The kidneys are two bean-shaped organs that play an essential role in maintaining overall health. Located on either side of the spine, just below the rib cage, they continuously filter the blood to remove waste products and excess fluid. However, their functions go beyond urine production. The kidneys help regulate blood pressure, maintain the balance of electrolytes, control the body’s acid levels, and support red blood cell production. They also contribute to bone health by helping regulate calcium and phosphorus levels. These functions work together to keep the body functioning properly.
Understanding the 7 functions of the kidneys highlights why kidney health is important and how early detection of kidney problems can support timely medical care and better health outcomes.
What Are the Kidneys?
You have two kidneys, each roughly the size of your fist, sitting on either side of the spine just below the rib cage. Inside each one are about a million tiny filters called nephrons. Blood flows through them all day and all night, and a large share of the blood your heart pumps passes through the kidneys every minute.
Together, the kidneys filter around 180 litres of fluid a day. Most of it is taken back into the body. Only the waste and extra water leave as urine, usually about one to two litres. The urine travels down two thin tubes called ureters into the bladder, where it’s stored until you pass it through the urethra. These parts together make up the urinary system.
Function 1: Filtering Waste From the Blood
Your body produces waste every day. It comes from digesting food, using your muscles and breaking down medicines. Creatinine and urea are two common waste products that doctors measure in a blood test. The kidneys pull these out of the blood and send them out in urine, while keeping what the body needs, such as protein, glucose and most salts.
When filtering slows down, waste can build up. This is why doctors look at blood creatinine and the eGFR, an estimate of how well the kidneys are filtering, when they assess kidney health. A high creatinine doesn’t tell the whole story on its own, but it prompts a closer look.
Tiredness, nausea, poor appetite and a metallic taste can sometimes be linked to a build-up of waste. These symptoms have many other causes too, so they’re a reason for tests, not for assuming the worst.
Function 2: Balancing Body Fluids
Think of your kidneys as a thermostat for water. When you drink a lot, they let more water go. When you’re short of fluid, they hold on to it, and your urine becomes darker and lower in volume.
This balance keeps your blood volume steady and protects the heart and other organs. When the kidneys can’t manage it, fluid may collect in the body. You might notice swollen ankles, puffy eyes or a feeling of breathlessness. Too little fluid, on the other hand, can cause dizziness, dry mouth and very concentrated urine.
If you have a kidney, heart or liver condition, please follow your doctor’s advice on how much to drink. A general rule doesn’t suit everyone.
Function 3: Helping Control Blood Pressure
The kidneys help manage blood pressure in two ways. First, they control the amount of salt and water in the body, which affects the volume of blood in your vessels. Second, they release a hormone called renin, which starts a chain of signals known as the renin-angiotensin system. This system tightens or relaxes blood vessels as needed.
The link works in both directions. Long-standing high blood pressure can damage the small vessels inside the kidneys, and damaged kidneys can make blood pressure harder to control. That’s why people with high blood pressure are usually advised to have kidney tests, and people with kidney disease need regular blood pressure checks.
High blood pressure often causes no symptoms. A simple reading at home or in a clinic is the only dependable way to know where you stand.
Function 4: Making Red Blood Cells
Specialised cells in the kidneys sense how much oxygen the blood is carrying. When the level drops, they release a hormone called erythropoietin, or EPO. It signals the bone marrow to make more red blood cells, which carry oxygen to every part of the body.
When kidney function falls significantly, EPO production can decrease, and anaemia may follow. People may feel tired and weak, get short of breath easily or look pale. Anaemia has many causes, including low iron and vitamin deficiencies, so a blood test is needed to understand what’s behind it. If you have known kidney disease, please don’t start iron or other supplements on your own.
Function 5: Balancing Minerals and Electrolytes
Sodium, potassium, calcium, phosphorus and magnesium are minerals dissolved in your blood. Your nerves, muscles and heart depend on them staying in the right range. The kidneys adjust how much of each one is kept and how much is passed out in urine.
Potassium deserves a special mention. If it goes too high or too low, it can affect the heart’s rhythm. In advanced kidney disease, potassium can rise, which is why doctors monitor it with blood tests.
Mineral imbalances may show up as muscle cramps, weakness, palpitations or confusion. Only a blood test can confirm them. Any advice on limiting potassium or phosphorus in your diet should come from your doctor or a dietitian, based on your own reports.
Function 6: Supporting Bone Health
The vitamin D that comes from sunlight and food isn’t active when it enters the body. The kidneys convert it into its active form, which helps the intestine absorb calcium. They also help control phosphorus levels. Together, these actions keep bones and teeth strong.
In long-standing kidney disease, this process can be disturbed. Calcium, phosphorus and parathyroid hormone levels may change, and over time the bones may become weaker. Doctors call this group of changes CKD-mineral and bone disorder. It usually develops slowly, and routine blood tests often pick up the changes before any symptoms appear. When symptoms do occur, they can include bone pain, muscle weakness or fractures after minor injuries.
Function 7: Removing Extra Acid
Normal metabolism produces acids every day, and the body needs its blood to stay within a narrow pH range. The lungs help by breathing out carbon dioxide. The kidneys help by removing acid in the urine and by managing bicarbonate, a natural buffer in the blood.
When the kidneys can’t keep up, acid can build up. This is called metabolic acidosis. It may cause tiredness, faster breathing, nausea or weakness, and over time it can affect bones and muscles. A blood test detects it, and treatment depends on the cause and on the person’s reports.
Signs Your Kidneys May Need Attention
Kidney problems can develop gradually without causing noticeable symptoms in the early stages. As kidney function changes, some people may experience symptoms that require medical assessment. Recognising these signs can help people seek appropriate care.
Possible signs include:
- Swelling in the feet, ankles, legs, or around the eyes
- Foamy urine, which may be associated with protein in the urine
- Changes in urination frequency, particularly during the night
- Blood in the urine
- Persistent tiredness or weakness
- Nausea or reduced appetite
- Pain in the back or sides
These symptoms do not necessarily indicate kidney disease. They can occur due to several other conditions, including urinary tract infections, kidney stones, and other health problems. A qualified doctor can assess the symptoms and recommend suitable investigations, such as blood and urine tests.
It is also important to understand that the absence of symptoms does not rule out kidney disease. People with diabetes, high blood pressure, or other risk factors may benefit from regular kidney function assessments recommended by their healthcare professional.
Common Causes and Risk Factors for Kidney Damage
Kidney damage can occur due to several medical conditions, inherited factors, and lifestyle-related risks. Identifying these factors can help guide appropriate screening and management.
Diabetes
Diabetes is a common cause of chronic kidney disease. Persistently high blood glucose levels can damage the small blood vessels and filtering structures in the kidneys. Over time, this may affect their ability to remove waste products and excess fluid from the blood.
Managing blood glucose levels and attending recommended medical reviews can help monitor kidney health.
High Blood Pressure
High blood pressure can damage the blood vessels in the kidneys, reducing their ability to function effectively. Kidney disease can also contribute to high blood pressure, creating a cycle in which each condition may worsen the other.
Regular blood pressure monitoring and following a prescribed treatment plan are important for people with either condition.
Smoking and Obesity
Smoking can affect blood vessels and increase cardiovascular risk. Obesity is associated with conditions such as diabetes and high blood pressure, which may increase the risk of kidney disease. Maintaining a healthy weight and avoiding tobacco can support overall health.
Certain Medicines
Some medicines, including non-steroidal anti-inflammatory drugs (NSAIDs), may affect kidney function, particularly when used frequently or for long periods in susceptible individuals. The risk may be higher in people who already have kidney disease, dehydration, or certain other medical conditions.
Consult a qualified healthcare professional before using painkillers, herbal remedies, or supplements regularly. Do not stop prescribed medicines without medical advice.
Kidney Stones and Urinary Tract Problems
Kidney stones can cause pain, blood in the urine, or urinary obstruction. Repeated urinary tract infections and prolonged blockage of urine flow may also contribute to kidney damage in some circumstances. An enlarged prostate can obstruct urine flow in some men and may require medical assessment.
Family History and Autoimmune Conditions
Some kidney diseases have an inherited component. A family history of kidney disease may increase a person’s risk, depending on the condition.
Certain autoimmune disorders can cause inflammation in the kidneys. People with these conditions may need specific investigations and monitoring based on their medical history.
Although not every risk factor can be changed, appropriate screening and management of underlying conditions can help identify kidney problems and guide care.
Everyday Habits That Support Your Kidneys
There’s no magic food or drink for the kidneys. What helps is a steady routine:
- Drink water as your doctor advises, and don’t ignore thirst
- Keep an eye on salt, especially in packaged and fried foods
- Eat a balanced diet with vegetables, fruit and whole grains, unless your doctor has asked you to limit certain foods
- Stay physically active in a way that suits your health
- Keep blood pressure and blood sugar in check and take prescribed medicines regularly
- Check with a doctor before using painkillers, herbal products or supplements regularly
- Avoid smoking and limit alcohol
- Get a kidney check-up if you have diabetes, high blood pressure or a family history of kidney disease
Conclusion
Your kidneys do much more than produce urine. They filter waste products from the blood, regulate fluid and electrolyte balance, help control blood pressure, support red blood cell production, contribute to bone health, and maintain the body’s acid-base balance. These functions are essential for normal body processes.
Because kidney disease may develop without noticeable symptoms, understanding your risk factors and attending recommended health checks are important. Managing diabetes and high blood pressure, following appropriate lifestyle habits, and using medicines carefully can support overall kidney health.
Blood and urine tests can help assess kidney function and identify signs of damage. If you have concerns about your symptoms or test results, consult a qualified healthcare professional who can review your medical history and recommend appropriate care.
Read More: What Foods Cause Kidney Stones
