The document discusses two causes of obstructive uropathy: nephrolithiasis and hydronephrosis. Nephrolithiasis is the formation of urinary calculi (stones) in the kidneys or urinary tract. Calculi most commonly occur in middle-aged men and can cause pain. Hydronephrosis is the dilation of the renal pelvis and calyces due to partial or intermittent blockage of urine flow. It is usually caused by obstruction in the ureter but can also be congenital or due to conditions affecting the bladder. Advanced hydronephrosis leads to compression of the renal cortex. Both conditions are demonstrated in photographs showing enlarged kidneys with dilated pelvis and