The kidney is a bodily organ that filters waste materials from the blood to produce urine, which is then eliminated from the body. Additionally, it regulates electrolyte levels, blood pressure, and the production of red blood cells.
The typical size of a human kidney is roughly around 10-12 centimeters or about 4-5 inches in length and 5-7 centimeters or about 2-3 inches) in width. Usually, humans have two kidneys, one on each side of the spine.
While humans usually possess two kidneys, one can survive with just one kidney. This condition is known as living with a solitary kidney. Many people are born with a single kidney, while others may undergo surgical removal of one kidney due to medical reasons such as kidney donation or disease.
Despite having only one kidney, most individuals can lead normal, healthy lives. The remaining kidney often compensates for the loss by increasing in size and function. However, it's essential to maintain good kidney health through a balanced diet, regular exercise, and avoiding factors that can harm kidney function
What are the parts of the kidney?
The kidney is an intricate organ consisting of numerous distinct components, each with its own function. These parts include:
- Nephrons : They are the kidney's structural components tasked with filtering blood and producing urine. Each kidney contains millions of nephrons, consisting of a renal corpuscle (glomerulus and Bowman's capsule) and renal tubules (proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct).
- Renal Cortex : The outermost part of the kidney, comprising structures like renal corpuscles (glomeruli) and renal tubules. The renal cortex is primarily involved in filtration and initial processing of blood.
- Renal Corpuscle : The renal corpuscle is a specialized structure within the kidney responsible for the initial filtration of blood to form urine.
The glomerulus consists of a collection of tiny blood vessels that take in protein from the blood as it moves through the renal corpuscle. Following this process, the remaining fluid, known as capsular urine, flows through the Bowman capsule and into the renal tubules.
- Renal Medulla : The inner part of the kidney, consisting of renal pyramids and renal columns. The renal medulla plays a role in concentrating urine and transporting urine toward the renal pelvis.
Triangular-shaped structures within the renal medulla, composed of collecting ducts and loops of Henle are called renal pyramids. The renal pyramids are responsible for transporting urine from the nephrons to the renal pelvis.
The collecting ducts, located at the terminus of each nephron in the renal medulla, serve as the exit point for filtered fluids. After entering the collecting duct, the fluid proceeds to its final destination in the renal pelvis.
- Renal Pelvis : A funnel-shaped structure located at the center of the kidney, where urine collects before it is transported to the ureter. The renal pelvis receives urine from the renal tubules and funnels it into the ureter.
- Perirenal Fat : Adipose tissue surrounding the kidney, providing cushioning and insulation
- Renal Columns : Extensions of cortical tissue that project into the renal medulla between the renal pyramids. Renal columns provide support and contain blood vessels and tubules.
- Renal Hilum : A concave region on the medial side of the kidney where the renal artery, renal vein, and ureter enter and exit the kidney.
- Renal Artery and Vein : Blood vessels that supply and drain blood from the kidney. The renal artery delivers oxygenated blood to the kidney for filtration, while the renal vein carries deoxygenated blood away from the kidney.
- Renal Capsule : A fibrous, protective covering surrounding the kidney, providing support and protection against injury.
- Ureter : Urine exits the kidney through a tube called the ureter, which leads to the bladder.
These parts work together to maintain proper kidney function, including filtration of waste products from the blood, regulation of fluid and electrolyte balance, and production of urine. Dysfunction of any of these parts can lead to kidney disorders and impaired renal function.
What functions do the kidneys perform?
The kidneys are vital organs with multiple functions critical for maintaining overall health. Some of the key functions of kidneys include:
- Regulation of Fluid Balance: Water is vital, but too much can be detrimental. The kidneys maintain the balance of body fluids by modulating the excretion of water and electrolytes, such as chloride, potassium and sodium, in urine, thereby regulating their volume and composition.This helps maintain proper hydration and electrolyte balance.
- Filtration of Waste Products: The kidneys filter waste products, toxins, and excess substances, such as urea, creatinine, and electrolytes, from the blood to form urine. This process helps maintain a proper balance of substances in the body.
- Blood Pressure Regulation: The kidneys are instrumental in controlling blood pressure by managing blood volume and the narrowing or widening of blood vessels through the renin- angiotensin-aldosterone system (RAAS) and other mechanisms.
- Acid-Base Balance Regulation: The kidneys help regulate the pH balance of the blood by excreting hydrogen ions (acid) and reabsorbing bicarbonate ions (base), thereby maintaining overall acid-base balance.
- Production of Hormones: The kidneys produce several hormones essential for various bodily functions, including:
- Erythropoietin (EPO): Facilitates the production of red blood cells in the bone marrow, thereby supporting the maintenance of adequate oxygen levels in the bloodstream.
- Renin: Regulates blood pressure by controlling the balance of sodium and water in the body through the RAAS.
- Calcitriol (Active Vitamin D): Helps regulate calcium and phosphate metabolism, supporting bone health and other physiological processes.
- Excretion of Metabolic Waste: Besides filtrating waste products from the blood, the kidneys also expel various metabolic waste substances, including ammonia and uric acid, through urine.
- Gluconeogenesis: The kidneys can produce glucose through a process called gluconeogenesis, helping maintain blood sugar levels during fasting or starvation.
- Activation of Vitamin D: The kidneys convert inactive vitamin D (calcidiol) into its active form (calcitriol), which is essential for calcium absorption in the intestines and maintaining bone health.
Symptoms of a kidney problem
Symptoms of kidney problems can vary depending on the specific condition and the severity of the problem. However, some common kidney symptoms include:
- Edema or swelling in the face, hands, legs, ankles, or feet. This swelling may be due to fluid retention caused by impaired kidney function.
- Changes in Urination:
- Increased urinary frequency (especially at night or nocturia)
- Increased urinary urgency.
- Difficulty or pain during urination.
- Reduced urine output or dark, bloody or foamy urine
- Fatigue and Weakness (even with adequate rest)
- Persistent metallic taste in the mouth
- Muscle cramps, twitching, or weakness (especially in the legs): these may occur due to electrolyte imbalances often associated with kidney dysfunction.
- High Blood Pressure or Hypertension
- Pain in the back (near the kidneys) or in the sides (flank area) that may be dull, persistent, or severe.
- Difficulty breathing or shortness of breath (especially when fluid buildup occurs in the lungs because of kidney-related issues)
- Nausea and Vomiting
- Loss of appetite
- Unexplained weight loss
- Pruritus or Persistent itching, often accompanied by dry skin, can result from the accumulation of products and toxins in the bloodstream due to kidney damage or kidney dysfunction.
- Cognitive issues like trouble concentrating, mental fog and confusion: Such occurrences may occur in late-stage kidney disease due to the accumulation of toxins in the bloodstream.
Please remember that these symptoms could be indicative of other medical conditions and experiencing one or more of these symptoms does not necessarily mean you have a kidney problem. If you experience persistent or concerning symptoms, you should immediately consult with a doctor for proper diagnosis and timely medical interventions. Early detection and treatment of kidney problems can help prevent complications and preserve kidney function.
What causes kidney damage?
Several factors can contribute to kidney damage, also known as chronic kidney disease (CKD). Here's a breakdown of the leading causes of kidney diseases:
- Hypertension or High BP: Uncontrolled BP or high blood pressure puts excessive strain on the delicate blood vessels in the kidneys, hindering their ability to filter waste effectively.
- Diabetes: High blood sugar levels from poorly managed diabetes can damage the glomeruli, the tiny filters within the nephrons.
- Glomerulonephritis: This is an inflammation of the glomeruli, often caused by autoimmune disorders, infections, or certain medications.
- Urinary Tract Blockages: Blockages caused by kidney stones, blood clots, or enlarged prostate can impede urine flow, leading to backup and potential kidney damage.
- Polycystic Kidney Disease (PKD): This is an inherited condition characterized by the development of cysts in the kidneys, progressively damaging the organ's structure and function.
- Infections: Severe or recurrent infections, such as urinary tract infections or kidney infections (pyelonephritis), can cause inflammation and damage to the kidneys.
- Autoimmune Disorders: Autoimmune conditions like lupus or autoimmune vasculitis can lead to inflammation and damage to the kidneys.
- Toxic Substances: Exposure to certain medications, chemicals, or toxins, including some over-the-counter drugs, illegal substances, and environmental pollutants, can damage kidney tissues.
- Trauma or Injury: Direct trauma to the kidneys, such as from accidents or physical injuries, can cause kidney damage.
- Genetic Factors: Inherited conditions, such as polycystic kidney disease or Alport syndrome, can predispose individuals to kidney damage.
- Dehydration: Severe dehydration, especially if prolonged, can lead to kidney damage due to reduced blood flow and impaired kidney function.
- Medical Conditions: Certain medical conditions, such as heart disease, liver disease, or severe infections, can indirectly affect kidney function and contribute to kidney damage.
- Certain medications, long-term use of pain relievers, and a family history of kidney disease can also increase the risk.
- Lifestyle choices such as smoking, unhealthy diet high in sodium and protein, and obesity can lead to kidney diseases or chronic kidney disease
- Aging: As individuals age, the kidneys may undergo structural changes and functional decline, increasing the risk of kidney damage and disease
Common Kidney Disorders and Kidney Diseases:
Some common kidney disorders and kidney diseases include:
Chronic Kidney Disease (CKD): This condition involves a gradual deterioration of kidney function over time, commonly associated with underlying conditions such as high blood pressure or diabetes.
Acute Kidney Injury (AKI): Acute Kidney injury refers to sudden kidney damage or failure, often caused by severe infection, dehydration, or certain medications.
Kidney Stones: Renal stones are solid, dense formations originating within the kidneys due to the concentration of minerals and salts in urine. They exhibit a range of sizes, from as small as a grain of sand to as large as a marble. While small stones might pass unnoticed, larger stones can cause severe pain as they move through the urinary tract
Polycystic Kidney Disease (PKD): This is a hereditary ailment marked by the emergence of numerous cysts in the kidneys, causing kidney enlargement and eventual kidney failure.
Diabetic Neuropathy: Diabetes is a major health concern in India, and a common complication is diabetic nephropathy. This happens when high blood sugar damages the tiny blood vessels in your kidneys, eventually leading to kidney failure.
Hypertensive Nephropathy: High blood pressure, also called hypertension, is another big risk factor for kidney problems. Hypertensive nephropathy arises when uncontrolled high blood pressure damages the blood vessels in your kidneys, causing them to function poorly.
Glomerulonephritis: The inflammation of the glomeruli, the minute filtering components situated in the kidneys, can compromise kidney functionality and cause proteinuria (protein in the urine), hematuria (blood in the urine), and hypertension.
Urinary Tract Infections (UTIs): This describes infections occurring anywhere within the urinary system, which includes the urethra, bladder and kidneys.
Nephrotic Syndrome: This condition is marked by increased protein levels in the urine, reduced protein levels in the blood, elevated cholesterol levels and swelling (edema).
Acidosis: Acidosis is a condition characterized by an imbalance in the body's pH levels, leading to increased acidity. Renal or kidney tubular acidosis occurs when the kidneys are unable to excrete acids properly resulting in the accumulation of acid in the bloodstream.
Uremia: Uremia develops when waste substances typically eliminated by the kidneys, like urea and creatinine, build up in the bloodstream because of kidney malfunction. This condition can result in a range of symptoms and complications, including fatigue, neurological issues, nausea and vomiting.
Hydronephrosis: This condition occurs when one or both kidneys become swollen or enlarged due to the accumulation of urine caused by an obstruction in the urinary tract. It can result from conditions such as kidney stones, tumors, or congenital abnormalities.
Pyelonephritis: Bacterial infection of the kidneys is known as pyelonephritis. This arises from a urinary tract infection (UTI) that spreads upwards to the kidneys. It can cause fever, back pain, and other symptoms.
Kidney Cysts: Kidney cysts are fluid-filled sacs that can develop in the kidneys. They may be simple cysts, which are usually benign and asymptomatic, or polycystic kidney disease (PKD), a genetic condition distinguished by the growth of numerous cysts in the kidneys, leading to kidney enlargement and dysfunction.
Azotemia:Azotemia signifies heightened levels of nitrogen-containing substances like urea and creatinine in the bloodstream. It can occur due to kidney dysfunction or failure, dehydration, or other factors.
Kidney Cancer: Kidney cancer, medically termed renal cell carcinoma (RCC), emerges when malignant cells proliferate uncontrollably within the kidney. The predominant types of kidney cancer include:
- Renal Cell Carcinoma (RCC): This type of kidney cancer constitutes approximately 85% of cases. Renal Cell Carcinoma originates in the lining of the kidney's tubules.
- Transitional Cell Carcinoma (TCC): Transitional Cell Carcinoma is relatively uncommon compared to Renal Cell Carcinoma or RCC. TCC arises in the renal pelvis, the area where urine accumulates before passing into the ureter.
What are Renal Function Tests? Which categories of renal function tests are used to gauge kidney function?
Kidney Function Test or Renal Function Tests (RFTs) are a battery of tests aimed at assessing the health and function of the kidneys. These tests provide valuable information about how effectively the kidneys filter toxins and waste products from the bloodstream, maintain electrolyte balance, and regulate fluid levels in the body. Renal Function Tests are used for Assessment of Kidney Function, Detection of Kidney Disease, Preoperative Evaluation, Assessment of Electrolyte Imbalance and Screening for Kidney Disorders. Kidney Function Tests typically include both blood and urine tests which are as follows:
Blood tests:
- Glomerular Filtration Rate (GFR) : This is an estimate of how efficiently your kidneys are filtering waste products. It's calculated using your blood creatinine level, age, gender, and race. A GFR below 60 for several months indicates CKD. - Serum Creatinine: This assessment determines the quantity of creatinine, a metabolic waste product usually filtered out by the kidneys. Elevated levels of creatinine may suggest reduced kidney function. However, other factors like age, sex, muscle mass, and medications can also influence creatinine levels. - Blood Urea Nitrogen (BUN): It is another waste product eliminated by the kidneys. However, BUN levels can be influenced by other factors besides kidney function, so it's often used in conjunction with other tests. - Electrolytes: Tests measure blood levels of electrolytes like sodium, potassium, and phosphorus, which are regulated by the kidneys. Abnormalities in electrolyte levels can indicate kidney-related or systemic disorders affecting electrolyte balance. - Serum Calcium and Phosphorus: The kidneys are vital for regulating the balance of calcium and phosphorus in the body. Imbalances in the levels of these minerals in the bloodstream can indicate advanced kidney disease. Imbalances of calcium and phosphorus can also potentially cause bone complications like renal osteodystrophy.
Urine Tests:
- Urinalysis : This is done to analyze your urine for abnormalities like protein, blood, or white blood cells. TThe detection of protein in urine or proteinuria may indicate kidney impairment. Furthermore, it can identify irregularities like hematuria (blood in urine), urinary tract infections and proteinuria which may hint at kidney issues.
- Microalbumin : Microalbumin is a highly sensitive indicator of kidney impairment compared to total protein or albumin alone. Increased levels of microalbumin in urine, referred to as microalbuminuria, frequently serve as an initial indication of kidney dysfunction, particularly in conditions such as diabetes.
- Urine Creatinine Level : Urine creatinine levels are typically measured and compared alongside a blood creatinine level to calculate the GFR more accurately.
- Urine Albumin-to-Creatinine Ratio (ACR) : This is performed to measure the amount of albumin (a protein) in the urine relative to creatinine. It's used to detect and monitor proteinuria, which is an early sign of kidney damage. Elevated ACR levels may indicate kidney disease, particularly in individuals with diabetes or hypertension.
- Autoantibody testing : Autoantibody testing refers to the examination of particular antibodies present in the blood, which are linked to autoimmune kidney conditions. These antibodies include antinuclear antibodies (ANA), anti-double-stranded DNA antibodies (anti-dsDNA), anti-neutrophil cytoplasmic antibodies (ANCA), and anti- glomerular basement membrane (anti-GBM) antibodies.
How is kidney disease diagnosed?
Diagnosing kidney diseases typically involves a combination of overview of medical history, familial history of kidney disorders, physical examination, laboratory tests and imaging studies.
Apart from discussing symptoms, risk factors and medical history with the patient, the doctor will also look for signs of kidney problems such as swelling (edema), high blood pressure or abnormal heart sounds by performing a physical examination.
Renal function tests which are a combination of a group of blood tests and urine tests are the go to for diagnosing kidney diseases. Apart from the kidney function tests or renal function tests, imaging tests and biopsies may be needed .
Imaging tests:
- Ultrasound : Ultrasound scans can generate intricate images of the kidneys and urinary tract. It can help identify structural abnormalities, kidney stones, or obstructions.
- CT Scan or MRI : These imaging tests may be used for more detailed evaluation of kidney structure, especially in cases where ultrasound results are inconclusive or further detail is needed.
Kidney Biopsy:
In certain instances a kidney biopsy may be essential to retrieve a small kidney tissue sample for examination under a microscope. This procedure is typically performed using imaging guidance to ensure accuracy and safety. A biopsy can help diagnose specific kidney diseases and determine the appropriate treatment.
Depending on the suspected underlying cause of kidney disease, additional tests such as genetic testing or specialized blood tests may also be performed.
The specific diagnostic tests you'll undergo will depend on your individual situation and medical history.
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Frequently Asked Questions
Can kidney disease be cured?
Kidney disease cannot typically be cured, but early detection and treatment can help manage symptoms and slow the progression of the disease. However, chronic kidney disease (CKD) often requires ongoing management to prevent complications. In cases of complete kidney failure, dialysis or a transplant is needed for survival. In some cases, kidney function may improve with proper medical intervention and lifestyle changes.
What are the risk factors for kidney disease?
Common risk factors for kidney disease include:
- Diabetes
- High blood pressure or high BP
- Family history of kidney disease
- Obesity
- Lifestyle choices such as smoking and drinking
- Aging
- Individuals from certain ethnic backgrounds such as African American, Hispanic or Native Americans are more prone to developing kidney disease
What is a kidney transplant?
A kidney transplant is a surgical procedure where a healthy kidney from a donor (living or deceased) is placed in the recipient's body to replace a failing kidney. A kidney transplant can restore kidney function and improve quality of life for individuals with end stage renal disease.
What are common kidney diseases?
Common kidney diseases include chronic kidney disease (CKD), diabetic nephropathy, polycystic kidney disease (PKD), glomerulonephritis, kidney stones, kidney infections and urinary tract infections (UTIs).
What is dialysis?
Dialysis is a medical treatment used to artificially filter or remove waste products and excess fluid from the blood when the kidneys can no longer perform this function adequately. There are two main types of dialysis:
1. Hemodialysis - This type of dialysis uses a machine to filter the blood
2. Peritoneal dialysis - This type of dialysis uses the lining of the abdomen (peritoneum) as a filter.
Dialysis is often used as a temporary measure for individuals with kidney failure while awaiting a transplant or as a long-term treatment option.
