Milk ultrasonography (MU) emerges as a valuable diagnostic tool for evaluating gallbladder function by assessing its emptying or refilling dynamics following oral administration of milk. Employing milk as a cholecystokinetic agent, MU enables cholecystodynamic studies with implications for understanding gastrointestinal hormone-mediated processes. Early experiments elucidated the hormonal-mediated contraction of the gallbladder upon food, particularly fat, entering the duodenum, accompanied by increased secretion of enzyme-rich pancreatic juice. Initially attributed to gastrointestinal hormones cholecystokinin (CCK) and pancreozymin, it was later revealed that a single hormone, CCK-pancreozymin (CCK-PZ), governed both actions, characterized by a 33 amino-acid sequence. Furthermore, the discovery of caerulein, a polypeptide with properties resembling both gastrin and CCK, extracted from the skin of Australian frogs, offers insights into novel approaches for inducing gallbladder contraction in humans. Notably, the vagus nerve plays a pivotal role in mediating motor signals to facilitate gallbladder contraction. This paper delves into the principles and applications of MU in cholecystodynamic assessment, shedding light on its utility in elucidating the complex interplay of gastrointestinal hormones and neural pathways governing gallbladder function. By synthesizing insights from experimental studies and clinical applications, it underscores the significance of MU in diagnosing gallbladder disorders and guiding therapeutic interventions.