Cholecystokinin or CCK is a hormone produced by the digestive tract, mostly in the small intestine. It plays a role in the digestion of proteins and fats, and it also has an effect on the brain and vagus nerve, generating feelings of satiety which are designed to shut down the appetite once someone has eaten enough. In addition to being produced naturally by the body, this hormone is sometimes injected for the purpose of diagnostic tests.
One of the major actions of this hormone is on the gall bladder. In fact, the name “cholecystokinin” means “moving the gall bladder,” referencing the fact that this hormone causes the gallbladder to contract, stimulating it to release bile into the digestive tract. Cholecystokinin also stimulates the body to produce more bile, along with digestive enzymes. The digestive tract produces the hormones when fats are detected.
Studies seem to suggest that cholecystokinin may play a role in the development of drug dependence and tolerance, in addition to acting in the brain to produce feelings of anxiety and nausea. Like many hormones, cholecystokinin is very complicated, and it acts in a number of ways to produce its desired effect, which is the digestion of certain molecules and the suppression of appetite to prevent overeating.
Like other hormones related to feelings of satiety, cholecystokinin can take some time to act in the body. This is one of the reasons that people are encouraged to eat slowly, and to wait for 10-20 minutes if they still feel hungry after a meal. Often, the feeling of hunger resolves as the body's hormones start to act on the brain. Conversely, competitive eaters try to eat as much as possible as quickly as possible so that they can win competitions before the chemicals which induce satiety start acting on their brains, making it difficult or impossible to eat more food.
In diagnostic tests which are designed to assess whether or not the gallbladder is working properly, a doctor may inject cholecystokinin into a patient and monitor his or her response. This controlled introduction of cholecystokinin into the body allows a doctor to see if the gallbladder and digestive tract are working as they should be. If the gallbladder fails to respond, it can indicate that the patient has a problem and that further diagnostic tests may be needed. Before performing this test, a doctor will conduct a patient interview to make sure that it will be safe and suitable.