Nephritis is inflammation of the kidney. The word comes from the Greek nephro- meaning "of the kidney" and -itis meaning "inflammation". Nephritis is often caused by infections, toxins, and auto-immune diseases.
Nephritis is the most common cause of glomerular injury. It is a disturbance of the glomerular structure with inflammatory cell proliferation. This can lead to: reduced glomerular blood flow leading to reduced urine output (oliguria) & retention of waste products (uremia). As a result, there can also be leakage of red blood cells from damaged glomerulus (hematuria). Low renal blood flow activates the renin-angiotensin-aldosterone system (RAAS), which therefore causes fluid retention and mild hypertension.