542
Chapter 15
stimulates pancreatic bicarbonate secretion, whereas CCK
is a weak stimulus of bicarbonate secretion. Both hormones
together, however, stimulate pancreatic bicarbonate secretion
more strongly than would be predicted by the sum of their
individual stimulatory effects. This is because CCK amplifi es
the response to secretin. One of the consequences of potentia-
tion is that small changes in the plasma concentration of one
gastrointestinal hormone can have large effects on the actions
of other gastrointestinal hormones.
Many other peptide hormones that have recently been
described are released by or infl uence gastrointestinal func-
tion.
Leptin
is released from fat cells and infl uences food
intake and metabolic rate.
Ghrelin
is released from the stom-
ach during fasting. The details of these GI hormones will be
described in Chapter 16. Briefl
y, leptin induces satiety, while
ghrelin stimulates hunger.
In addition to their stimulation (or in some cases inhibi-
tion) of effector cell functions, the gastrointestinal hormones
Table 15–4
Properties of Gastrointestinal Hormones
Gastrin
CCK
Secretin
GIP
Chemical class
Peptide
Peptide
Peptide
Peptide
Site of production
Antrum of stomach
Small intestine
Small intestine
Small intestine
Stimuli for hormone
release
Amino acids, peptides in
stomach; parasympathetic
nerves
Amino acids, fatty acids in
small intestine
Acid in small intestine
Glucose, fat in
small intestine
Factors inhibiting
hormone release
Acid in stomach;
somatostatin
Target Organ Responses
Stomach
Acid secretion
Motility
Growth
Stimulates
Stimulates
Stimulates
Inhibits
Inhibits
Inhibits
Inhibits
Pancreas
Bicarbonate secretion
Enzyme secretion
Insulin secretion
Growth of exocrine
pancreas
Stimulates
Potentiates secretin’s actions
Stimulates
Stimulates
Stimulates
Potentiates CCK’s actions
Stimulates
Stimulates
Liver (bile ducts)
Bicarbonate secretion
Potentiates secretin’s actions
Stimulates
Gallbladder
Contraction
Stimulates
Sphincter of Oddi
Relaxes
Small intestine
Motility
Growth
Stimulates ileum
Stimulates
Large intestine
Stimulates mass movement
Table 15–4
physiological
inquiry
Gastrinomas are tumors of the GI tract that secrete gastrin, leading to very high plasma concentrations. What might be some of the effects
of a gastrinoma?
Answer can be found at end of chapter.
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