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Overview of kidneys: How do they work?

Team AckoJan 17, 2024

As per the Indian Society of Nephrology (ISN) report, in India, one in every ten adults suffers from kidney disease. They also found that about 90% of these patients are unaware of their early-stage condition. This shows there is a significant lack of awareness and early intervention when it comes to kidney diseases. To create much-needed awareness, here’s an article that will give you an overview of kidneys and explain how they work.




What are kidneys?

The kidney is one of the most crucial organs in the body. There are two kidneys in the human body, and they look like beans. Kidneys are located on either side of your spine, behind your abdomen, and below your ribs. Each kidney measures approximately 4 to 5 inches in length or the size of a fist. A tough, fibrous renal capsule protects and supports the delicate tissue inside each kidney. Two more layers of fat act as extra insulation. The adrenal glands are located above the kidneys. There are several pyramid-shaped lobes inside the kidneys. Each kidney has an inner renal medulla and an outer renal cortex. These portions are connected by nephrons. A filter called the glomerulus and a tubule are both parts of a nephron. Blood is filtered in the glomerulus after it passes through the kidneys' renal arteries and veins. Despite being relatively small, the kidneys get 20–25% of the heart's output.

Why are the kidneys essential for the body?

Kidneys are essential for the body because these organs remove extra fluid and waste. A proper balance of minerals, salts, and water in your blood, including sodium, calcium, phosphorus, and potassium, is maintained by your Kidneys. They also eliminate acid that is produced by your body's cells. Your body's muscles, nerves, and other tissues could be unable to function normally without this balance of fluids.

Kidneys help in the following processes.

  • Kidneys produce important hormones.

  • They regulate blood pressure.

  • They aid in the production of red blood cells

  • They help in maintaining a healthy bone structure

What are the different functions of the kidneys?

There are numerous biological activities that these organs do. Here are some examples.

1) Removing waste from the body

The kidneys filter out different types of waste and eliminate them through the urine. Among the main substances that kidneys filter are urea and uric acid. Urea is produced when proteins break down, and uric acid is produced when nucleic acids break down.

2) Reabsorption of nutrients

The kidneys use tubules to reabsorb nutrients from the blood and transfer them to areas of the body where they are required the most. In order to maintain homeostasis, they also reabsorb other substances like amino acids, phosphate, glucose, water, magnesium, sodium, bicarbonate, potassium ions, and chloride.

3) Maintaining the pH level of the body

The pH range that is suitable for humans is 7.35 to 7.45. The body assumes an acidemic or alkalemic state at concentrations that are either below or above this range. Proteins and enzymes degrade in these conditions and stop working. This may be lethal in extreme circumstances.

The lungs and kidneys aid in maintaining the body's pH balance. The lungs manage this by regulating the blood's carbon dioxide levels. The kidneys control pH by generating and reabsorbing the acid-neutralising bicarbonate from urine. If the pH is acceptable, the kidneys can store bicarbonate and release it if the acidity level increases. They can also create new bicarbonate with acid.

4) Regulating the electrolyte-water balance in the body

Osmolality, or the ratio of bodily fluids to minerals, is a measurement of the electrolyte-water balance in the body. Dehydration can lead to an imbalance in the electrolyte-water ratio. When blood's osmolality ratio increases, the hypothalamus (a part of the brain) reacts by sending a signal to the pituitary gland. It then releases the Antidiuretic hormone, and the kidneys react by taking actions like increasing the resorption of water, increasing urine contents, and keeping urea (which helps in water reabsorption) in the kidney's medulla rather than removing it from the body. 

5) Adjusting the blood pressure in the body

When blood pressure needs to be adjusted, the kidneys are in charge of some subtle changes. They alter the fluid around cells and influence the long-term pressure in the arteries. Hormones called 'Vasoconstrictors' are responsible for the narrowing of the arteries. These hormones contribute to increased salt (sodium chloride) absorption in the kidneys. This, in turn, increases the fluid around cells, leading to higher blood pressure. Kidney diseases can result from anything that affects blood pressure, such as heavy alcohol use, smoking, and obesity.

6) Secreting essential compounds

Red blood cell production, or erythropoiesis, is regulated by the hormone Erythropoietin. The liver also produces it, but the kidneys are the primary source in adulthood. Kidneys secrete another essential enzyme called Renin. It regulates blood plasma, expansion of arteries, interstitial fluid, and lymph (A liquid that contains white blood cells. They promote immune function). Kidneys also secrete Calcitriol, which increases the intestines' capacity to absorb calcium and the kidneys' capacity to reabsorb phosphate.

How do my kidneys work?

There is an artery that connects the heart and the kidneys. They receive blood from this artery, and the filtration process begins. Millions of microscopic blood filters present in the kidneys are used to clean the blood. After the blood travels through these filters, the freshly cleaned blood enters the bloodstream, and the waste material travels through the ureter and is collected as urine in the bladder.

Around 3 litres of blood is filtered at a time, and this process takes place about 60 times in 24 hours. Thus, on average, The kidneys filter about 180 litres of fluid daily. Out of this, about 0.8 to 2 litres of fluid is excreted as urine. The bladder holds the urine until excretion.

Parts of the kidney

Internally, the kidney is divided into three parts—the outer cortex, middle medulla (it contains the renal pyramids), and innermost renal pelvis. Your kidneys receive unfiltered blood through the renal artery, and they send out the filtered blood through the renal vein. 

The kidney's filtering structures are located in the outer cortex. The medulla extends into the renal pelvis after draining the urine into tubes. The renal pelvis connects to the ureter. Urine is transported from the kidney to the bladder by the ureter.

Common tests to check the health of my kidneys

Here are the two most common types of diagnostic tests that are carried out to find kidney problems.

  1. Urine test: A protein called albumin is examined in your urine. Proteins must be found in the blood rather than the urine. If there is a presence of protein in your urine, your kidneys may not be effectively filtering your blood. An excessive amount of albumin in your urine indicates kidney disease and early kidney damage. You should repeat the test if your urine protein test results are "positive" to verify kidney issues. Three positive outcomes can detect kidney disease over three months or longer.

  2. Blood test: A Kidney Function test called a GFR (Glomerular Filtration Rate) can tell if you have renal disease and at what stage it is. Medical professionals will check your blood for a waste substance called creatinine to determine your GFR. Your kidneys may not remove creatinine from your blood effectively when they are damaged.  

A mathematical formula is applied to your creatinine result to determine your GFR. The outcome affects how much damage the kidneys have sustained.

Check out: GFR Calculator

How can I keep my kidneys healthy?

Here are some tips to keep your kidneys healthy.

  1. Diabetes and high blood pressure can contribute to numerous kidney issues. So eating a well-balanced and nutritious diet can help prevent several significant causes of kidney diseases.

  2. The risk of obesity and high blood pressure, which impose pressure on kidney health can be decreased by exercising for 30 minutes each day.

  3. It's crucial to drink enough fluids, especially water. How much water a person should consume depends on various circumstances, but 4 to 6 glasses per day can help maintain and enhance kidney health.

  4. Limit your daily salt consumption to no more than 1,500 mg.

  5. Drinking more than one alcoholic drink each day—or two for men—can damage the Kidneys and reduce their ability to function.

  6. Ibuprofen and naproxen, among other over-the-counter medications, might harm the kidneys if used in excess.

  7. To help identify potential health risks, anyone with diabetes or high blood pressure should consider routine kidney screening by discussing this with a certified doctor.

  8. Get 7 to 8 hours of sleep per night, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Exploring stress-relieving exercises can also be helpful.

Frequently asked questions

The commonly asked questions and answers about kidneys are mentioned in this section.

What is the colour of the urine during renal failure?


The increased concentration and accumulation of chemicals in urine caused by failing kidneys result in a deeper colour, which might be brown, red, or purple. High concentrations of red and white blood cells, as well as a large quantity of tube-shaped particles known as cellular casts, are the causes of the colour change.

Is kidney damage reversible?


Kidney damage is not reversible. However, the disorder does not significantly shorten the lives of most patients with Chronic Kidney Disease (CKD). Your CKD won't necessarily worsen, even if it's impossible to reverse kidney damage that has already occurred. Only a small percentage of people develop advanced CKD.

Which workout is beneficial to Kidneys?


Opt for continuous action like bicycling, walking, skiing, swimming, etc., or any other sport that requires you to move a lot of muscle continuously. Low-intensity strengthening exercises can also be beneficial to kidneys.

Disclaimer: The content on this page is generic and shared only for informational and explanatory purposes. It is based on several secondary sources on the internet. As this content piece is not vetted by a medical professional, please consult a doctor before making any health-related decisions.



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