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Large intestine

The caecum and appendix

  • Caecum lies below level of ileocaecal valve
  • Situated in right iliac fossa
  • Completely cover with peritoneum
  • Peritoneal folds create
    • Superior ileocaecal fossa
    • Inferior ileocaecal fossa
    • Retrocaecal fossa
  • Has three longitudinal bands of muscle knows as the teniae coli
  • Converge on base of appendix
  • Anterior relations include the greater omentum and anterior abdominal wall
  • Posterior relations include the psoas and iliacus muscle and femoral nerve
  • Blood supply is from the anterior and posterior caecal arteries
  • These are branches of the ileocolic artery

Appendix

  • Appendix contains a large amount of lymphoid tissue
  • Has a complete covering of longitudinal muscle formed from the teniae coli
  • Base is attached to the posterior medial surface of the caecum
  • Arises below the ileocaecal valve
  • Covered in peritoneum and has a short mesentery known as the mesoappendix
  • Related to anterior abdominal wall one third away along a line joining the anterior superior iliac spine and umbilicus
  • Tip do the appendix can be found in various positions including:
    • Hanging down into the pelvis related to the right pelvic wall
    • Behind the caecum in the retrocaecal fossa
    • Projecting upward along the lateral side of the caecum
    • In front or behind the terminal ileum
  • Blood supply is from the appendicular artery a branch of the posterior caecal artery

The colon

  • The colon is divided into
    • Ascending colon
    • Transverse colon
    • Descending colon
    • Sigmoid colon
  • Blood supply of the colon is as follows
    • Ascending colon is from the ileocolic and right colic arteries
    • Proximal transverse colon is from the middle colic artery
    • Distal transverse colon is from the superior left colic artery
    • Descending and sigmoid colon is from the inferior left colic artery
  • The ileocolic, right and middle colic arteries are branches of the superior mesenteric artery
  • The superior and inferior left colic arteries are branches of the inferior mesenteric artery
  • Venous and lymphatic drainage follows the blood supply

The rectum

  • 15 cm long
  • Begins in front of third sacral vertebra
  • Passes through pelvic diaphragm
  • Continuous with anal canal
  • Peritoneum covers
    • Anterior and later surfaces of upper third
    • Anterior surface only of middle third
  • Lower third has no peritoneal covering
  • Outer longitudinal and inner circular muscle coat
  • Mucous membrane forms three transverse folds

Blood supply

  • Arterial supply if superior, middle and inferior rectal arteries
    • Superior rectal artery is a branch of the inferior mesenteric artery
    • Middle rectal artery is a branch of the internal iliac artery
    • Inferior rectal artery is branch of the internal pudendal artery
  • Venous drainage corresponds to arterial supply
    • Superior rectal vein drains into inferior mesenteric vein
    • Middle rectal vein drains into internal iliac vein
    • Inferior rectal vein drains into internal pudendal vein
  • Site if important porto-systemic anastomosis

Lymphatic drainage

  • Lymphatic drainage is into pararectal nodes
  • Follows superior mesenteric artery to inferior mesenteric nodes

 

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