CCK-58 molecule contains 58 amino acids (CCK-58), CCK-39 contains 39 amino acids, CCK-12 contains 12 amino acids, and CCK-8 contains 8 amino acids. However in all types of CCK, 5 amino acids are located at the carboxyl terminal. A tretrapeptide CCK-4 is also present in various tissues. In the human body, only the sulfated form of CCK is present. CCK has a half-life of about 5 minutes. It is found in several other parts of the body such as the cerebral cortex, parts of the distal ileum and colon, etc.
As it is present in the CNS, it may stimulate appetite and consumption of food. It is also suggested to play an important role in the development of aggression and anxiety. Different types of CCK may be emitted from various parts of the body. CCK-8 is emitted from the junction of the duodenum and jejunum, whereas CCK-4 is emitted into the enteric and pancreatic nerves (Ganong, 2005). CCK is also produced in a pre-hormone form (similar to gastrin). It is united to form a family of peptides that have the same carboxyl (Bowen, 2001).
CCK affects the secretion of the pancreatic juice. CCK-PZ controls the delivery of digestive enzymes from the pancreas into the small intestine. It also controls the secretion and flow of the bile juice from the gall bladder. It helps to reduce the amount of gastric emptying and also stimulates release of enterokinases. It helps in the growth and development of the pancreas. CCK stimulates the movement of the small intestinal and colonic smooth muscles. It also stimulates the constriction of the pyrolic sphincter (an action brought along with secretin).
This helps to prevent the backward movement of the food from the duodenum, back into the stomach. CCK release is stimulated by a protein diet. Along with gastrin, CCK helps in the release of glucagon (Ganong, 2005 & Bowen, 2001). The receptors of CK present include CCK-A and CCK-B. CCK-A is usually present in the peripheral parts of the body, whereas CCK-B is usually present in the brain. To be more precise, CCK – A receptors are pinpointed in the acinar cells of the pancreas. The CCK-B receptors are present in the CNS, and a few are present in certain parts of the stomach.
CCK is increased in various conditions such as consumption of a protein diet, presence of fatty acids, presence of bile, and presence of pancreatic juice in the duodenum (Ganong, 2005 & Bowen, 2001). During the process of digestion, the complex substances of food including the proteins, polysacchrides and triglycerides should be digested into micro-molecules (scuh as fatty acids, amino acid and monosaccharides). The bile acids from the gall bladder and the digestive enzymes of the pancreas play a very important role in breaking down these complex food substances into simpler ones so that they could be absorbed by the body into the blood.