Stomach

Summary

• Function
• Anatomical relations
• Structure
• Neurovascular supply

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Functions

• Enzymatic digestion – formation of chyme from food
• Mechanical digestion

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Location & Anatomical Relations

• Position varies greatly depending on diaphragmatic movement and positional changes

• Anatomical relations:
  • Anterior – diaphragm, left lobe of liver
  • Posterior – omental bursa, pancreas
    • The stomach makes up the anterior border of the omental bursa
  • Superior – left hemidiaphragm, lesser omentum
  • Inferior – transverse colon

• The stomach bed is the resting place of the stomach when supine
  • Diaphragm
  • Spleen
  • Left kidney/adrenal
  • Splenic artery
  • Pancreas
  • Transverse Colon

    

• Surface anatomy
  • Most commonly between the ribs in the supine position

• Position can change with increased/decreased body habitus

  

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Peritoneal relations

• Most of the stomach is intraperitoneal
  • Covered by the greater and lesser omentum

• Lesser omentum:
  • Extends from the lesser curvature around to the greater curvature of the stomach

• Greater omentum:
  • Extends from the greater curvature
  • Folds back to become continuous with the transverse mesocolon
  • Contains the left and right gastroepiploic arteries (which anastomose to form the epiploic arterial arc)

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Structure

• 2 sphincters
  • Superior muscular sphincter = oesophageal sphincter
  • Inferior muscular sphincter = pyloric sphincter

• 4 separate parts:
  1. Cardia – surrounds the cardial orifice (where oesophagus enters)
  2. Fundus
     • Dilated superior part
     • Related to the left hemidiaphragm just under the 5th ICS
     • Separated from oesophagus by the cardial notch
     • Separated by body by the horizontal plane of cardial orificie
  3. Body
     • Lies between fundus and pyloric antrum
  4. Pyloric part
     • Funnel at the end of the stomach
     • Separated from the body by the angular incisure 2/3rds down the lesser curvature
     • It has several sub parts
       • Pyloric antrum – wide part coming from the body
       • Pyloric canal – narrowing after the antrum
       • Pylorus/pyloric sphincter – thickened, distal sphincteric area
         • This controls discharge of chyme into the duodenum via tonic contractions
       • Pyloric orifice – border with duodenum
     • 

       

• 2 curvatures:
  1. Lesser curvature (the superior concave border)
     • Attachment of lesser omentum
  2. Greater curvature (inferior convex border)
     • Attachment of greater omentum

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Layers

 

• Various layers
  1. Mucosal layer
  2. Submucosal layer
  3. External muscular layer (muscularis externa)
     • This itself is made up of 3 muscle layers
     1. Outer longitudinal muscle
     2. Middle circular muscle
     3. Inner oblique layer
  4. Adventitial layer (linked to the parietal peritoneum)

• The stomach is highly distensible to accommodate up to 3 litres of food

• When contracted, the mucosal/submucosal layers form longitudinal folds (rugae)

• The gastric canal is a furrow formed along the lesser curvature during swallowing and communicates fluids
  • Develops due to absence of the oblique layer here

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Neurovascular supply

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Arteries

• Many arteries supply the stomach – all are linked to the celiac trunk which lies superomedial to the lesser curvature
  • 2 arteries supply lesser curvature (Gastric Arteries)
  • 2 arteries supply greater curvature (Gastroepiploic arteries)

1. Left gastric artery
   • One of the 3 branches directly off the coeliac trunk
   • Runs in the lesser omentum until the cardia where it turns back along the lesser curvature
   • Anastomoses with the right gastric around the lesser curvature
2. Right gastric artery
   • Comes off the common hepatic artery (branch of the celiac)
   • Anastomoses with the left gastric
3. Right gastroepiploic (gastro-omental) artery
   • One of the 2 terminal branches of the gastroduodenal artery (along with superior pancreaticoduodenal)
   • Runs along the greater curvature and anastomoses with left GE artery
4. Left gastroepiploic artery
   • Arises from splenic artery
   • Runs along the greater curvature and anastomoses with right GE artery
5. Short gastric arteries
   • A group of 4/5 arteries which supply around the fundus of the stomach
   • Arise from splenic a.

 

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Veins

• Gastric veins follow the arteries in position and course but drain into various larger veins
  • Directly or indirectly will enter the HPV

1. Left and right gastric veins drain directly into the portal vein
2. Short gastric and left gastroepiploic drain into the splenic vein (=> portal vein)
3. Right gastroepiploic drains into the SMV
4. There is also a small prepyloric vein which ascends over the pylorus and drains into the right gastric vein
   • Large in living patients – useful to surgeons identifying the pylorus

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Lymphatic Drainage

• Accompanies arteries
• Ultimately drains into 2 nodes at the stomach curvatures

1. Gastric nodes – at the lesser curvature
   • Take lymph directly from the superior 2/3s of the stomach via vessels accompanying the gastric arteries
   • Also via other nodes
     1. Pancreaticosplenic nodes
        • Drain the fundus along the short gastric and left gastroepiploic arteries
2. Gastro-omental nodes
   1. Pyloric lymph nodes
      • Drain the right 2/3s of the greater curvature
   2. Pancreaticoduodenal nodes
      • Drain the left 1/3 along the short gastric and splenic vessels

• These nodes all drain into the coeliac lymph nodes

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Nerves

• Parasympathetic supply is via direct branches of the anterior/posterior vagal trunks as well as the celiac plexus
  • Anterior:
    • Comes mainly from the left CNX which runs along the anterior oesophagus and lesser curvature where it gives off anterior gastric branches
  • Posterior:
    • Comes from the right CNX and runs along the posterior oesophagus.
    • Gives off 2 branches
      • Gives off a celiac branch which meets the celiac artery and then continues along the lesser curvatures
      • Posterior gastric branches

• Sympathetic supply is via the Greater Splanchnic Nerve (T6-T9)
  • Via the Celiac Plexus
  • Fibres are distributed around the gastric/gastroepiploic arteries