Final answer:
Diabetic nephropathy and polycystic kidney disease are two significant causes of bilaterally enlarged, smooth kidneys, both leading to increased kidney size due to different pathological mechanisms.
Step-by-step explanation:
Two causes of bilateral large, smooth kidneys include various kidney diseases and disorders. One primary cause is linked to diabetic nephropathy, a condition that arises as a complication of diabetes, leading to chronic kidney damage. When the glomeruli in the kidneys are affected, this damage can manifest as increased kidney size.
A second major cause is polycystic kidney disease (PKD), a genetic disorder characterized by the growth of numerous cysts in the kidneys, causing them to enlarge. Both conditions lead to an increase in kidney size and are identified through medical imaging and clinical assessment.