Bowel

Divisions

• Esophagus

  • Cervical and thoracic segments

• Stomach

  • Hollow muscular organ between esophagus and small intestine

  • Location: Intraperitoneal, in left upper quadrant, bordered superiorly by left hemidiaphragm, posterolaterally by spleen, posteroinferiorly by pancreas

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      Greater omentum attached from greater curvature and drapes over small and large intestines

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      Lesser omentum attached from lesser curvature to porta hepatis, covers lesser sac

  • Function

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      Gastric acid production for breakdown of large molecules of food into smaller molecules in preparation for small intestinal absorption

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      Storage of food

  • Sections

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      Gastroesophageal junction/cardia, lower esophageal sphincter

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      Fundus and body: Delineated by horizontal plane passing through cardia

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      Antrum/pylorus: Lower section facilitating entry of gastric contents into duodenum

  • Curvatures

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      Greater curvature: Lateral wall of stomach

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      Lesser curvature: Medial wall of stomach

  • Rugae/internal ridges increase surface area for digestion

  • Arterial supply

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      Right and left gastric arteries supply lesser curvature

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      Right and left gastroepiploic arteries supply greater curvature

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      Short gastric artery supplies fundus

  • Venous drainage

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      Follow arteries and drain into portal vein and its tributaries

• Small bowel

  • Between stomach and large intestine

  • ~ 4-7 meters in length

  • Centrally located in abdomen

  • Intraperitoneal, except for 2nd-4th portions of duodenum

  • Function: Further breakdown of food molecules from stomach with eventual absorption

  • Intraluminal extensions/folds valvulae conniventes increase surface area for absorption

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      Abundant in proximal small bowel, decrease in number in distal small bowel loops

  • Duodenum

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      C-shaped hollow tube connecting stomach with jejunum

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      Begins with duodenal bulb, ends in ligament of Treitz (duodenojejunal junction)

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      Arterial supply and venous drainage: Superior and inferior pancreaticoduodenal artery, pancreaticoduodenal veins

  • Jejunum

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      Connects duodenum with ileum

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      ~ 2.5 meters in length

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      Begins at ligament of Treitz

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      Along with ileum, suspended by mesentery

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      Arterial supply and venous drainage: Superior mesenteric artery and vein

  • Ileum

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      Connects jejunum with ascending colon

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      ~ 3.5 meters in length

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      Along with jejunum, suspended by mesentery

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      Arterial supply and venous drainage: Superior mesenteric artery and vein

• Large bowel

  • Between small bowel and anus

  • ~ 1.5 meters in length

  • Peripherally located in abdomen

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      Cecum and appendix, transverse colon, and rectosigmoid intraperitoneal

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      Ascending colon, descending colon, and middle rectum retroperitoneal

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      Distal rectum extraperitoneal

  • Function: Absorption of remaining water, storage, and elimination of waste

  • Sections

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      Ascending colon: Located in right side of abdomen, includes cecum where appendix arises

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      Hepatic flexure: Turn of colon at liver

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      Transverse colon: Traverses upper abdomen

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      Splenic flexure: Turn of colon at spleen

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      Descending colon: Left side of abdomen

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      Sigmoid/rectum: At posterior pelvis

  • With taenia coli: 3 bands of smooth muscle just under serosa

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      Haustration: Sacculations in colon resulting from contraction of taenia coli

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      Epiploic appendages: Small fat accumulations on viscera

  • Arterial supply

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      Superior mesenteric artery supplies colon from appendix through splenic flexure

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      Ileocolic branch supplies cecum

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      Right colic branch supplies ascending colon

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      Middle colic branch supplies transverse colon

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      Inferior mesenteric artery supplies descending colon through rectum

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      Left colic branch supplies descending colon

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      Sigmoid branches supply sigmoid

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      Superior rectal artery supplies superior rectum

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      Middle and inferior rectum supplied by arteries of same name originating from internal iliac artery

  • Venous drainage

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      Superior and inferior mesenteric veins

• Anus

  • External opening of rectum

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      Termination of gastrointestinal tract

  • With sphincters for controlling defecation

  • Internal anal sphincter

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      Thin ring of smooth muscle surrounding anal canal, deep to submucosa

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      Under involuntary control

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      Continuous with muscularis propria of rectum

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      Forms incomplete ring in females

  • External anal sphincter

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      Thick ring of skeletal muscle around internal anal sphincter

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      Under voluntary control

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      3 parts from superior to inferior: Deep, superficial, and subcutaneous

  • Longitudinal muscle

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      Thin muscle between internal and external anal sphincters

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      Conjoined muscle from muscularis propria of rectum and levator ani