660 Chapter 18
- Identify the different neurons present in the wall of the
intestine and explain how these neurons are involved
in “short reflexes.” Why is the enteric nervous system
sometimes described as an “enteric brain?” - Trace the course of blood flow through the liver and discuss
the significance of this pattern in terms of the detoxication of
the blood. Describe the enzymes and the reactions involved
in this detoxication. - Drugs taken to treat gastritis and gastroesophageal reflux
include proton pump inhibitors, H 2 histamine receptor
blockers, and buffers. Give examples of each type of drug
and explain how they may help. - Describe the reflexes controlling the stomach, liver,
gallbladder, and pancreas that are triggered by the arrival of
chyme in the duodenum. - Describe the intestinal microbiota, their location, and the
possible benefits they may confer.
Test Your Analytical Ability
- Which surgery do you think would have the most
profound effect on digestion: (a) removal of the stomach
(gastrectomy), (b) removal of the pancreas (pancreatectomy),
or (c) removal of the gallbladder (cholecystectomy)? Explain
your reasoning. - Describe the adaptations of the GI tract that make it more
efficient by either increasing the surface area for absorption
or increasing the contact between food particles and
digestive enzymes. - Discuss how the ECL cells of the gastric mucosa function
as a final common pathway for the neural, endocrine, and
paracrine regulation of gastric acid secretion. What does this
imply about the effectiveness of drug intervention to block
excessive acid secretion? - Bacterial heat-stable enterotoxins can cause a type of
diarrhea by stimulating the enzyme guanylate cyclase, which
raises cyclic GMP levels within intestinal cells. Why might
this be considered an example of mimicry? How does it
cause diarrhea?
36. The hormone insulin is secreted by the pancreatic islets
in response to a rise in blood glucose concentration.
Surprisingly, however, the insulin secretion is greater in
response to oral glucose than to intravenous glucose. Explain
why this is so.
37. The bacteria that are part of the intestinal microbiota are
usually described as commensal bacteria. What does this
mean? Present arguments that the relationship is more an
example of mutualism.
38. A drug swallowed as a pill or capsule may not make it into
the general circulation in sufficient amounts to be effective.
Explain different mechanisms that may account for this
observation. Why might a drug delivered by a skin patch
or nasal spray be more effective than the same drug taken
orally?
39. Explain the relationship between blood and the liver’s
detoxication enzymes, and the possible relationship
between the liver’s detoxication enzymes and the American
Revolution.
Test Your Quantitative Ability
Refer to figure 18.14 to answer the following questions.- What is the frequency of slow-wave production per minute
indicated in this figure? - About how long does each slow wave last (what is its
duration)? - Each slow wave and action potential represents a total
depolarization of how many millivolts (mV)? - Each slow wave has a depolarization (not counting the action
potential) of about how many millivolts (mV)?
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