Colon - Anatomy & Physiology

From WikiVet English
Jump to navigation Jump to search
BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY
BACK TO LARGE INTESTINE - ANATOMY & PHYSIOLOGY

Introduction

The colon can be divided into the following portions:

  • Ascending
  • Transverse
  • Descending

Structure

The following anatomocial arrangement is found only in cats and dogs, see species differences.

  • The ascending colon continues from the iluem at the ileocolic junction.
    • It runs to the right of the cranial mesenteric artery in a caudal to cranial direction.
    • At the cranial border of the mesentry it turns medially to become the transverse colon.
  • The transverse colon runs from the right side of the abdomen to the left side of the abdomen.
    • Cranial to the transverse colon is the stomach, and caudal to it is the small intestine and cranial mesenteric artery.
  • The descending colon continues on from the transverse colon running caudally on the left from the level of (???).
    • It then passes more medially as it enters the pelvic cavity
    • Upon entering the pelvic cavity it is continued as the rectum.

Function

Vasculature

Innervation

Lymphatics

Histology

Colon (fox) - Copywright RVC 2008
  • Mucosa has a columnar epithelium.
    • Mucosa is thick.
    • Mucosa has long glands.
  • Submucosa has large lymphatic nodules which may interrupt the lamina muscularis.
  • Lamina muscularis is incomplete.

Species Differences

Ruminant

  • The ascending colon is the longest part of the colon and is composed of three parts:
    • Ansa proximalis
      • Has a sigmoid flexure that passes around the caudal border of the mesentry to the left side of the root of the mesentry.
    • Ansa spiralis
      • Consists of two centripetal turns and two centrifugal turns in the ox.
        • There are three turns in the sheep and four in the goat.
        • In the ox, the ansa spiralis is a flat disc, whilst in the small ruminants it takes the form of a cone.
    • Ansa distalis
      • Goes back around the caudal border of the mesentry, to the right side of the root of mesentry.
      • It then passes cranially adjacent to the mesentry until it reaches the cranial border of the mesentry.
  • The transverse colon crosses the midline of the abdomen, from right to left at the cranial border of the mesentry.
  • The descending colon continues caudally to the rectum and anus.
    • It has a sigmoid flexure before it enters the pelvic cavity.
  • Development
    • The ox's ascending colon expands caudally around the root of the mesentry on the left side of the mesentry (compare to horse, where it expands cranially).

Horse

Pig

  • The arrangement of the transverse and descending colon is similar to that of the dog and cat, but the ascending colon is different.
    • The ascending colon is elongated and coiled to form a cone-shaped organ.
    • The base of the cone is attached to the dorsal abdominal wall and the apex points ventrally.
    • The position of the ascending colon varies with filling of the stomach.
    • From the caecum, there are clockwise centripetal turns to the apex of the cone.
    • Then the centrifugal turns run anti-clockwise on the inside of the cone.
      • Centripetal turns have two taenia, whilst centrifugal turns have none.

Links