The kidneys play a fundamental role in maintaining health. Humans typically have two kidneys, yet individuals can live a full and healthy life with only one. This raises a natural question: if one kidney is sufficient for survival, why do we commonly possess a pair? Understanding their functions, biological redundancy, and adaptability provides insight into this biological design.
The Kidney’s Role in Your Body
Kidneys are bean-shaped organs situated below the ribs towards the middle of the back. Their primary function involves filtering waste products from the blood, such as urea and creatinine, which are then excreted from the body as urine. Each minute, the kidneys filter about half a cup of blood.
Beyond waste removal, kidneys are also responsible for maintaining the body’s fluid and electrolyte balance, ensuring proper levels of substances like sodium and potassium. They play a role in regulating blood pressure by producing hormones such as renin. Kidneys also produce erythropoietin, a hormone that stimulates red blood cell production in the bone marrow, and help convert vitamin D into its active form, which is important for bone health.
Biological Redundancy: Why Two Kidneys Exist
Having two kidneys exemplifies biological redundancy, providing a built-in backup system and a margin of safety. If one kidney is compromised due to injury, disease, or donation, the other can continue essential tasks.
This reserve capacity ensures the body maintains optimal filtering and regulatory functions, even if one organ declines. It prevents immediate health crises and allows adaptation. While one kidney can sustain life, two provide a greater buffer against unforeseen challenges and support overall physiological efficiency.
How a Single Kidney Compensates
When one kidney is absent or removed, the remaining kidney undergoes physiological adaptations to compensate for the loss. One such adaptation is renal hypertrophy, where the single kidney increases in size and mass. This enlargement involves both the tubules and the filtering units called glomeruli.
Accompanying hypertrophy is hyperfiltration, a process where the remaining nephrons increase their workload and efficiency. This allows the single kidney to process a greater volume of blood and maintain the body’s waste removal and regulatory functions effectively. As a result, the overall glomerular filtration rate (GFR) of a single kidney can approach the levels normally achieved by two kidneys, often reaching up to 70-75% of the function of two healthy kidneys.
Life with One Kidney: Considerations and Care
Most individuals with a single kidney lead normal, healthy lives without significant long-term problems. This can be due to congenital absence, removal from disease or injury, or donation. Regular medical check-ups are recommended.
Monitoring kidney function through blood tests (eGFR) and urine tests (albuminuria) is important. Maintaining a healthy lifestyle, including a balanced diet, adequate hydration, and regular exercise, supports overall kidney health. Avoiding activities with a high risk of kidney injury, such as certain contact sports, is also advised, and protective gear may be considered.