KidneysEdit
The kidneys are a pair of bean-shaped organs tucked into the back of the abdominal cavity. They are central to maintaining the body’s internal balance by filtering the blood, removing waste, and regulating fluids and electrolytes. Each kidney contains roughly a million microscopic units called nephrons, which perform the essential work of cleansing the blood and shaping the composition of urine. Beyond filtration, the kidneys participate in hormone production that helps regulate blood pressure, red blood cell production, and mineral metabolism. In aggregate, this system supports overall health by sustaining a stable internal environment, which is a prerequisite for the proper functioning of every other organ.
A thorough understanding of the kidneys requires looking at their anatomy and physiology. The kidneys are supplied with blood by the renal arteries and are organized into outer cortex and inner medulla regions. Inside each nephron, the glomerulus acts as a filtering membrane where blood plasma is first filtered, while the tubules reabsorb needed substances and secrete waste products to form urine. The urine drains from the collecting ducts, passes into the renal pelvis, and moves down the ureter to the bladder. The kidneys’ daily workload is substantial: they filter a large volume of blood and produce urine as a primary path for waste elimination and chemical balance. The kidneys also contribute to blood pressure regulation through the renin-angiotensin-aldosterone system and synthesize hormones such as erythropoietin and calcitriol, which influence red blood cell production and calcium metabolism, respectively. For a broader view of the organs involved in waste removal, see Urinary system.
Anatomy and physiology
Functional units
The nephron is the fundamental unit of the kidney. Each nephron combines two processes: filtration of blood in the glomerulus and selective reabsorption and secretion along the tubule. The glomerulus sits within the renal corpuscle, and its filtration barrier determines what passes into the filtrate. The proximal tubule reabsorbs the majority of filtered water and solutes, the loop of Henle creates a concentration gradient, and the distal tubule and collecting duct adjust final urine composition under hormonal control.
Blood flow and regulation
The kidneys receive a significant portion of cardiac output, reflecting their importance in maintaining internal homeostasis. Blood is filtered through the glomerular capillaries, while the efferent and afferent arterioles help regulate filtration rate. Hormonal feedback, particularly via the renin-angiotensin-aldosterone system, adjusts kidney function in response to changes in blood pressure and volume.
Hormones and metabolic roles
Erythropoietin produced by the kidneys stimulates red blood cell production in the bone marrow. Calcitriol, the active form of vitamin d, helps regulate calcium and phosphate balance, supporting bone health and mineral metabolism. The kidneys also participate in acid-base balance by excreting hydrogen ions and reclaiming bicarbonate as needed.
Diseases and conditions
Chronic kidney disease and acute kidney injury
Chronic kidney disease (CKD) is the gradual loss of kidney function over time, commonly linked to diabetes and hypertension, though familial diseases and autoimmune conditions also contribute. Acute kidney injury (AKI) is a sudden decline in kidney function often triggered by dehydration, injury, or certain medications. Both CKD and AKI may progress to end-stage renal disease (ESRD) if kidney function becomes severely impaired.
Common disorders and risk factors
Nephrolithiasis (kidney stones) involves mineral deposits that can cause pain and urinary symptoms. Polycystic kidney disease features fluid-filled cysts that disrupt normal kidney architecture. Glomerulonephritis and nephrotic syndromes reflect inflammation or damage to the glomeruli and surrounding structures, altering filtration and protein loss.
Symptoms, diagnosis, and screening
Symptoms vary with the stage and underlying condition but may include swelling, fatigue, changes in urination, high blood pressure, and electrolyte disturbances. Blood tests, urine analysis, imaging, and kidney biopsy may be used to establish diagnosis and guide treatment.
Treatments and interventions
Dialysis
Dialysis serves as an artificial substitute for lost kidney function when the kidneys can no longer maintain homeostasis. Hemodialysis filters blood through a machine, typically several times per week, while peritoneal dialysis uses the peritoneal membrane to remove waste products through a cleansing fluid inserted into the abdomen. Dialysis improves quality of life and survival for many patients, though it is a demanding and ongoing modality.
Kidney transplantation
Transplantation offers a potentially curative option for ESRD, replacing failed kidneys with a donor organ. Success depends on matching compatibility, addressing immune suppression, and ongoing medical care to prevent rejection. Living donation and deceased donor programs shape the availability of donor kidneys, and policy frameworks govern allocation and access. See kidney transplantation and organ donation for broader context.
Pharmacology and supportive care
Across kidney disease management, medications such as antihypertensives and agents that control electrolyte balance may be used. In cases of anemia related to reduced erythropoietin production, therapies may support red blood cell counts. Diet, fluid management, and lifestyle adjustments complement medical treatments to slow progression and manage symptoms.
Health policy and economic considerations
Financing and access
In many systems, care for kidney disease spans private insurance, public programs, and out-of-pocket costs. In some countries, organ transplantation, dialysis, and related services are heavily funded by public programs to ensure access for those who need it most. Advocates for a more market-based approach emphasize consumer choice, competition among providers, and the potential for cost savings through efficiency, innovation, and price transparency. Critics warn that market-based reforms must be carefully designed to prevent inequities in access and to safeguard vulnerable patients.
The ESRD program and cost considerations
A longstanding policy in some jurisdictions provides coverage for end-stage renal disease treatment, reflecting the high cost and life-sustaining nature of dialysis and transplantation. Supporters argue that this coverage can save lives and reduce long-run costs by enabling timely treatment and transplantation. Critics worry about the sustainability of entitlements and about incentives that could influence the balance between dialysis and transplant options. The debate often centers on how to balance patient autonomy, provider innovation, and prudent stewardship of public funds.
Market structure and provider practice
The dialysis industry includes large private providers and independent clinics. Market competition can spur innovation in home dialysis technologies, patient education, and care coordination, but it also raises questions about profit motives, patient outcomes, and regulatory oversight. Discussions about price transparency, contracting with public payers, and quality accountability are common in this arena. See DaVita and Fresenius Medical Care for examples of private providers in the field.
Donor supply, ethics, and policy
Organ donation policies influence the availability of kidneys for transplantation. Debates include whether to use opt-in versus opt-out frameworks and whether there should be compensated donation under strict safeguards. Proponents of regulated incentive models argue that they could expand the donor pool while maintaining ethical protections; opponents raise concerns about exploitation and equity. See organ donation and APOL1 for related scientific and policy discussions.
Disparities and prevention
Differences in risk factors, incidence, and access to care can lead to uneven outcomes among different populations. Addressing these disparities often involves a mix of public health prevention (e.g., diabetes and hypertension management), access to early screening, and ensuring equitable referral pathways to specialist care. In some contexts, researchers examine how genetic predispositions, social determinants, and access to preventive services interact with kidney disease risk. See APOL1 and nephrology for related topics.