Describe disorders related to the excretory system.

(A) - $Uremia$: Accumulation of urea in the blood is termed $Uremia$. It is highly harmful and may lead to kidney failure.
- $Renal$ $failure$: Malfunctioning of the kidneys,leading to improper excretion,is called renal failure. Causes include infections,injury to tubules,bacterial toxins,and adverse drug reactions.
- $Hemodialysis$: In patients with uremia,urea can be removed by a process called hemodialysis. $A$ hemodialyzer (artificial kidney) is used to filter blood.
- Blood is drained from a convenient artery,mixed with an anticoagulant like $heparin$,and pumped into the dialyzing unit.
- The unit contains a coiled cellophane tube surrounded by a dialyzing fluid with the same composition as plasma,except for nitrogenous wastes.
- The porous cellophane membrane allows the passage of molecules based on concentration gradients. Nitrogenous wastes move out into the fluid,clearing the blood.
- The purified blood is pumped back into the body through a vein after adding an anti-heparin.
- $Kidney$ $Stone$: Formation of insoluble masses of crystallized salts (e.g.,oxalates) within the kidney. These obstruct the urinary tract,causing acute back pain. When stones enter the urinary bladder,they cause severe pain. They can be removed surgically.
- $Nephritis$: Inflammation of the renal pelvis,interstitial tissues,and calyces,usually due to bacterial infection. Symptoms include a burning sensation during urination,back pain,and increased frequency of urination.