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An investigation into the structure and function of the ileocaecal junction of the sheep : a thesis presented in fulfilment of the requirements for the degree of Master of Science by thesis only at Massey University
The sheep ileocaecal junction has been shown to have sphincter-like properties, fulfilling the criteria for a gastrointestinal sphincter identified by Fisher and Cohen (1973). However the short zone of elevated pressure within the lleocaecal Junction (ICJ) could be due to venous engorgement rather than tonic muscular activity, as the tip of the ileum examined histologically reveals an irregular musculature interspersed with a vascular loose connective tissue. A similarity is suggested to the human ileocaecal sphincter as described by Quigley, Borody, Phillips, Weinbeck, Tucker and Haddad (1984). This short (less than 5mm) zone of elevated pressure in the sheep would appear to work in conjunction with a valvular action as described by Kuman and Phillips (1987) for the human ICJ, preventing retrograde digesta flow from the caecum to the ileum.
EMG recordings of the ileocaecal region in the conscious sheep showed approximately 70-80% of the MMC phase 3 activity that reaches the distal ileum progresses as far as the ICJ. This appears to be the main motility pattern present in this region in the conscious sheep, and very little coordination was observed between patterns of caecal and ileal activity.
Feeding was found to decrease the amount of MMC activity in the distal ileum by lengthening the interval between successive MMC phase 3 patterns of motility. This effect of feeding on MMC activity appears not to be due to the levels of circulating gastrin, and could be due to either a reflex inhibition such as an intestino-intestinal reflex mediated by noradrenaline as has been described for cats, or humoral mechanisms involving another. agent such as cholecystekinin, VIP or Substance P. Both the latter substances were shown to be present in nervous tissue within the ileum, though their role remains unclear.
