chorda tympani. The Xth (vagus) cranial nerve (answer d)innervates taste
buds on the epiglottis and palate. The XIIth (hypoglossal) cranial nerve
innervates the intrinsic musculature of the tongue (answer e).
206.The answer is e.(Kasper, pp 231–232, 300, 449. Junqueira, p 282.)
Hirschsprung’s disease (congenital megacolon) and Chagas’ disease have
different etiologies, but both inhibit intestinal motility by affecting the
myenteric (Auerbach’s) plexus located between the layers of the muscularis
externa (layer e) in the figure. The submucosal (Meissner’s) plexus is more
involved in regulation of lumenal size and, therefore, will affect defecation,
but will be less involved in peristalsis. Vascular smooth muscle, the mus-
cularis mucosa, and enteroendocrine cells do not play a major role in the
regulation of peristalsis, which is observed even after removal of the gut
and placement in a nutrient solution. Hirschsprung’s disease, also known
as aganglionic megacolon, results from failure of normal migration of
neural crest cells to the colon, resulting in an aganglionic segment.
Although both the myenteric and submucosal plexuses are affected, the pri-
mary regulator of intrinsic gut rhythmicity is the myenteric plexus. Chagas’
disease is caused by the protozoan Trypanosoma cruzi.Severe infection
results in extensive damage to the myenteric neurons.
The wall of the GI tract contains four layers: mucosa, submucosa,
muscularis externa, and serosa. The structure labeled ain the photomicro-
graph is the lamina propria, a loose connective tissue layer immediately
beneath the epithelium. Also part of the mucosa is a double layer of smooth
muscle cells (layer b) comprising the muscularis mucosa. In the photomi-
crograph, an inner circular and outer longitudinal layer of smooth muscle
cells is discernible. A thick layer of dense irregular connective tissue, the
submucosa (layer d), separates the muscularis mucosae from the muscu-
laris externa. The structure labeled c is a nest of parasympathetic postgan-
glionic neurons forming part of Meissner’s plexus. The muscularis externa
(labeled layer e) generally consists of inner circular and outer longitudinal
layers of smooth-muscle cells. Slight variations in these components may
occur in specific organs of the GI tract. The respiratory, urinary, integu-
mentary, and reproductive systems differ from the gastrointestinal system
in their epithelia and arrangement of underlying tissue.
207.The answer is a.(Avery, pp 306–310. Guyton, pp 740–741.)The
woman in the scenario suffers from Sjögren’s syndrome, which like other
Gastrointestinal Tract and Glands Answers 331