Cholecystokinin: Function & Diseases

Cholecystokinin (obsolete: pancreocymin, or CCK for short) is a hormone found mainly in the gastrointestinal tract. Translated into German, cholecystokinin means “gallbladder accelerator”. The name itself thus indicates that cholecystokinin plays a significant role in human digestion.

What is cholecystokinin?

Schematic diagram showing the anatomy and structure of the endocrine (hormone) system. Click to enlarge. CCK is a hormone that plays an essential role in digestion in the human body. The release of the hormone is stimulated by fatty and amino acids contained in food. The site of CCK production is the duodenum and the jejunum. CCK triggers a physiological feeling of satiety. It is also responsible for the formation of the secretion from the pancreas necessary for the decomposition of the food pulp. Contraction of the gallbladder – also indispensable for digestion – is also triggered by CCK.

Production, manufacture, and formation

CCK is produced in the duodenum and the jejunum. As soon as food passes from the stomach into the duodenum – the duodenum is the first section of the small intestine that directly adjoins the stomach and is closed by the gastric pylorus – the latter begins to “examine” the food pulp. Provided that fatty acids with a length of at least 12 carbon atoms are present, the duodenum begins to produce CCK. This secretion initially inhibits further emptying of gastric contents into the duodenum. CCK also stimulates the endocrine cells – cells that produce and release enzymes to the outside – of the pancreas to produce digestive enzymes. The pancreas releases the digestive enzymes into the duodenum, where they begin to break down proteins, carbohydrates and fats. Following the initial decomposition of food in the duodenum, the food is transported further towards the jejunum. The jejunum is immediately adjacent to the duodenum and flows into the ileum. In the jejunum, CCK is formed, which triggers contraction of the gallbladder. In the gallbladder, the human body stores bile produced by the liver, a secretion needed by the intestine for the digestion of fats. The contraction of the gallbladder triggered by CCK releases the secretion.

Function, action, and properties

CCK is essentially required for human digestion. As soon as it enters the duodenum, it initially inhibits the release of further food into the intestine. At the appropriate filling level, it signals a feeling of satiety to the human brain. Only when the first portion has left the duodenum can new food pulp flow in. The CCK also causes the pancreas to start producing digestive enzymes. The pancreas releases the secretion formed into the duodenum, where the enzymes begin to break down the food. The food then passes through the jejunum. CCK is also formed there and triggers contraction of the gallbladder. The bile stored there is also needed to break down food – especially long-chain fats. CCK thus plays a central role in the absorption and utilization of food. Through its satiety-triggering effect, it also regulates food intake in terms of quantity.

Diseases, ailments, and disorders

CCK plays a central role in the absorption and processing of food. Unless the secretion of CCK occurs in the required balance, humans complain of various ailments. Even food intake can be problematic when there is an undersupply of CCK, such as when the brain is not given an adequate feeling of satiety. In this case, people eat too much and complain of a lack of “now it’s enough” feeling. Depending on the severity of the deficiency, obesity can result. The link between CCK deficiency and obesity has been demonstrated in several animal studies. A connection between CCK deficiency and bulimia (binge eating disorder) is also suspected. Triggered by CCK deficiency, bulimics suffer from massive food cravings that they cannot control. The subsequent feeling of fullness in the stomach forces vomiting.CCK deficiency can cause an unpleasant feeling of fullness even with a normal diet, which can only be remedied by vomiting. A deficiency of CCK can also result in the release of food into the duodenum not being controlled evenly. Absorbed food remains in the stomach too long and flows back into the esophagus. Heartburn is the unpleasant and dangerous consequence of CCK deficiency. If not enough enzymes are released from the pancreas and gallbladder due to insufficient CCK secretion, the human body is unable to decompose food adequately. It has been observed that ingested energy is reduced by up to 9% in cases of pronounced CCK deficiency.