The type of cell junction that prevents the contents of the stomach or urinary bladder from leaking into surrounding tissues is called a tight junction.

Here's why:

* Tight junctions are specialized cell junctions that form a seal between cells, preventing the passage of fluids and molecules between them. They are like a zipper that runs along the entire length of the cell, creating a barrier.

* The stomach and urinary bladder contain very acidic or concentrated fluids that would be harmful to surrounding tissues if they leaked out. Tight junctions ensure that these fluids stay contained within the organ.

Other types of cell junctions, like desmosomes and gap junctions, have different functions and don't provide the same level of leak-proof barrier as tight junctions.