue to be cleared from the oesophagus and the food bolus culminates in relaxation of LES .The presence of abnormal Tertiary waves can impair peristalsis and typically occurs in elderly. GOR is prevented by:

1 .LES tone ( 20 mmHg ) increased by cholinergic stimulation, Gastrin and presence of food in the stomach.

2 .Acute Angulation of Oesophagus entery into the stomach. 3 .IAP which compresses the abdominal segment of the oesophagus.

4 .Diaphragmatic hiatus5 .Neutralization of acid by swallowed saliva ( 1L \ day )

6 .Valve effects of mucosal folds.

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The Stomach: It is muscular Bag consists of ( epithelium , gastric glands , lamina propria , muscularis mucosa which are inner circular & outer longitudinal layers of muscularis mucosa , submucosa ( BV , & nerves ) then muscularis externa which are inner oblique , middle circular and outer longitudinal layers , then the serosa ( visceral peritoneum . This is important in T – staging of gastric cancer.

Anatomically the stomach divided into: Fundus : ( part of stomach that lies above the cardiac orifice )Body ( main part of stomach )Antrum ( distal portion of the stomach that leads to the duodenum through the pylurous )

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The long gastric curve , the mucosal surface displays thickened folds called Rugae.

The stomach acts as Food Reservoir& is also involved in absorption and mixing of food and initiating emulsification of dietary fat.Parietal cells produce IF & Acid( in response to Gastrin produced by G – cells of gastric antrum , Histamine produced by ELC and vagal nerve stimulation ) ; Chief Cell produces Pepsinogenwhich is converted by acid to pepsin proteases for protein digestion , both these cells types are found within the mucosal

surface of the upper two – third of the stomach . The stomach has to defend itself from digestive secretions and from exogenous agents e.g. ( bacteria , heat , food , cold drugs ) through the protective barrier of gastric mucosa that secretes Mucus , Bicarbonates to neutralizes acids . These defence mechanisms are enhanced by Prostaglandins and Cholinergic Agonists

and decreased by : Alcohol , NSAIDs.

Gastric Acid Secretion

Arterial blood supply:Oesophagus , the upper is supplied by branches of thoracic aorta .The rest of the

gut is supplied by branches of three arteries arising from abdominal aorta: 1 .Coeliac axis ( lower oesophagus , stomach & duodenum )

2 .SMA(Duodenum,small intestine ,colon as far as proximal two thirds of transverse colon )

3 .IMA distal one third of transverse colon , descending and sigmoid colon , rectum and upper two thirds of anal canal.

The watershed area susceptible to ischemia is near splenic flexure between SMA and IMA supplies.

Venous drainage :It is important to know as it is important cause of UGIT & LGIT bleeding .The majority of gut circulation drains via the portal venous system through the liver , returning to the IVC via the hepatic veins,

BrainSight , Smell

Thought

Vagal Stimulation

ACh

Acid

Gastric Distension by Food

Gastrin Secretion

Histamine Secretion

Parietal Cell

IntestineFood

Breakdown

Amino Acid Production

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haematogenous spread of GIT malignancies to the liver via this route is common At the proximal and distal ends of the portal supply venous drainage becomes direct to the systemic system , this allows formation of portosystemic anastomoses and the dilated veins that result at these anastomotic sites (Oesophageal & rectal varies ) may rapture causing causing potentially serious GIT bleeding. Lymphatic Drainage:

The mucosa of GIT is richly supplied with lymphatics draining via submucosal & subserosal plexuses to local LN on the surface of gut . These then drain to nodes beside arteries , eventually back to one of three groups of preaortic nodes around the origin of the three main arteries of the gut (e.g. the stomach is supplied by celiac axis vessels and so its lymphatics drain to celiac axis nodes . )

The upper third of oesophagus drains to cervical LN , the middle third to the Mediastinal LN.

The Rectum and the upper TWO – Thirds of the anal canal drain to the internal & common iliac nodes , the Lower anal canal to superficial inguinal LN.

Rectal & oesophageal cancers pose special problem in GIT Surgery because of potential of wide spread lymphatic spread . In Japan ,there is best Survival rates for Oesophageal & Gastric Cancers – this may reflect their practice of extensive resection of abdominal , Mediastinal and cervical LN with the primary cancers. Nerve Supply:

We have an Enteric NS , the GUT has its own intrinsic neural network , which allows coordination of GIT motility & secretion independent of CNS.

Parasympathetic supply is through the Vagus nerve , and its efferent role in stimulating gastric acid output but 90% of vagal fibers are Afferent (sensory ) .Sympathetic effects on the Gut cause decreased contractility and relaxation of sphincter tone whereas parasympathetic causes the reverse.

Small Intestine: The most important function of small intestine

*Digestion & Absorption *Immunological protection against entery of Ag and\ or Microorgonisms

Neuroendocrine function * *Movements of digestive contents.

Digestion: It is the major organ of absorption and it is 5 – 7 m long . The villi increase the surface area of absorption 20 fold . The ligament of Treitz supports the duodenojejunal flexure , the jejunum is slightly thicker than ileum and has greater number of mucosal folds compared to the ileum.

Peristalsis is initiated by a pacemaker situated in the lower part of the stomach and duodenum and the absorption of nutrients , salts and water is promoted by passive diffusion ( movements from areas of high concentration to low ) , facilitated diffusion ( energy dependent ) and active transport ( which involves the Na \ K ATPase pump )Water and Electrolytes :are usually absorbed from the upper jejunum in combination with monosaccharides and amino acids .However the ileum and right side of the colon may also be involved in regulating this process. In the jejunum Na absorption occurs by:

*Solvent Drag ( water flow – mediated) secondary to monosaccharide absorption

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*Glucose & Amino acids – stimulated active absorption*Bicarbonate – Simulated Na – H Exchange

*Electrogenic active transport

Chloride Absorption: Chloride is absorbed passively down electrical potential and concentration

gradients.In the ileum ,elecroneutral Na – Cl absorption results from parallel ion exchange ( Na – H and HCO3 – Cl )

The process of Water & Electrolytes transport are normally controlled by: 1 .Local neural & paracrine factors

2 .Luminal fatty acids & bile salt concentration In IBD , soluble mediators such as PGs become important in inducing diarrhea , which occurs when there is either reduced intestinal water & electrolytes absorption or increased secretion.

Calcium is absorbed both actively & passively throughout the small intestine> Folate , iron and Vitamins A,B,C, and D are absorbed mainly by jejunum and proximal ileum . B12 and conjugated bile salts are absorbed only by terminal

ileum , surgery or diseases affecting this part of gut may lead: *Vit. B12 malabsorption

*Reduced bile salts recycling , leading to steatorrhea and decreased absorption of fat-soluble vitamins ( A, D,E,and K )

*Diarrhea*Oxalate renal stones

Carbohydrates : Dietary Carbohydrates is mainly Starch and accompanied by sugers such as sucrose and lactose . Starchsare hydrolysed to maltase ( glucose Dimer ) by pancreatic enzymes amylaseand Oligosaccharides then digestion is completed by brush borders enzymes( di- and oligosaccharidases ) to monosaccharides , glucose , galactose & fructose and actively transported using

Na \ K ATPase transport system in the enterocytes .

Protein is initially digested to pepsin in the stomach and then by a number of pancreatic enzymes ( Trypsin , Chymotrypsin , and Elastase ) until it becomes oligopeptides . Thereafter , brush border enzymes peptidases convert oligopeptides into free amino acid which are finally absorbed using many of the available transport systems.

Fat : fat emulsification is initiated within the stomach and continued thereafter by bile salts from contracting gall bladder and dietary and bile juice- derived phospholipids coat fat droplets ,stabilizing the emulsion .Pancreatic Lipase hydrolyzes TG until monoglycerides and fatty acids are produced .Bile salts allow the MG and FA to cross the mucosal surface membrane by creating water – soluble Small aggregates (micelle )or lage aggregates ( Liposomes ).Bile salts are then reabsorbed at the terminal ileum to allow them to enter into the EHC .Within the Enterocytes , Triglycerides are resynthesized & combine with Cholestrol ,Apoproteins ,and phospholipids to form Chylomicrons ,which are transported to the terminal lymphatics & eventually to the general circulation.

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Immunological protection: Gut – Associated lymphoid tissue provide local & systemic protection against antigens & microorganisms .Local immunity is by IgA and to less extent by other Ig and lamina proprial( Neutrophils , Macrophage , Eosinophils ,mast cells and Paneth cells ) at the base of crypts & secrete ( defensins & phospholipase A )

Neuroendocrine Function: APUD system cells share a common embryological origin in the neural crest.secrete the Regulatory peptides are present in the gut & brain and are involved in:

1 .Endocrine ( systemic ) 2 .Paracrine ( local )

3 .neurocrine ( synaptic and peptidergic ) transmission , Which modify gut function .

Conditions associated with raised level

FunctionLocationPeptide

Very high – Gastrinoma ,PA Moderately raised in – RF ,PPI and

vagotomy .

Stimulates Acid release , Gut hypertrophy , Inhibits small gut absorption , Promotes gut motility.

Antral G cells DuodenumPancreas

Gastrin

Stimulates pancreatic enzymes secretion & Gall Bladder contraction

Upper small gut, Colon , Brain

CCK, Pancreozymin

Stimulates pancreatic Bicarbonate secretion

Upper Small GutSecretin

VIPOMAWDHA syndrome

Stimulates small gut secretion

Throughout gut and brain

VIP

Somatostatinoma Inhibits Gastrin ,Insulin ,and Growth Hormone release Inhibits gut motility

Upper gut and Pancreas

Somatostatin

The Colon: Divided into Caecum , Ascending colon ,hepatic flexure , Transverse colon , splenic flexure ,Descending colon , Sigmoid colon , Rectum and anal canal.The appendix is located on the posteromedial wall of caecum . The incomplete outer longitudinal layer of muscularis externa results in Taeniae Coli , which can be seen radiologically as Haustral Pattern , unlike the mucosa of small bowel , large bowel mucosa has no villi and it is flat .The absorption of fluid & electrolytes is

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predominantly regulated in the right side of the colon Colonic Contraction either Segmental for mixing and Propulsive. Contraction are stimulated by entery of ileal effluent into Caecum ,which in turn is controlled by a high pressure zone at ileacaecal valves . When stool enters the rectum this results in relaxation of the of internal anal sphincter and puborectalis muscle . The urge , to defecate is experienced when when a quantity of stool ( perhaps greater than 100ml ) is present in the rectum .The rectum is emptied by relaxation of the external anal sphincter ,which is under voluntary control , increased abdominal pressure may relieve this process .

Roles of Colonic bacteria: *Metabolic ( Ammonia , Bile salts , Drugs e.g.Sulfasalazine )

*Vit. K synthesis*Fermentation of Dietary fibers to short – Chain Fatty acids – these are then

absorbed passively , stimulating Na absorption and providing energy sources for colonic mucosa.

*Modulation of Colonic mucosal function. Changes is colonic flora may lead to alteredfiber digestion ,symptoms of IBS ,and changes in mucosal immunity. Oral Probiotics( Lactobacillus ) used for IBS & IBD. Investigations:

1 .Haematology: )Types of Anemia ,leucocytes , platelets, blood film( ,

2.PT3.Acute phase markers ( ESR , C reactive protein ) and plasma viscosity.

4 .Biochemistry ( B urea , Electrolytes ,Proteins ) LFTs 5.Endoscopy ( OGD , Colonoscopy , ERCP , Enteroscopy , )

Therapeutic & Diagnostic 6 .Radiology:

Plain Radiography , Contrast studies ( Ba swallow , Ba meal , Ba follow through and small bowel enema , Ba enema ),

7 .GIT Angiogrophy 8 .U\S , CT , MRI & MRCP

9 .Radio isotopes study 10 .Functional Tests:

Oesophageal: *pH testing

*Manometry *Bernstein test

Small intestine : Tests for Malabsorption 1 .Stool Analysis ( Fecal Fat )& steatorrhea

2 .14C – triolein Breath test 4 .Pancreatic Function Tests ( Pancreolauryl test for pancreatic fat digestion )

5 .Carbohydrates ( D – Xylose test , GTT , Lactose Tolerance test )6 .Hydrogen Breath test for bacterial overgrowth

7 .Coeliac Serology8.Stool Analysis & culture

9 .Schilling test , B12 & folate level10.75Se HCAT ( Selenium Homo Taurocholate ) for bile acid & bile salts malabsorption

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11.Calcium , Phosphate , Alkaline Phosphatase , Magnesium.12 . Histopathology ( Duodenal biopsy )

Figure Showing Anastomosis of systemic & portal circulation

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