868
UNIT 4
Maintenance of the Body
23
Table 23.1
Hormones and Paracrines That Act in Digestion*
HORMONE
SITE OF
PRODUCTION
STIMULUS FOR
PRODUCTION
TARGET ORGAN
ACTIVITY
Cholecystokinin (CCK)
Duodenal
mucosa
Fatty chyme (also partially
digested proteins)
Stomach
Liver/pancreas
Pancreas
Gallbladder
Hepatopancreatic
sphincter
Inhibits stomach’s secretory activity
Potentiates secretin’s actions on these
organs
Increases output of enzyme-rich pancreatic
juice
Stimulates organ to contract and expel
stored bile
Relaxes sphincter to allow entry of bile and
pancreatic juice into duodenum
Gastric inhibitory
peptide (GIP) (or
glucose-dependent
insulinotropic peptide)
Duodenal
mucosa
Fatty chyme
Stomach
Pancreas (beta
cells)
Inhibits HCl production (minor effect)
Stimulates insulin release
Gastrin
Stomach
mucosa
(G cells)
Food (particularly
partially digested
proteins) in stomach
(chemical stimulation);
acetylcholine released by
nerve fibers
Stomach (parietal
cells)
Small intestine
Ileocecal valve
Large intestine
Increases HCl secretion
Stimulates gastric emptying (minor effect)
Stimulates contraction of intestinal muscle
Relaxes ileocecal valve
Stimulates mass movements
Histamine
Stomach
mucosa
Food in stomach
Stomach
Activates parietal cells to release HCl
Intestinal gastrin
Duodenal
mucosa
Acidic and partially
digested foods in
duodenum
Stomach
Stimulates gastric glands and motility
Motilin
Duodenal
mucosa
Fasting; periodic release
every 1½-2 hours by
neural stimuli
Proximal
duodenum
Stimulates migrating motor complex
Secretin
Duodenal
mucosa
Acidic chyme (also
partially digested proteins
and fats)
Stomach
Pancreas
Liver
Inhibits gastric gland secretion and gastric
motility during gastric phase of secretion
Increases output of pancreatic juice rich in
bicarbonate ions; potentiates CCK’s action
Increases bile output
Serotonin
Stomach
mucosa
Food in stomach
Stomach
Causes contraction of stomach muscle
Somatostatin
Stomach
mucosa;
duodenal
mucosa
Food in stomach;
stimulation by
sympathetic nerve fibers
Stomach
Pancreas
Small intestine
Gallbladder and
liver
Inhibits gastric secretion of all products
Inhibits secretion
Inhibits GI blood flow; thus inhibits
intestinal absorption
Inhibits contraction and bile release
Vasoactive intestinal
peptide (VIP)
Enteric
neurons
Chyme containing
partially digested foods
Small intestine
Pancreas
Stomach
Stimulates buffer secretion
Dilates intestinal capillaries
Relaxes intestinal smooth muscle
Increases secretion
Inhibits acid secretion
*Except for somatostatin, all of these polypeptides also stimulate the growth (particularly of the mucosa) of the organs they affect.
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