2. 2-Stage of decompensation progressive urethral obstruction &presence of infection decompensation of the detrussor may occur result in high residual urine may reach up to 500 ml or more.

3. Pathogenesis &Pathology: Upper tract: 1- Ureter: -In early stage the intravesical pressure is not transmitted into the ureters because of the competence of the ureterotrigonal unit. -Later hypertrophy of trigone. -Vesicoureteral reflux. -Intravesical pressure transmitted to urete and pelvis. -Thickening and tourtiousity of the ureter.

7. 2-The kidney: - The pressure in the renal pelvis is zero. -Increase pressure due to obstruction or reflux lead to hydronephrosis> Stage of compensation: Stage of decompensation:

8. Effect of hydronephrosis on the kidney: 1- The early changes : The end of the normal calyx is concave with increase pressure it becomes convex(clubbed). Changes in the parenchyma are due to: a-Compression atrophy. b-Ischemic atrophy mainly manifested in arcuate vessels that run at the base of the pyramid.