Equine and Porcine Digestive Tract

Nota:

• stomach is small in comparison to the rest of the GI tract and is designed for small and frequent meals

Nota:

• large fermentative caecum and expanded colon structure

1. sensitive pH in colon

   Nota:

   • too much grain/feed = increase in starch in the stomach that reduces the pH and kills microbes, leading to stomach ache

Nota:

• byproducts of digestion and so there isn't time to absorb these nutrients before they are passed out of the colon

1. relatively small
2. Large non-glandular region

   Nota:

   • dirty white in color
   • high pH and lack of digestion/glandular excretion means that botfly larvae can thrive here and are often seen via larvae carcasses or the holes of burrows within the fundus
   1. saccus caecus/fundus
   2. stratified squamous epithelium
   3. blind sac
   4. high pH
3. Glandular Region

   Nota:

   • yellowish in color
   1. fundic

      Nota:

      • production of acid and gas
   2. simple columnar epithelium
4. Margo Plicatus

   Nota:

   • pleated margin/ridge that separates the two regions of the stomach
5. well developed oblique cardiac sphincter

   Nota:

   • unable to vomit
   • can cause gastric dilation due to a build up of gas and fermenting/non broken down ingesta

1. sickle shaped

   Nota:

   • base, apex, cranial and caudal border
2. curved apex points cranially, found ventrally
3. hilus found on the visceral side
4. left side of the abdomen
5. nephrosplenic ligament

   Nota:

   • attaches the spleen to the left kidney
6. gastrosplenic ligament

   Nota:

   • attaches the spleen to the stomach, found within the greater omentum on the gastric surface

1. right side of the abdomen
   1. mesenteric attachment to dorsal body wall

      Nota:

      • patch of dorsal caecum is retroperitoneal
   2. apex associated with xiphoid process
   3. base near right paralumbar fossa
   4. comma shaped
2. all ingesta passes through
3. ileocaecal and caecocolic junctions

   Nota:

   • ileum opens directly into the caecum (ileocaecal fold within the mesentery)
4. 4 taeniae

   Nota:

   • longitudinal muscular bands across the structure, creates sacculations/haustra
5. large fermentation vat

   Nota:

   • main site of fermentation in the horse

Nota:

• Large Colon = ascending Small Colon = transverse and descending

1. Ascending
   1. Right Ventral Colon
      1. up to sternal flexure

         Nota:

         • right up to the diaphragm
      2. 4 taeniae
   2. Left Ventral Colon
      1. up to pelvic flexure

         Nota:

         • free standing and doesn't attach to anything
      2. 4 taeniae
      3. narrowing at flexure
      4. intercolic ligament only

         Nota:

         • the LVC and LDC are only attached to each other by the intercolic ligament and so are very mobile within the abdomen
         • commonly prone to left colon displacement as a result of increased mobility
   3. Left Dorsal Colon
      1. 1 taeniae at flexure
      2. 3 taeniae cranially

         Nota:

         • band widens from the narrow pelvic flexure
      3. up to diaphragmatic flexure

         Nota:

         • sits dorsal to the sternal flexure
   4. Right Dorsal Colon
      1. up to transverse colon
      2. 3 taeniae
2. Descending
   1. 3 taeniae
   2. left side

1. caudal third of the abdomen
2. Aorta
3. Base of the Caecum
4. Pelvic Flexure
5. faecal balls in descending colon
6. LVC and LDC

   Nota:

   • with intercolic ligament between them
7. Caudal pole of the Spleen
8. Left Kidney

   Nota:

   • only the caudal aspect of the kidney in smaller horses
9. Nephrosplenic Ligament

   Nota:

   • should be able to feel the ligament and a space between the spleen and kidney (common site of left colon displacement)
10. Root of Mesentery

    Nota:

    • if the mesojejunoileum is twisted, the root of the mesentery will feel very rigid and out of place
11. only feel small intestines if dilated

1. monogastric
2. greater omentum is not very developed and has no yellow color

   Nota:

   • no tunica flava: doesn't have the same yellow elastic fibres as seen within other large animal abdominal anatomy
   • greater omentum not seen upon incision as it has not attachments to the intestines and abdominal floor
3. Non Glandular Region
   1. stratified squamous epithelium
   2. Left Side of the Abdomen

      Nota:

      • fundus and corpus on left side, related to the liver and diaphragm
4. Glandular Region
   1. simple columnar glandular epithelium
   2. Cardiac
   3. Diverticulum

      Nota:

      • projects caudally from the fundus, species specific
5. Torus Pyloricus

   Nota:

   • narrows the pyloric canal
   • extends within the pylorus to the right side of the abdomen

1. base near left kidney
   1. sweeps ventrocaudally onto left side

      Nota:

      • species anomaly, all other species have a caecum on the right hand side
      • moves along left flank
2. 3 taeniae

1. development
   1. twisting of colon and jejunoileum
   2. ascending colon twists independently

      Nota:

      • into a conical spiral around its mesentery
   3. limbs develop at different rates

      Nota:

      • as different limbs of the ascending colon develop at different rates, it causes the vortex or conical spiral to be created
2. Ascending
   1. lies against left flank
   2. cone points ventrally towards the abdominal floor
   3. Centripetal Coils
      1. proximal
      2. outer turns
      3. wide and sacculated
      4. descending dropping down into te vertex
   4. Centrifugal Coils
      1. distal
      2. inner turns
      3. narrow and smooth
      4. tighter coils
      5. emerge dorsally, pass to the right of the root of the mesentery
      6. ascending curling up to the roof of the abdomen
   5. 2 taeniae

1. lies under LHS caudal ribs
2. gastrosplenic ligament

   Nota:

   • attaches the spleen to the stomach
3. contact with diaphragm

   Nota:

   • on the parietal surface
4. ventral/caudal emergence from costal arch