Functions of Cholecystokinin (CCK) in the Digestive System
Cholecystokinin (CCK) stimulates pancreatic enzyme secretion, causes relaxation of the sphincter of Oddi, and inhibits gastric emptying, but is not secreted by the antral mucosa. 1
Primary Functions of CCK
CCK is a 33 amino acid polypeptide hormone produced endogenously in the proximal small bowel (not the antral mucosa) and released into the bloodstream after ingestion of a meal, particularly in response to fat and protein 1, 2
CCK binds to receptors in the gallbladder causing contraction, while simultaneously binding to receptors on inhibitory neurons innervating the sphincter of Oddi causing relaxation, which leads to increased bile flow into the intestine 1
CCK is the principal hormone controlling gallbladder emptying in the postprandial state through this coordinated mechanism 1
CCK stimulates pancreatic enzyme secretion, which is essential for the digestive process 2, 3
Additional Physiological Effects of CCK
CCK inhibits gastric emptying, which optimizes the ratio of food and digestive secretions in the small intestine 1, 4
CCK acts as a satiety signal to the brain, limiting food intake and suppressing appetite 1, 2
CCK increases intestinal peristalsis, which can be responsible for abdominal cramping when administered rapidly intravenously 1
CCK Beyond Digestive Functions
CCK functions not only as a hormone but also as a neurotransmitter in central and peripheral neurons 3, 5
CCK is considered the most abundant neuropeptide in the human brain 3
CCK may play roles as a paracrine growth factor, anti-inflammatory cytokine, incretin, adipokin, and myokine 5
Regulation of CCK Secretion
CCK-releasing factors (CCK-RF) are secreted tonically by the small intestine and stimulate CCK release 2, 6
"Monitor peptide," a type of CCK-RF, is produced by pancreatic acinar cells and secreted via the pancreatic duct into the duodenum where it stimulates CCK secretion 6
Bile exclusion from the duodenum causes an increase in basal CCK levels, while bile salt replacement reverses these effects, suggesting CCK-producing cells are under constant suppression by intraduodenal bile acids 2
Clinical Implications
CCK-cholescintigraphy (CCK-CS) has become a standard clinical practice for assessing gallbladder function by measuring gallbladder ejection fraction (GBEF) 1
Abnormal gallbladder emptying may be associated with functional gallbladder disorder (FGBD) and biliary pain 1
Plasma CCK levels may be elevated in certain conditions like gallstone pancreatitis, potentially aggravating the condition by stimulating the injured pancreas 2
CCK has diagnostic applications in gallbladder and pancreatic diseases, as well as in medullary thyroid carcinomas 3