Which of the following regions of the GI tract are the most dependent on extrinsic nerves for regulation?
Lower esophagus and distal stomach
Lower esophagus and proximal stomach
Small intestine and large intestine
Upper esophagus and distal stomach
Upper esophagus and external anal sphincter
The correct answer is E.
E. The upper esophagus and the external anal sphincters are composed of striated muscle that has no intrinsic activity and depends on extrinsic innervation to regulate its contractions. The lower esophagus, distal stomach, small intestine, and colon are composed of smooth muscle and are innervated by enteric nerves that impart a high degree of independence from extrinsic nerves. The proximal stomach is intermediate in its dependence, with receptive relaxation being impaired by vagotomy.
A 30-year-old woman comes to the doctor’s office complaining of progressively worsening difficulties with swallowing. A manometric study is conducted to examine pressure generation along the length of her esophagus. This test reveals that contractions in response to a swallow are poorly synchronized and pressure in the lower esophageal sphincter remains elevated. Production of which of the following neurotransmitters is likely to be reduced at the level of the lower esophageal sphincter?
The correct answer is D.