Final answer:
The organs located in the retroperitoneal space of the abdomen are the kidneys, which are well-protected and vascularized, receiving a significant portion of cardiac output.
Step-by-step explanation:
The question asks about which organs or structures are located in the retroperitoneal space of the abdomen. The retroperitoneal space is the area of the abdomen that lies between the parietal peritoneum and the posterior abdominal wall.
Among the options provided, the kidneys are the organs that are located in this space. The kidneys are situated on either side of the spine and are well protected by muscle, fat, and ribs. They are well vascularized, with each kidney receiving about 25 percent of the cardiac output at rest. The spleen, liver, and superior vena cava are not located in the retroperitoneal space.