This is a hormone that is manufactured in the intestinal region, to be more specific in the jejunum and duodenum, by the action of I cells. In addition, it has the function of acting as an appetite depressant. In recent studies, data indicating that cholecystokinin may play an elementary role in stimulating opium-containing substances, such as heroin and morphine, in addition to being associated with hypersensitive pain experiences in patients with withdrawal syndrome due to the use of opiates.

This hormone is a polypeptide, which is secreted by the mucosal tissue of the small intestine, thanks to the stimulation exerted by the chyme, which is caused by the retraction of the gallbladder and the secretions of the pancreas. This hormone is also released in the hypothalamus where it functions as a neurotransmitter.

The main function of cholecystokinin is to secrete enzymes that originate in the pancreas and in bile, which are contained in the gallbladder and go to the duodenum, causing it to retract. , causing the channel that serves as a bridge between the common bile duct and the duodenum to relax and open. In addition to this, the hormone is also involved in the regulation of certain hormones regarding the digestion of food, where other hormones such as secretin and gastrin are also involved. The cells that are responsible for producing it are the so-called I cells, these are characteristic of the duodenum, so that these cells can start their production it is necessary that they be stimulated by the intervention of amino acids and fatty acids, all this will cause delay the emptying of the gastric content and the contraction of the gallbladder and that it empties the bile, which will initiate the absorption of fats. Subsequently, the chyme will pass through the duodenum and the stimulus will end.

The protein responsible for stimulating the intestine to produce its secretion is apelin, in addition to this it should be noted that the hormone cholecystokinin is also responsible for causing post-prandial drowsiness.