Final answer:
The liver is the organ in the abdominal cavity that contains the largest store of blood, due to its extensive vascularization and crucial metabolic functions.
Step-by-step explanation:
The organ of the abdominal cavity that holds the largest store of blood in the body is the liver. The liver is the largest internal organ and it plays multiple roles, including a major role in metabolism and regulation. It stores a significant amount of blood due to its extensive vascularization and is involved in various metabolic processes such as gluconeogenesis, glycogenolysis, glycogenesis, and the breakdown of hormones. In contrast, the spleen, which is also highly vascularized, is involved in filtering the blood and immune system responses, but it does not hold the largest blood store.