Nephritis is inflammation of one or both kidneys. When the kidneys inflame, they begin to excrete needed protein from the body into the urine stream (proteinuria). Although nephritis can sometimes be caused by infection, it is most commonly caused by autoimmune disorders, such as lupus, which affects the major organs. For example, those with lupus are at a much higher risk for developing nephritis. It can also be genetically inherited, but it is rare. Nephritis is the ninth highest cause of human death.
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.
There are four types of nephritis: glomerulonephritis, interstitial nephritis, pyelonephritis, lupus nephritis. Nephritis causes the body to retain water, because the kidneys do not function properly to excrete the excess of water. Water retention can further cause swelling of the feet, ankles, legs, and hands.