ANATOMY HISTOLOGY PHYSIOLOGY OF STOMACH INCLUDING VAGAL ANATOMY

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• ANATOMY HISTOLOGY PHYSIOLOGY OF STOMACH INCLUDING
  VAGAL ANATOMY

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Stomach

• Roughly J Shaped at rest
• Size and Shape varies with
• a) Volume of food or fluid it contains
• b) Position of body
• c) Phase of respiration
• High and transverse in obese and short persons
• Elongated in thin persons

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Stomach has-

• Two surfaces 1. Anterior 2. Posterior
• Two Curvatures 1.Greater 2. Lesser
• Two Orifices 1. Cardia 2. Pylorus

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Cardia

• Gastro-oesophageal junction
• 2.5 cm. left of midline
• T10 level
• Fundus
• Above the horizontal line from cardiac notch to
  greater curvature.
• In contact with left dome of diaphragm
• Full of swallowed air.

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Incisura

• Junction of horizontal and vertical part of
  lesser curvature
• Clearly seen from inside at endoscopy.
• Pyloroduodenal junction
• Identified by vein of Mayo externally
• Right of midline at L-1

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Stomach bed

• Left crus and dome of diaphragm
• Body of Pancreas
• Splenic artery
• Transverse mesocolon, left colic flexure
• Part of left kidney, left suprarenal.
• Coeliac plexus, ganglion and lymph nodes.

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On Upper GI Endoscopy

• Body and fundus recognized by thick vertical
  mucosal folds
• Incisura seen as transverse ridge
• Antrum by flat mucosa

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Stomach Anatomy on Ultrasound

• Stomach wall thickness 5-6 mm.
• On Endoluminal or laparoscopic ultrasound seen as
  5 layered structure
• Most sensitive method in assessing T component
  of gastric malignancy.

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Stomach Histology

• Three layers
• - Mucosa
• - Submucosa
• - Muscularis Propria

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Mucosa has

• Mucus secreting epithelial cells lining the
  surface and gastric pits.
• Lamina propria containing gastric glands of
  specialised cells.
• Muscularis mucosa dividing mucosa from submucosa.

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Muscularis Mucosa

• Lymphatics cross the muscularis mucosa in the
  stomach to reach lamina propria in contrast to
  colon, where lymphatics do not cross muscularis
  mucosa.
• Hence entity of intramucosal carcinoma in gastric
  cancer.

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Three types of mucosa in stomach

• Cardiac mucosa simple mucus secreting glands,
  circular or oval shaped.
• Body and Fundus - gastric glands are elongated,
  test tube shaped and contain parietal and chief
  cells.
• Antral mucosa Gastric glands are branched and
  secrete mucus and gastrin.

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Histogical division

• Between antrum and body does not correspond to
  anatomical division.
• A tongue of antral mucosa extends up the lesser
  curvature.
• Extent of which increases with age.
• So high gastric ulcers in elderly.
• Foci of gastric metaplasia commonly seen in Ist
  part of Duodenum.

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Cardiac Sphincter

• Not a distinct anatomical sphincter
• Competence maintained by-
• a) Rosette like mucosal fold at G.O. junction
  (plugging action)
• b) Acute angle of entry of lower oesophagus into
  stomach (Valve like effect)
• c) Fixation of G.O. junction by
  phreno-oesophageal ligament.

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Cardiac Sphincter

• d) Presence of lower 3 cm of intra-abdominal
  oesophagus which is compressed by positive
  intra-abdominal pressure.
• e) Circular muscle of the lower oesophagus which
  are thickened.
• f) Right crus of diaphragm acts as a Pinch
  Cock to the lower oesophagus as it pierces it.

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Pyloric Sphincter

• Well defined anatomical structure with a
  physiological mechanism.
• Comprises of outer longitudinal and inner
  circular muscle layer.
• Circular muscle in the shape of inverted V.
• Apex at pyloric end of lesser curvature.
• Limbs spread to greater curvature for 5 cm.
• Longitudinal muscle continuous with the
  longitudinal muscle of Duodenum.

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Blood Supply

• Arterial Supply-
• Left gastric artery - branch of coeliac axis
• Right gastric artery - branch of common hepatic
  artery

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Blood Supply

• Right gastro-epiploic artery - branch of
  gastro-duodenal artery and anastomoses with the
  left gastro-epiploic artery to form an arcade.
• Left gastro-epiploic artery - branch of splenic
  artery.
• Short gastric arteries from splenic artery.

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Clinical Importance

• Gastroduodenal artery passes behind duodenum and
  often gets eroded by overlying duodenal ulcer
  leading to severe haemorrhage.
• Left gastric lymph nodes lie near the origin of
  left gastric artery, so during radical
  gastrectomy, left gastric artery should be flush
  ligated to attain total clearance of lymph nodes.

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Veins

• Veins mainly accompany arteries.
• Left gastric or coronary vein is of surgical
  importance, as it receives branches from
  oesophagus.
• This vein must be divided specifically in
  operations for bleeding oesophageal varices.

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Microcirculation

• Vessels to the mucosa of the lesser curvature
  arise directly from left or right gastric
  arteries instead of submucosal plexus.
• These small vessels take a long course to reach
  mucosa by piercing serosa, muscle and lamina
  muscularis.
• Long course of there vessels and lack of
  submucosal plexus are responsible for the
  development of lesser curvature ischemia more
  often.

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Nerve Supply

• Anterior (Left Vagus)
• Posterior (Right Vagus)

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Anterior Vagus

• At diaphragmatic hiatus, anterior vagus lies
  behind peritoneum and phreno-oesophageal
  ligament.
• Closely applied to anterior surface of
  oesophagus.
• Usually single large trunk.
• In 30 more than one trunk.
• Easily identified by palpation with slight
  tension on oesophagus.
• Often a branch passes to stomach on left side at
  a point 5-7 cm from cardio-oesophageal junction

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Posterior Vagus

• Not applied to the oesophagus
• Separated from it by 10 mm, lies more to the
  patients right.
• Thicker than Anterior Vagus
• May be more than one trunk in 10 of cases.

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Clinical Importance

• Several cms. of Vagal trunks should be excised
  during vagotomy in view of marked capability of
  regeneration autonomic nervous system
• A small artery from Lt. Gastric artery
  accompanies posterior vagus nerve.
• So both ends of divided vagus should be ligated
  while doing posterior truncal vagotomy to avoid
  troublesome bleeding.

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Nerve of Grassi

• Often culprit for incomplete vagotomy.
• It is a branch of posterior vagus, passes behind
  oesophagus to supply gastric fundus.
• Originate at G.O. junction or upto 5-7 cm from
  G.O. junction.
• 5-7 cm. of nerve must be mobilised and any branch
  to the left identified.

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Nerve supply to Pyloric Antrum

• At 7 cm from pylorus, anterior vagus usually
  divides into branches.
• Appearance of this division has been described as
  Crows foot

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Types of Vagotomy

• Truncal Vagotomy
• Nerve trunks are divided above coeliac and
  hepatic branches adjacent to hiatus.
• Selective Vagotomy
• Anterior and Posterior Vagi are divided distal to
  the Coeliac and hepatic branches.
• Extragastric gastrointestinal vagal innervation
  preserved.
• Risk of gallstone formation and diarrhoea less.

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• Highly Selective Vagotomy
• Branches of the anterior and posterior nerves of
  Latarjet to the body of stomach divided at lesser
  curvature.
• Terminal branches to pylorus and antrum
  preserved.

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Functions of Stomach

• Three Major functions
• Motor
• Secretary
• Endocrine

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Motor Functions

• Vagal mediated and gastrin induced receptive
  relaxation.
• Mixing and grinding of food to form chyme.
• Emptying of food at regular intervals.

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Secretary functions

• Secretion of
• Acid
• Pepsin
• Mucus
• Intrinsic Factor
• Water
• Electrolytes.

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Endocrine Functions

• Gastrin, Serotonin, Somatostatin are released
  into blood.

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Physiological functions of Gastric Exocrine
Secretions

• Initiation of peptic hydrolysis of dietary
  proteins and triglycerides (H, Pepsin, Gastric
  lipase)
• Liberation of Vitamin B12 from dietary proteins
  (H, Pepsin)
• Binding of Vitamin B12 for subsequent ileal
  uptake (intrinsic factor).
• Facilitation of Duodenal inorganic Fe and Ca
  absorption (H)

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• Stimulation of pancreatic HCO3 secretion via
  secretion release (H)
• Suppression of antral gastrin release (H)
• Killing or suppression of growth of ingested
  micro-organisms (H)
• Protection against noxious agents (mucin, mucus
  gel)

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Mechanism of Acid Secretion

• When stimulated, parietal cells can secrete HCl
  at a conc. of roughly 160 mM (pH 0.8)
• Acid is secreted in to large canaliculi, which
  are continuous with the lumen of the stomach.
• H ion concentration. In parietal cells is 3
  million fold higher than in blood.
• Chloride is secreted against both concentration
  and electrical gradient.

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• H/K ATPase (proton pump) located in the
  canalicular membrane is the key player in H ion
  secretion.
• This ATPase is Magnesium dependent and not
  inhibited by Ouabin.

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Mechanism of Acid Secretion
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Types of receptors on parietal cells which
stimulates acid secretion

• Histamin receptors (H2) for histamine released
  from enterochromaffin (ECL) and mast cells.
• Muscarinic (M3) type of cholinergic receptors for
  acetylcholine released from postganglionic
  neurons.
• Cholecystokinin (CCKB) receptors for gastrin
  released from G Cells

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Inhibitors of Acid Secretion

• Cholecystokinin
• Sopmatostatin
• Secretin
• Prostaglandin esp. PG2
• Glycagon e.g. peptides
• Gastric inhibitory peptides.
• Peptide YY and enteroglucagon.

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Steps of Acid Secretion in Parietal Cell

• 1. Hydrogen ions are generated within cells from
  dissociation of water
• H2O H OH-
• Hydroxyl ions so formed combine with Carbon
  dioxide to form bicarbonate. This is catalysed by
  Carbonic anhydrase.
• OH- CO2 HCO3-
• Carbonic anhydrase

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1. HCO3 transported out of basolateral membrane in
   exchange for Cl-
2. Outflow of HCO3- from gastric mucosa to blood
   results in alkaline tide
3. Cl- and K transported in to lumen of canaliculus
   by Conductance channels.
4. H ion exchanged with K from cell into lumen of
   canaliculus through the action of proton pump.

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Test for Gastric Acid Secretion

• Basal Acid Output (BAO)
• - Quantity of HCl secreted per hour by the
  stomach in the unstimulated basal state.
• - Expressed as meq of HCl/hour.
• - Normal range 1-5 meq/hour
• - Acid output Volume of gastric juice in
  litres/hour x Conc. of
• H ion (in meq/litre)

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• Maximal Acid Output (MAO)
• - Total acid put during the hour after
  stimulation with pentagastrin (6 mg/kg i.m. or
  s.c. or histamine (40 Mg/Kg s.c.)
• - Value is calculated by adding the results of
  either four 15 minute or six 10 minute sample
  collections after stimulation.
• - Normal range 25-55 meq HCl/hour.

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• 3. Peak Acid Output Two highest consecutive 15
  minute periods of stimulated output, are
  multiplied by a factor of 2 to yield a value for
  a one hour period.
• Gastric secretary studies are useful
• In patients with suspected gastric hyper
  secretion.
• In evaluation of medical and surgical therapy in
  acid peptic disorders.
• In suspected Zollinger Ellison syndrome.

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Effects of Truncal Vagotomy

• Lower Oesophagus
• Pressure in the LOS is reduced
• 10 patients can have transient dysphagia and
  heart burn.
• Stomach
• B.A.O. reduced by 70-80
• M.A.O. reduced by 50-60

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• - Response to standard dose of Pentagastrin
  reduced.
• Loss of receptive relaxation of stomach leading
  to feeling of post-prandial epigastric fullness.
• Gastric mucosal blood flow decreased.
• Reduced rate of gastric emptying for solids, due
  to decreased force of contraction of antral pump.

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• Increased rate of gastric emptying for liquids,
  due to increased intragastric pressure due to
  loss of receptive relaxation of stomach, leading
  to increase in pressure differential between
  stomach and duodenum.
• Biliary System
• Increased fasting gallbladder volume and
  decreased contractility.
• Increased tendency to gall stone formation due to
  bile stasis.

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• Pancreas
• Reduced pancreatic enzyme secretion by 50-70.
• Increased production of Glucagon.
• Small Intestine
• Abnormal proliferation of bacteria in the small
  intestine.
• Reduced absorption of iron calcium.
• Diarrhoea.

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LYMPHATIC DRAINAGE OF STOMACH

• ZONE1-(INF.GASTRIC)
• ZONE2-(SPLENIC)
• ZONE3-(SUP.GASTRIC)
• ZONE4-(HEPATIC)

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