Fred, a fit and healthy 44-year-old, was working outside one warm summer afternoon. When he returned home by the end of the day, his lower back felt sore and he felt nauseated. His wife made him din

Fred, a fit and healthy 44-year-old, was working outside one warm summer afternoon. When he returned home by the end of the day, his lower back felt sore and he felt nauseated. His wife made him dinner, but he was not hungry and chose to go to bed instead. Fred’s symptoms progressed, and soon he was rolling on the bed with excruciating pain. He said his back hurt as well as his stomach and groin area. The pain would ease off only to return a short while later, and when it did, Fred would begin to sweat and run to the bathroom to vomit. His wife became concerned and started the car. When his symptoms abated, she helped him into the car and rushed him to the hospital.1. At the hospital, an abdominal radiograph showed the presence of renal calculi in Fred’s right ureter (urolithiasis). What is the mechanism of stone formation in the kidney? What is the role of citrate in the kidneys?2. Why would the administration of calcium supplements be useful for a patient with calcium oxalate stones?3. Hydronephrosis can be a complication of renal calculi. What is hydronephrosis? How does back pressure occur in a kidney, and what physiologic mechanism is responsible for nephron damage when back pressure is present?