Large Intestine

• Main differences b/W small and large intestine

  1. Epiploic appendages
  2. Teniae Coli - incomplete outer layer except appendix and rectum they dont have it
  3. Sacculations (Haustra)
• The peritoneum at the cecum fuses with posterior abdominal wall to form rectocecal recess
• The sigmoid colon has its own mesentry
• Ileum to cecum (2.5 inches) junction is called illeocecal valve/lips and appendix to cecum it forms orrifice of (vemiform of appendix)

  There is one inch between orifice of appendix and ileocecal valve
• Appendix has a false mesentery called mesoappendix and the artery that supplies the appendix is caleld appendicular artery which is a branch from ileocolic
• Tenia of cecum

  1. anterior
  2. one posteromedial
  3. one posterolateral which opens into cecum at the appendical openin

  
• The length of the appendix is 2-4 inches but can vary from 1-8 inches
• Positions of the appendix

  1. retrocecal - 11 clock -65%
  2. Pelvic -5 clock- 32%
  3. Paracolic - 2%
  4. Antileal - 0.5%
  5. Retroileal - 0.5%

  
• Ascending colon

  1. 5 inches long
  2. retroperitoneal organ
  3. Right colic/hepatic flexure which is lower than left because of the liver
• Transverse colon

  1. 15 inches
  2. transverse to the posterior abdominal wall crosses second part of duodenum and pancreas
• Right coli flexure between inferior surface of the right lobe of the liver and anteiror surface of the lower part of the kidney
• Left colic/Splenic flexure

  1. phernico-colic ligament - supports the spleen
  2. Flexure is found over the anterior surface of the left kidney and superiorly it is in contact with visceral surface of the spleen close to its lower pole
• Sigmoid colon (10-15 inches)

  Completely invested in the peritoneum - which hands on a free mesentry (Sigmoid mesocolon)

  The mesocolon attaches to peritoneum of posterior pelvic wall - making an inverted V shape

  Apex at the bifurcation of the left comon iliac artery in front of the left ureter with the inferior mesentric vessels medial to it
• Rectum (5 inches) starts at the S3

  Applied to sacrum and coccyx (where it ends ) which lateron pierces the pelvic floor to become continous with the anal canal

  The lower part is dilated to form the ampulla

  Doesnt have proper mesentery - posterior - retroperitoneal
• 4 differences between rectum and sigmoid

  1. haustrations
  2. Appendices epiploicae
  3. taenia coli
  4. Sidmoid mesocolon ceases indicated that is the upper part of rectum
• Muscular coat of the rectum: merging of the 3 teniae coli to form a broad band on the anterior and posterior surfaces
• Puborectalis muscle - a portion of levator ani

  forms a sling at the junction of rectum with anal canal > forming the anorectal angle (last 4 cm of anal canal)
• Transverse folds (valves of houstun) [3 in number - semicircular folds] = mucous membrane + inner circular muscular layers
• Peritoneal relations of the rectum

  1. Upper third is covered by peritoneum anteriorly and on both sides
  2. Middle third of rectum is covered by peritoneum ONLY ANTERIORLY
  3. Lowest third not covered by peritoneum at all
• Anterior Relations of Rectum

  Male:

  Upper 2/3 is related to coils of intestine that occupy the pouch of douglas

  Lower 1/3 is seperated from the bladder prostate and vas deferences and seminal vesicles by denonvilliers fascia

  
• Anterior Relations of Rectum

  Female:

  Upper 2/3 is related to the coils of intestine that occupy the pouch of douglas

  lower 1/3 is seperated from vagina by denonvilliers fascia
• Posterior relations of the rectum

  2 bones (sacrum and coccys)

  2 muscles (piriformis and coccygeus)

  2 nerves (sympathetic and parasympathetic)

  2 vessels (median sacral and superior rectal)
• Anal Canal (4 cm long)

  Pases downward and backward from rectal ampulla to the anus

  Posteriorly it is related to the anococcygeal body

  Anteriorly it is related to the perineal body

  
• Upper half of the anal canal comes from hindgut endoderm and it has columnar epithelium
• In the upper half

  Anal columns of morgagni exist where each of them carry a small artery and vein (internal rectal plexus > internal haemorhoids)
• Pectinate (dentate) line is made of all the anal sinus it demonstrates the end of upper half and start of lower half of the anal canal

  
• Upper half of anal canal

  Hypogastric plexuses

  Senstivie to stretch

  Superior rectal vessels for blood supply

  Pararectal and inferior mesentric lymph nodes
• The pudendal nerve is responsible for the sensory innervation in anal canal
• For upper half of anal canal

  Superior rectal vein > inferior mesenteric vein (portal venous system).
• Lower half of anal canal comes from ectoderm > has stratified squamous epithelium
• Lower half

  Somatic innervation (inferior rectal nerve) > sensitive to pain
• Arterial supply of lower half of rectal canal

  inferior rectal artery a branch of internal pudendal artery

  Venous drainage is by inferior rectal vein a tributary of internal pudendal vein which drains into internal iliac vein to IVC
• Lymph drainge of lower half of rectal canal is to the medial group of superficial inguinal nodes
• Internal anal sphincter is involuntary

  Upper two thirds of anal canal (up until hiltons white line which is a thickened lower end of the inner circular muscular layer of the gut)

  Innervation is from the inferior hypogastric plexus
• External Sphincter is voluntary

  Tube of striated muscle which surrounds the entire length of anal canal

  made up of three rings

  1. Subcutaneous part: lower end of anal canal, no bony attachments, seperated from the skin by corrugator cutis ani muscle which is smooth muscle that radiates out from hiltons line
  2. Superficial which is attached to the coccyx behind the perineal body
  3. Deep part which encircles the upper part and has no bondy attachments > fuses with fibres of puborectalis of the two sides
• External sphincter is supplied by inferior rectal nerve > pudendal nerve > peineal branch of S4
• External Sphincter

  Deep part > fuses with puborectalis

  Superficial Part > coccyx to perineal body

  Subcutaneous part
• Anal continence is depndent on 5 structures

  1. Internal anal sphincter
  2. External anal sphincter
  3. Puborectalis sling
  4. Anal columns (of morgagni)
  5. Transverse folds of the rectum (valves of houston)