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Many diseases affect kidney function by attacking the glomeruli, the tiny units within the kidney where blood is cleaned. Glomerular diseases include many conditions with a variety of genetic and environmental causes, but they fall into two major categories:
- Glomerulonephritis (gloh-MEHR-yoo-loh-nef-RY-tis) describes the inflammation of the membrane tissue in the kidney that serves as a filter, separating wastes and extra fluid from the blood.
- Glomerulosclerosis (gloh-MEHR-yoo-loh-skleh-ROH-sis) describes the scarring or hardening of the tiny blood vessels within the kidney.
Although glomerulonephritis and glomerulosclerosis have different causes, they can both lead to kidney failure.
What are the kidneys and what do they do?
The two kidneys are bean-shaped organs located near the middle of the back, just below the rib cage to the left and right of the spine. Each about the size of a fist, these organs act as sophisticated filters for the body. They process about 200 quarts of blood a day to sift out about 2 quarts of waste products and extra water that eventually leave the body as urine.
Blood enters the kidneys through arteries that branch inside the kidneys into tiny clusters of looping blood vessels. Each cluster is called a glomerulus, which comes from the Greek word meaning filter. The plural form of the word isglomeruli. There are approximately 1 million glomeruli, or filters, in each kidney. The glomerulus is attached to the opening of a small fluid-collecting tube called a tubule. Blood is filtered in the glomerulus, and extra water and wastes pass into the tubule and become urine. Eventually, the urine drains from the kidneys into the bladder through larger tubes called ureters.
Each glomerulus-and-tubule unit is called a nephron. Each kidney is composed of about 1 million nephrons. In healthy nephrons, the glomerular membrane that separates the blood vessel from the tubule allows waste products and extra water to pass into the tubule while keeping blood cells and protein in the bloodstream.
How do glomerular diseases interfere with kidney function?
Glomerular diseases damage the glomeruli, letting protein and sometimes red blood cells leak into the urine. Sometimes a glomerular disease also interferes with the clearance of waste products by the kidney, so they begin to build up in the blood. Furthermore, loss of blood proteins like albumin in the urine can result in a fall in their level in the bloodstream. In normal blood, albumin acts like a sponge, drawing extra fluid from the body into the bloodstream, where it remains until the kidneys remove it. But when albumin leaks into the urine, the blood loses its capacity to absorb extra fluid from the body. Fluid can accumulate outside the circulatory system in the face, hands, feet, or ankles and cause swelling.