The kidneys help remove waste products from the body, maintain balanced electrolyte levels, and regulate blood pressure.
The kidneys are a pair of bean-shaped organs located below the rib cage, one on each side of the spine.
This article looks at the structure and function of the kidneys, the diseases that affect them, and how to keep them healthy.
The
Each kidney is approximately 3 centimeters (cm) thick, 6 cm wide, and 12 cm long. Across all sexes and weights, the left kidney is 10 grams (g) heavier than the right kidney.
The kidneys are two bean-shaped organs that are roughly the size of a fist. A tough, fibrous renal capsule surrounds each kidney and provides support for the soft tissue inside. Beyond that, two layers of fat serve as further protection. The adrenal glands lie on top of the kidneys.
Inside the kidneys are a number of pyramid-shaped lobes. Each consists of an outer renal cortex and an inner renal medulla. Nephrons flow between these sections. Each nephron includes a filter, called the glomerulus, and a tubule.
The glomerulus filters blood, which enters the kidneys through the renal arteries and leaves through the renal veins. The kidneys are relatively small organs, but they receive
The tubule returns necessary substances to the blood and removes waste that then becomes urine. The kidneys excrete urine through the ureter, a tube that leads to the bladder.
What does a kidney look like?
The main role of the kidneys is to maintain homeostasis. They manage fluid levels, electrolyte balance, and other factors that keep the internal environment of the body consistent and comfortable.
These organs carry out a wide range of bodily functions.
Waste excretion
The kidneys
Some major compounds that the kidneys remove are:
- urea, which results from the breakdown of proteins
- uric acid from the breakdown of nucleic acids
- drugs and their metabolites
Reabsorption of nutrients
The kidneys
Maintaining pH
In humans, the range of acceptable pH levels is
The kidneys and lungs help keep the body’s pH stable. The lungs achieve this by moderating the concentration of carbon dioxide in the blood. The kidneys manage the pH by reabsorbing and producing bicarbonate from urine, which helps neutralize acids.
The kidneys can
Osmolality regulation
Osmolality is a measure of the body’s electrolyte-water balance, which is the ratio between fluids and minerals in the body. Dehydration is a primary cause of electrolyte imbalance.
If osmolality rises in the blood plasma, the hypothalamus in the brain responds by passing a message to the pituitary gland. This gland releases antidiuretic hormone (ADH). In response to ADH, the kidney makes several changes, including:
- increasing urine concentration
- increasing water reabsorption
- reopening portions of the collecting duct that water cannot normally enter, allowing water back into the body
- retaining urea in the medulla of the kidney rather than excreting it, as this compound draws in water
Regulating blood pressure
The kidneys regulate blood pressure when necessary, but they are responsible for slower adjustments.
They adjust long-term pressure in the arteries by causing changes in the fluid outside of cells. The medical term for this fluid is extracellular fluid. These fluid changes occur after the release of a vasoconstrictor called angiotensin II. Vasoconstrictors are hormones that cause blood vessels to narrow.
These hormones play a role in increasing the kidneys’ absorption of sodium chloride, or salt. This absorption effectively increases the size of the extracellular fluid compartment and raises blood pressure. Anything that alters blood pressure, including excessive alcohol consumption, smoking, and obesity, can
Secretion of active compounds
The kidneys release several important compounds, including:
- Erythropoietin: This controls erythropoiesis, which is the production of red blood cells. The liver also produces erythropoietin, but the kidneys are its main producers in adults.
- Renin: This enzyme helps manage the expansion of arteries and the volumes of blood plasma, lymph, and interstitial fluid. Lymph is a fluid that contains white blood cells, which support immune activity, and interstitial fluid is the main component of extracellular fluid.
- Calcitriol: This is the hormonally active metabolite of vitamin D. It increases both the amount of calcium that the intestines can absorb and the reabsorption of phosphate in the kidney.
A range of diseases can affect the kidneys. Environmental or medical factors may lead to kidney disease, and they can cause functional and structural problems from birth in some people.
Diabetic nephropathy
In people with diabetic nephropathy, damage occurs to the capillaries of the kidney as a result of long-term diabetes. The symptoms may not become apparent until
- fluid buildup
- sleep difficulty
- poor appetite
- upset stomach
- weakness
- difficulty concentrating
Kidney stones
Stones can form as a solid buildup of minerals in the kidneys.
They can cause intense pain and might affect kidney function if they block the ureter.
Kidney infections
Kidney infections tend to result from bacteria in the bladder that transfer to the kidneys.
The symptoms can include lower back pain, painful urination, and, sometimes, fever. Changes in the urine may include the presence of blood, cloudiness, and an unusual odor.
Kidney infections are
Renal failure
In people with renal failure, the kidneys become unable to filter out waste products from the blood effectively.
If an acute kidney injury occurs due to low blood pressure, dehydration, or certain medications, the condition may be reversible with treatment.
If the cause is a disease, however, kidney failure often does not have a full cure.
Kidney hydronephrosis
Hydronephrosis means “water in the kidney.”
It usually occurs when an obstruction prevents urine from leaving the kidney, causing intense pain.
In time, untreated hydronephrosis can put pressure on a person’s kidneys and may result in kidney damage.
Interstitial nephritis
A reaction to medications or infection can cause inflammation of the nephrons.
The treatment usually involves addressing the cause of inflammation or changing a course of medication.
Kidney tumor
These tumors can be benign or malignant. Benign cancers do not spread or attack tissue, but malignant cancers can be aggressive.
The
Nephrotic syndrome
When damage to the kidney affects its function, this causes protein levels in the urine to increase. This effect leads to a protein shortage throughout the body, which draws water into the tissues. The symptoms of nephrotic syndrome can include:
- puffy eyes
- increased cholesterol levels
- weight gain
- fatigue
- loss of appetite
- foamy urine
- swelling of the legs
There are many different causes of kidney damage.
Some common causes of acute kidney damage may include:
- reduced blood flow to the kidney, caused by:
- severe dehydration
- the heart not being able to pump blood effectively due to various reasons, such as heart failure
- certain medications, such as nonsteroidal anti-inflammatory drugs and some diuretics
- inflammation of the filters, blood vessels, and other structures in the kidney
- underlying health conditions, such as an enlarged kidney, a tumor in the pelvis, or kidney stones
Chronic kidney damage can often develop as a result of a combination of social, environmental, and physical factors. Factors that can increase the risk of developing chronic kidney damage include:
- diabetes
- heart disease
- high blood pressure
- obesity
- smoking and the use of other tobacco products
Excessive alcohol use can also damage the kidneys.
Certain health conditions can lead to chronic kidney damage, including:
- glomerular disease, including IgA nephropathy and glomerulonephritis
- polycystic kidney disease
- autoimmune conditions such as lupus
- severe infections, such as sepsis
- kidney cancer
- kidney stones
- frequent urinary tract infections (UTIs)
- long-lasting or untreated UTIs
In the case of severe kidney damage, dialysis might be an option. Doctors only use this treatment for end stage kidney failure involving the loss of 85% to 90% of kidney function.
Kidney dialysis aims to complete some of the functions of a healthy kidney. These include:
- removing waste, excess salt, and water
- maintaining the correct levels of chemicals in the blood, including sodium, bicarbonate, and potassium
- maintaining blood pressure
The two most common types of kidney dialysis are:
Hemodialysis
An artificial kidney, or hemodialyzer, removes waste, additional fluids, and chemicals. The treating doctor makes an entry point in the body by connecting an artery and a vein under the skin to create a larger blood vessel.
Blood travels into the hemodialyzer, receives treatment, and then returns to the body. This process usually takes place three or four times per week.
Peritoneal dialysis
The doctor inserts a sterile cleansing solution into the abdominal cavity around the intestine. This is the peritoneum, and a protective membrane surrounds it.
In continuous peritoneal dialysis, the fluid drains through a catheter. The individual discards these fluids four or five times per day. In automated peritoneal dialysis, the fluid also drains through a catheter, and the exchanges usually occur throughout the night while the person sleeps.
The following are
- Eating a balanced diet: Many kidney problems result from high blood pressure and diabetes. As a result, maintaining a nutritious, well-balanced diet can help prevent several common causes of kidney disease. The
National Heart, Lung, and Blood Institute recommends the DASH diet for maintaining healthy blood pressure. - Getting enough exercise: Exercising for 30 minutes every day can reduce the risk of high blood pressure and obesity, both of which put pressure on kidney health.
- Drinking plenty of water: Fluid intake, especially of water, is important. People can aim to drink around 6 to 8 glasses of water per day. However, those with chronic kidney disease with heart failure or swelling may be required to limit their water intake.
- Limiting salt: People should aim to limit their sodium intake. There are varied guidelines for how much salt a person should consume each day, but the general goal is less than 2 grams (g) of dietary salt per day. Other recommendations suggest a maximum of
2.3 g per day. - Moderating alcohol: Consuming more than one drink per day for females and two per day for males can harm the kidneys and impair renal function.
- Avoiding smoking: Tobacco smoke restricts blood vessels. Without an adequate blood supply, the kidneys will not be able to complete their normal work.
- Screening for health conditions: Anyone with high blood pressure or diabetes should consider discussing regular kidney screening with a doctor to help spot any possible health issues.
- Managing diabetes and heart disease: Following a doctor’s recommendations for managing these conditions can help protect the kidneys in the long term.
- Taking steps to get quality sleep and control stress: The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommends getting 7 to 8 hours of sleep each night and seeking out activities to reduce stress.
Keeping the kidneys in full working order is essential for overall health.
The kidneys are a pair of bean-shaped organs that sit just below the rib cage. They play an important role in the body, helping to remove waste products from the body, maintain electrolyte levels, and regulate blood pressure.
There is a range of conditions and diseases that can affect the kidneys, including kidney stones, kidney infections, and kidney failure, to name a few.
A person can help maintain kidney health by eating a balanced diet, exercising frequently, and managing underlying health conditions.