L:\usmle review 7 - Sinoe medical homepage.

esophageal body is also abnormal. A swallow may not induce any peristalsis in the esophageal
body or may produce simultaneous contractions along its entire length.
The esophageal body distal to the diaphragm (choice A) is relaxed in between swallows. The
intraesophageal pressure at this point reflects the intra-abdominal pressure, which is slightly
positive (5 mm Hg). During inspiration, the pressure inside the distal esophagus rises along with
the intra-abdominal pressure; during expiration this pressure falls. The pressure in the
esophageal body proximal to the diaphragm (choice B) reflects the intrathoracic pressure. It is
slightly negative at the end of inspiration and slightly positive at the end of expiration.
Since the mouth and pharynx are open to the atmosphere, in between swallows, the pressure
within the pharynx (choice D) is atmospheric (0 mm Hg). The pressure rises abruptly to a
maximum of 100 mm Hg at the start of a swallow and returns to baseline within 0.5 seconds.
At rest, the pressure in the upper esophageal sphincter (choice E) can be as high as 60 mm Hg.
It is maintained by the normal elasticity of the sphincteric structures, as well as by active
contraction of the cricopharyngeal muscle, which composes most of the sphincter. Shortly after
the pharyngeal muscles contract during a swallow, the upper esophageal sphincter relaxes as the
tonic neural input to the cricopharyngeal muscle (skeletal muscle) is inhibited as part of the
swallowing program. Function of this sphincter is unaffected by achalasia.
7. A 54-year-old man with extensive, severe atherosclerosis sustains a thrombotic occlusion of
the celiac trunk. The organs that receive their blood supply from this artery continue to function
normally. Anastomoses between which of the following pairs of arteries would explain this
phenomenon
(A)
(B)
(C)
(D)
(E)
Left gastric artery and right gastric artery
Left gastroepiploic artery and right gastroepiploic artery
Proper hepatic artery and gastroduodenal artery
Right colic artery and middle colic artery
Superior pancreaticoduodenal artery and inferior pancreaticoduodenal artery