Nerve suppy to the large intestine

The ascending colon, and most of the transverse colon, are innervated by the parasympathetic vagus nerve. The remaining segments receive parasympathetic innervation via branches of the sacral nerves and sympathetic innervation via

Internal anal sphincter

(involuntary)

Anal canal

External anal sphincter (voluntary)

Rectum

Anu5

Anal column

Figure 6.2 Arrangement of the anal sphincters. This material is used by permission of John Wiley & Sons, Inc. From G.J. Tortora et al. Principles of Anatomy and Physiology, 8th edition (1996).

Anu5

Internal anal sphincter

(involuntary)

Anal canal

External anal sphincter (voluntary)

Rectum

Anal column

Figure 6.2 Arrangement of the anal sphincters. This material is used by permission of John Wiley & Sons, Inc. From G.J. Tortora et al. Principles of Anatomy and Physiology, 8th edition (1996).

the spinal nerves. Stimulation of parasympathetic nerves increases intestinal contraction and the production of mucus. Conversely stimulation of sympathetic nerve fibres inhibits colonic secretions and motility and stimulates the rectal sphincter.

Afferent sensory nerve fibres are present in the mucosa, submucosa and muscular layers of the colon. The colon is insensitive to painful stimuli but is sensitive to changes in pressure. Stretching of the colon as a result of overdistension can result in abdominal pain, but removal of lesions, such as colonic polyps, can be achieved painlessly without anaesthetic.

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