Final answer:
In an IVU exam when the table is tilted into a Trendelenburg position, the ureters are the portion of the kidneys that are best demonstrated. This position uses gravity to enhance the visualization of the ureters as they fill with contrast.
Step-by-step explanation:
During an intravenous urography (IVU) exam, when the table is tilted to bring the patient into a Trendelenburg position, the portion of the kidneys that will be best demonstrated is the ureter. Tilting the table in this manner aids in visualizing the drainage system of the kidneys as it utilizes gravity to fill the ureters with contrast material, enhancing their visibility. The Trendelenburg position is characterized by having the body supine on the table with the feet elevated higher than the head. This position affects the spread of intravenous contrast in the urinary system and can provide an improved view of the ureters as they convey urine from the kidneys to the bladder. The anatomical structure of the retroperitoneal kidneys with the renal pelvis tapering into the ureter and their relationship with the bladder underscores the importance of positioning during the IVU to visualize potential issues like vesicoureteral reflux.