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What do the kidneys do?

Normally, each person is born with two kidneys, tucked under the rib cage in the back of the body on each side of the spine. The kidneys are about five-and-a-half inches long (14 cm), three inches wide (8 cm) and two inches thick (5 cm). They weigh 10 to 12 ounces.

Each kidney contains about 1 million tiny tubes called nephrons. A little over 22 percent of the blood the heart pumps every second goes to the kidneys. This blood flows through a filter, called a glomerulus, in the nephron. Red blood cells, white blood cells and large substances like protein don't normally pass through the glomerulus but rather stay in the body. The fluid that goes through the filter is made up of water, electrolytes and other small substances.

The kidneys are a regulating system. They make sure your electrolytes such as sodium, potassium, calcium, phosphorus and other chemicals are in balance. The kidneys also help regulate the pH of your body fluids so they are not too acidic or alkaline. The kidneys also filter and excrete waste products that your body produces each day.

Kidneys filter blood plasma and produce urine, whereby waste products are eliminated from the body. Without properly functioning kidneys, waste products build up in the blood causing a toxic condition known as uremic poisoning.

Blood urea nitrogen (BUN) and creatinine are two waste products that are removed by the kidney. In particular, creatinine is removed so efficiently that an estimate of kidney function can be made by the level of this substance in the blood. Your doctor can calculate approximately how much actual kidney function you have with a blood test for creatinine, a 24-hour urine collection, and your height and weight. This is called creatinine clearance, glomerular filtration rate or GFR.

Other functions of the kidney include making several essential hormones. One of these is renin, a hormone that in turn forms other hormones that help regulate blood pressure and the body's handling of salt.

Another hormone that is made in the kidneys is erythropoietin, commonly called EPO. EPO is a hormone that tells the bone marrow to make red blood cells. If a person's kidneys are surgically removed or if they fail because of a kidney disease, EPO is no longer produced and blood transfusions must be given to the person every five to seven weeks. The exact gene that codes for the protein erythropoietin was discovered several years ago. There is now a genetically manufactured form of EPO that a person can take, which eliminates the need for transfusions.

The kidneys also change vitamin D to its active form. In this way the kidneys help control calcium and bone formation. Because the kidneys perform all these functions, they are very important in keeping a person healthy.


What is PKD?

Polycystic Kidney Disease comes in two hereditary forms:

  1. Autosomal dominant (ADPKD), the most common of all life-threatening genetic diseases.
  2. Autosomal recessive (ARPKD), a relatively rare disease that often causes significant mortality in the first month of life.

A normal kidney is the size of a human fist. However, with the presence of PKD, cysts develop in both kidneys. There may be just a few cysts or many, and the cysts may range in size from a pinhead to the size of a grapefruit. When many cysts develop, the kidneys can grow to be the size of a football or larger and weigh as much as 38 pounds each.


What are cysts?

A cyst in the kidney begins as an outpouching of the nephron, similar to a blister. Cysts can occur anywhere on the length of the nephron. Although polycystic means many cysts, not every nephron forms cysts. The fluid inside the cysts often reflects the area in the nephron from which the cyst arose.

Approximately 70 percent of cysts detach from the nephron when they are still very small, about 2 mm (1/8 inch) in diameter. Over time the cysts enlarge and can become filled with clear fluid or fluid that contains blood or white blood cells.

Cysts can form in other organs as well as the kidney; the most common other site is the liver. Current research suggests that liver cysts are associated with the bile ducts or tubules of the liver rather than liver cells themselves. It appears that rather than take the place of functioning liver cells, cysts merely push the liver cells aside. This is why liver cysts don't cause liver failure even though the liver can become quite enlarged due to cysts.

Research has shown that there are at least three components to cyst formation:
  1. Cell proliferation: The cells of a cyst wall reproduce themselves more than do normal kidney cells. This makes the cysts grow in size.
  2. Cellular secretion: Secretion is a way of making fluid. To form a cyst the cells themselves must produce fluid. If there were no fluid produced to fill the cyst, there would merely be a ball of cells.
  3. Abnormal basement membrane: The basement membrane is a very thin layer of tissue the cyst cells sit on. In ADPKD this layer is thicker than usual and is made up incorrectly.

In general, cysts cause problems because of their size and the space they occupy. The size of the kidneys and liver is directly related to how many and how big the cysts are. For example, people with kidneys over 15 cm (6 inches) are more likely to have pain than people with smaller kidneys.



How come I've never heard of PKD before? Is it a new disease?

In the 1700s and 1800s, PKD was often given the label of Bright's disease. This term encompassed any of several kidney diseases marked by high concentrations of protein in the urine. Today, we know that many of the cases of Bright's disease were actually cases of PKD. The first documented case of PKD dates back to Stefan Bathory, the King of Poland, who lived from 1533 to 1588.

In addition, the PKD Foundation is the only organization in the world that focuses on PKD and it was not formed until the mid-1980s. It wasn't until fairly recently that PKD has gained some momentum in raising awareness and funds for the disease.

Another reason many have not heard of PKD is because it is an "internal disorder" ?meaning that it does not have a dramatic affect on a person's outward appearance. A person living with PKD may have pain or trauma on their internal organs, yet they maintain a very "normal" physical appearance that does not attract attention or compassion from the unknowing public.


If you would like more information on this please visit Or call 1-800-PKD-CURE!