So, how do the kidneys work?

Healthy kidneys are capable of filtering about 180 litres of fluid every day, removing waste and toxins from the plasma to make urine. Part of the urinary system, kidneys are the major excretory organ of the human body. The bladder stores this urine until it is excreted out through the urethra.

Why are the kidneys important?

The kidneys perform critical functions that are necessary to regulate and maintain the balance of body chemicals. These vital organs perform the following functions:

• Remove waste, toxins, and excess fluid from the body, a process that involves complex steps of filtration, reabsorption, secretion, and excretion.

• Remove acids produced by body cells and maintain a steady balance of salts, water, and minerals such as sodium, potassium, calcium, and phosphorus. Without this optimum balance, tissues such as nerves and muscles may not work correctly.

• Filter medication and drugs from the body.

• Release hormones that help control blood pressure.

• Produce the hormone EPO that controls the production of red blood cells.

• Promote strong and healthy bones by producing an active form of vitamin D.

How do the kidneys filter blood?

The kidneys filter blood in the following steps:

1. Blood flows to the kidneys: Blood flows from the aorta (the main artery branching from the heart) to the kidneys through the renal arteries. The renal arteries carry a large volume of blood, nearly 25% of the cardiac output, to the kidneys for filtration.

2. The two-step process of nephrons: The main functional and filtering units of the kidneys are the nephrons (each kidney has ~1 million nephrons). A nephron in turn consists of a filtering unit of tiny blood vessels called the glomerulus that is attached to a tubule that runs along the blood vessel. The nephrons work in a two-step process: the glomerulus filters the blood and the required chemicals are returned to the filtrate in the tubules.

3. Filtration of blood by the glomerulus: The walls of the glomerulus are fenestrated—the perforated and thin walls of the glomerulus allow small molecules (mostly minerals), fluids (mostly water), and wastes to pass into the tubule. Proteins and blood cells, which are larger, remain in the blood vessel.

4. Reabsorption in the tubule: The tubule runs along the blood vessel. As the filtrate (filtered blood) flows in the tubule, most of the water and essential nutrients and minerals such as glucose, salts, and amino acids are reabsorbed into the blood vessel. The newly filtered blood is recirculated into the body through the renal vein.

5. Removal of waste and transport of urine to the bladder: The tubule also helps remove the excess acid from the blood. The remaining fluid and wastes from the tubule, high in urea, become urine and are transported to the bladder for excretion.

What are the causes of kidney problems?

The following are the common causes of kidney damage:

• Diabetes: The leading cause of kidney disease is diabetes. Insulin is required to maintain proper sugar levels in the body. Diabetes is a condition where the body’s ability to produce or use insulin is impaired. When the sugar level in the blood is high, kidney function can get severely affected.

• High blood pressure (hypertension): Sustained high blood pressure can cause damage to the blood vessels and filters (glomeruli) in the kidneys and in advanced stages, renal failure.

• Kidney stones: Kidney stones are formed by the concentration of crystals in the urine. Stones can be formed due to many reasons, such as habits, diet, or an inherited tendency. They can cause severe pain in the sides and lower back when they pass.

• Urinary tract infections (UTI): Urinary tract infections (UTI) usually occur in the lower urinary tract—the bladder or the urethra. However, sometimes a UTI can spread to the upper urinary tract and infect the kidneys. This can prove to be dangerous as the infection can spread from the kidneys into the blood.

• Drugs and toxins: Sustained and frequent use of over-the-counter pain medication like NSAIDs (nonsteroidal anti-inflammatory drugs) can be harmful to kidneys. Toxins, pesticides, certain medications, and illegal drugs like heroin can also cause kidney damage.

• Inherited and congenital kidney disorders: Congenial conditions that develop in the womb that may result in defects that can cause improper kidney function, such as reflux or backing up of urine to the kidneys. Inherited kidney diseases such as polycystic kidney disease can cause serious kidney damage or even kidney failure.

What are the warning signs of kidney problems?

Kidney disease usually manifests in both kidneys. If the kidneys’ ability to filter blood is compromised, there may be a buildup of wastes, excess liquid, and toxins in the body, leading to serious complications. The warning signs of kidney disease are:

• Blood in the urine, or foamy urine.

• Hypertension, or high blood pressure.

• Cramping muscles.

• Swelling in hands and feet.

• Puffiness around the eyes.

• Difficulty or pain during urination.

• An increased frequency in urination, especially at night.

• A glomerular filtration rate lower than 60.

• Excess of Blood Urea Nitrogen (BUN) and creatinine in the blood.

Kidneys perform a vital role in maintaining the overall health of the body. Kidneys act as the blood filtration unit of the body and help maintain the right balance of body minerals. Knowing the importance of the renal system and understanding how kidneys function can help you keep your kidneys healthy and prevent future issues. This knowledge can be especially useful for understanding a treatment process when under the supervision of a urologist. For further information on kidney health, or to seek guidance regarding any kidney-related issues that you think you might have, reach out to the experts at the Department of Urology and Nephrology at Sagar Hospitals.