Final answer:
Total Parenteral Nutrition (TPN) causes gallbladder stones due to diminished gallbladder contractility, which can lead to bile stagnation and cholesterol crystallization, forming gallstones.
Step-by-step explanation:
Mechanism of TPN Causing Gallbladder Stones
The mechanism by which Total Parenteral Nutrition (TPN) causes gallbladder stones is most likely related to diminished gallbladder contractility. TPN can suppress the body's natural release of cholecystokinin (CCK), a hormone that controls the contraction of the gallbladder and the secretion of pancreatic enzymes. As a result of this suppression, the gallbladder does not contract as often as it should, which can cause bile to become stagnant and concentrate, leading to the formation of gallstones. Cholecystokinin normally stimulates the gallbladder to contract and release bile into the duodenum to aid in the digestion of fats. However, when the gallbladder's contractility is reduced, bile remains in the gallbladder for longer periods, increasing the likelihood of cholesterol crystallizing and forming gallstones.
Gallstones can lead to complications such as pain and jaundice if they obstruct the bile duct, preventing bile from being excreted, causing bilirubin to accumulate in the blood. The presence of gallstones in the bile duct is illustrated in Figure 6.7.7, where the blockage can lead to symptoms like pain and jaundice. TPN can inadvertently contribute to the risk of gallstone formation by affecting the normal physiological responses related to bile secretion and gallbladder function.