Clinical Note

Diabetic Autonomic Neuropathy

A significant percentage of patients with diabetes mellitus exhibit a syndrome described as diabetic autonomic neuropathy. The neuropathy involves the loss of preganglionic and postganglionic autonomic nerve fibers and is characterized by hypotension upon standing, constipation and/or diarrhea, decreased gastric emptying, impotence, and abnormal sweating. The etiology of the disorder is not known; however, both metabolic defects and defects in blood flow to the nerves have been implicated.

FIGURE 8 Simplistic representation of the neural plexuses of the enteric division of the autonomous nervous system, located within the small intestine (see Chapter 32, Fig. 3, for more detail).

than in the spinal cord. The enteric system is in turn innervated by the sympathetic and parasympathetic divisions. This extrinsic innervation appears to serve primarily a modulatory function to alter the intrinsic activity of the enteric neural network.

The intrinsic activity of the enteric nervous system (ENS) is important in regulating most of the functions of the gastrointestinal system. For example, during fasting, contents of the stomach and small intestine are swept toward the colon by a complex of contractions that periodically starts in the stomach and systematically progresses along the length of the bowel. This migrating motor complex cycles such that a new one begins in the stomach approximately every 90 minutes. This entire pattern of spatiotemporal contractions of the intestinal musculature is produced and controlled by the ENS. Immediately after ingestion of a meal, a fed pattern of intestinal contractile activity is generated. It appears that this pattern also is preprogrammed within the ENS and that it is activated by hormones such as cholecystokinin, interacting with command neurons within the intrinsic neural plexuses. Cholecystokinin is released by the intestine in response to the meal. Both the migrating motor complex and the fed pattern of contractile activity are modulated by the sympathetic and parasympathetic components of the autonomic nervous system.

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