Dialysis is a medical treatment that filters a person’s blood, removing waste products and excess fluids when the kidneys are no longer able to function adequately. A common misconception is that dialysis directly removes urine from the bladder. However, dialysis does not interact with the bladder or remove any urine already present there.
The Kidney’s Role in Urine Production
The kidneys are a pair of organs located on either side of the spine, just below the rib cage. They are central to the body’s filtration system, continuously filtering blood to remove waste products and excess water to form urine. This process is essential for maintaining a chemical balance within the body. Each kidney contains millions of tiny filtering units called nephrons.
Blood enters the kidneys, and within these nephrons, water and small solutes are filtered out of the bloodstream. Most of this filtered fluid is reabsorbed back into the body, while the remaining waste products and excess water become urine. This urine then travels from the kidneys through tubes called ureters to the bladder for storage.
How Dialysis Works
Dialysis is a medical procedure that replicates the blood-filtering function of healthy kidneys when they are no longer able to perform adequately. It removes waste products, toxins, and excess fluid directly from the blood. This process occurs either outside the body using a machine, known as hemodialysis, or inside the abdominal cavity, called peritoneal dialysis.
In hemodialysis, blood is drawn from the body, typically from a vein in the arm, and circulated through an artificial kidney, or dialyzer. The dialyzer contains a semi-permeable membrane that allows waste products and excess fluid to pass from the blood into a special cleansing solution called dialysate, while clean blood is returned to the body. Peritoneal dialysis, conversely, uses the lining of the abdomen, called the peritoneum, as a natural filter. A cleansing solution is introduced into the abdominal cavity through a surgically placed catheter, where it absorbs waste and excess fluid from the blood vessels in the peritoneum before being drained out.
Dialysis and Remaining Kidney Function
The amount of urine a person on dialysis produces can vary significantly, depending on their residual kidney function. This refers to the remaining ability of their native kidneys to eliminate water and uremic toxins. Many patients starting dialysis still produce some urine, even if it is a reduced amount.
Preserving this residual kidney function is beneficial, contributing to better fluid control and improved patient outcomes. However, kidney function often declines further over time for individuals undergoing dialysis. Some patients may eventually produce very little or no urine at all. For those who produce little to no urine, fluid intake must be carefully managed and restricted to prevent fluid overload, which can lead to serious health complications.
The Bladder’s Function
The bladder is a hollow, muscular organ that serves primarily as a storage reservoir for urine. It is not involved in the production of urine; its role is to collect urine that travels from the kidneys via the ureters. The bladder expands as it fills, and nerves send signals to the brain when it reaches a certain capacity, creating the urge to urinate.
When a person urinates, the bladder muscles contract and sphincter muscles relax, allowing urine to exit the body through the urethra. Dialysis does not empty the bladder or directly influence its ability to store or release urine. If a person on dialysis still produces urine due to remaining kidney function, that urine will continue to follow the natural path to the bladder for storage and eventual voiding.