Large Intestine

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Sections of the Large Intestine

  • Vermiform Appendix
  • Caecum
  • Ascending Colon
  • Right coliac flexure (Hepatic flexure)
  • Transverse Colon
  • Left coliac flexture (Splenic flexture)
  • Descending Colon
  • Sigmoidal Colon
  • Rectum
  • Anal Canal
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Gross structures

Semilunar folds

  • Folds inbetween the Haustra

Taenia Coli 

  • 3 thickened bands of longitudinal muscle

Epiploic Appendages (omental appendicies)

  • small pouches of fat filled Omentum

Haustra

  • Sacculations of the wall between the taenia coli
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Caecum

1st part of the LI

  • Saclike
  • in the right illiac region of the abdominal cavity

Illium opens into its medial aspect from the left of the caecum

  •  superior and inferior iliocolic lips surround the ileal orifice
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Appendix

Vermiform appendix

  • blind ended diverticum
  • point where Taenai coli converge (for surgery)
  • it is supported by the mesoappendix
  • appendix wall contains lots lymphoid tissue (submucosa)

McBurney's Point

  • base of the appendix
  • hexagon
  • McBurneys point lies 1/3 of the way from the ASIS to the umbilicus
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Ascending Colon

  • 12-20cm long
  • Narrower diameter than caecum
  • retroperitoneal
  • covered with peritoneum anteriorly, medially and to some extent laterally

relations

  • S. intestine
  • abdominal wall
  • greater omentum anteriorly
  • Illacus, illiac crest, Quadratus lumborum, lower pole of right kidney posteriorly
  • Hepatic flexure at level of 9th or 10th rib
  • below liver
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Transverse Colon

  • 40cm
  • hangs downward
  • supported by transverse mesocolon - suspended from anterior border of pancrease

Relations

  • Abdominal wall and greater omentum anteriorly
  • 2nd part of duodenum, head of pancreas and jejunum & ileum posteriorly
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Descending Colon

  • From spelenic flexture to pelvic brim
  • 25cm
  • Retroperitoneal
    • anterially
    • laterally
    • peritoneum binds to posterior abdominal wall

Relations

  • small intestine, abdominal wall and greater omentum
  • left psoas major
  • illiacus
  • illiac crest
  • quadratus lumborum
  • lateral border of left kidney posteriorly
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Sigmoidal Colon

  • illiac fossa to S3
  • 25-38cm
  • supported by sigmoidal mesocolon
    • mobile
  • Taeni coli vanish 15cm from anus
    • Longitudinal muscle broadens to form complete layer in rectum
  • Faeces stored in sigmoidal colon just before defaecation

Anterior regions

  • Males; urinary bladder
  • Females; uterus & superior vagina

Posterior regions

  • Rectum and sacrum
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Mesenteries

Ascending, descending, rectum and anus lie outside the peritoneal cavity

Ascending and descending are retroperitoneal

  • They are not supported by mesenteries

However

vermiform appendix, transverse and sigmoidal colons are intraperitoneal

They are supported by 

  • veriform appendix = mesoappendix
  • transverse colon = transverse mesocolon
  • sigmoidal colon = sigmoidal mesocolon

Caecum

is intraperitoneal but is not supported by a mesentery

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Rectum

  • 15cm
  • beguins at S3
  • Follows curve of sacrum and coccyx
  • lies posterior to bladder in men, uterus in women
  • Taeni coli merge to form broad longitudinal muscles anteriorly and posteriorly
  • Mucus membrane form 2 or 3 transverse folds

Pararectal fossae

  • allows movement
  • Terminal part has an anterior dilation called the rectal ampulla
  • ends by peircing pelvic floor
  • Puborectalis forms sling around anorectal junction
  • Important for faecal continence
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Muscles of the Pelvic Floor

Pelvic floor = coccygeus + levator ani

Levator ani = Puborectalis + pubococcygeus + iliococcygeus

Lavator ani must relax to allow urination and defecation

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Anal Canal

  • Vertical nucosal folds "anal columns
  • Internal sphincter (invol)
  • Externa sphincter (vol)
    • Deep = superior
    • superficial = middle
    • subcutaneous = inferior
  • superior part of the canal derived from embryonic hindgut
  • Inferior part of the canal derived from the anal pit
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Blood supply of the Colon

Superior Mesenteric Artery

  • Middle colic
  • right colic
  • Ileocolic
  • Appendicular

Inferior Mesenteric artery

  • Left Colic
  • Sigmoidal branches
  • Superior Rectal
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Innervation

Midgut=

Sympathetic fibres from superior mesenteric plexus,

Parasympathetic fibres form the vagus 

Hindgut=

sympathtic fibres from the inferior mesenteric plexus,

Parasympathetic fibres from plevic splanchnic nerves

Visceral afferent fibres;

T8 - S4

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Imaging of the Colon

Sigmoidalscope

  • Rigid
  • flexible

X-ray

  • chest
  • abdominal

Barium

  • meal
  • enema
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