Which of the following statements regarding the kidneys is correct?

• A. The kidneys eliminate toxic waste products from the body and control the body's fluid balance
• B. Both kidneys are located in the anterior abdominal cavity and lie in between the liver and spleen
• C. Because the kidneys require little oxygen, only 5% of the body's blood volume passes through them each minute
• D. A series of small blood vessels attach the kidneys directly to the superior vena cava and renal arteries

Answer: (A)

The correct statement is that the kidneys eliminate toxic waste products from the body and control the body's fluid balance. The kidneys function primarily to filter blood, removing waste products such as urea and creatinine that are produced from metabolism. They also play a crucial role in regulating fluid balance by adjusting the amount of water reabsorbed into the bloodstream or excreted as urine. Additionally, the kidneys help regulate electrolytes and maintain acid-base balance, all of which are essential for proper homeostasis in the body.

The other statements do not accurately represent the anatomical and physiological roles of the kidneys. For instance, the kidneys are positioned retroperitoneally in the abdominal cavity, rather than in the anterior abdominal cavity between the liver and spleen. The kidneys require a substantial blood supply, with approximately 20-25% of the cardiac output circulating through them, much more than the 5% suggested. Furthermore, while the renal arteries supply blood to the kidneys, they do not connect directly to the superior vena cava; instead, the superior vena cava receives deoxygenated blood from the body, while the kidneys filter blood that comes from the aorta through the renal arteries.