Functions of the kidney

Functions of the kidney

The performance of the kidney in the body greatly determines the quality of life you live. To understand the functions of the kidney, you have to familiarize yourself with the structure of the kidney. The kidneys are two bean-shaped structures found high in the abdominal cavity in humans. These structures have a concave and a convex border. They have different parts, which include the nephrons, renal corpuscle, renal tubules, renal cortex, renal medulla, renal pelvis, hilum, and ureter. All these parts play their individual roles in close coordination with each other. Collectively, this allows the kidneys to perform the crucial job of eliminating waste from the blood and controlling levels of water fluid in the body.

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kidney definition and function
normal function of kidney
physiological functions of the kidneys

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Purpose of the kidneys can be simply put as the following: filtering waste material from toxic materials, medicine, and food; controlling and filtering minerals from the blood; releasing hormones that aid in the production of red blood cells, regulating blood pressure and enhancing bone health. The blood flows into the kidney through the renal artery. After that, it undergoes a series of filtration to separate waste minerals and excess fluids from the blood. This process is crucial to keep a person healthy. If this process fails to be completed effectively, there is a need for one to undergo treatment to prevent accumulation of toxins and excess fluids in the body. Below are specific functions of the kidney with respect to structure.

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Structure and function of Kidney

What are the primary functions of the Kidneys? you may ask. The normal function of the kidney depends on its structures. These structures play a unique role in balancing blood pressure, red blood cell production and blood purification.


Arguably, nephrons are the most important part of the kidney. They play the role of taking in blood and metabolizing nutrients and later eliminating waste substances from the filtered blood. Each human kidney has about a million nephrons. The structure of the nephron can be defined as a long fine tubule, approximately 30-35mm long. The tube is closed at one end, expanded and folded into a bi-walled structure, resembling a cup. Each nephron has its distinct internal structures.

Renal corpuscle

Once blood flows into the nephron, it heads into the renal corpuscle or the malpighian body, which comprises two additional structures, i.e., the Bowman capsule and the glomerulus. The glomerulus is a collection of capillaries into clusters that absorb proteins moving through the renal corpuscle. Whatever fluid is left is called the capsular urine. The capsular urine is passed through Bowman capsule into the renal tubules.

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Renal tubules

These are a sequence of tubes starting after the Bowman capsule and stopping at the collecting ducts. Each of these tubules is divided into various parts namely, proximal convoluted tubule, the loop of Henle and distal convoluted tubule. At the proximal convoluted tubule, glucose, sodium, and water are absorbed back into the blood. This is followed by the absorption of chloride, potassium, and sodium into the blood, at the loop of Henle. Finally, more sodium is absorbed into the blood at the distal convoluted tubule; acid and potassium are also re-absorbed here. This process absorbs all the necessary nutrients for the body. By the time the fluid flows to the end of the renal tubule, it is diluted and rich with urea. Urea arises from the metabolism of proteins and is ejected from the body through urination.

Renal cortex

This is the outer part of the kidney. It comprises of the convoluted tubules and glomerulus. On its outer edges, a layer of fat and the renal capsule surround it. This combination forms a protective layer, guarding the kidney against external contaminants.

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Renal medulla

The kidney has a smooth internal tissue. This tissue is referred to as "renal medulla". The renal medulla contains the renal pyramids and loop of Henle.

Renal pyramids

The renal pyramid is a small structure made up of strings of tubules and nephrons. The tubules are responsible for transporting fluids in the kidney. The fluid is then moved from the nephrons towards the inner structures, which gather and ferry urine from the kidney.

Collecting ducts

Collecting ducts act as exits of filtered fluids from the nephrons. In the renal medulla, there is a collecting duct at the end of each nephron. After all the fluid has been collected in the collecting duct, it moves to the renal pelvis, which is the fluids' final stop.

Renal pelvis

The renal pelvis acts as a pathway for fluids down into the bladder. When looking at the structure of a kidney, the renal pelvis is the funnel-shaped space at the innermost section of the kidney.

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The calyces are found in the first part of the renal pelvis. The calyces are spaces shaped like cups, which collect fluids before fluids are finally moved to the bladder. In addition to this, it is in the calyces that excess fluids and waste are transformed into the urine.


This is a small opening on the inner edge of the kidney where there is an inward curve, which gives it a unique bean-like shape. Several structures pass through the hilum, including the renal pelvis, renal artery and renal vein. The renal artery transports the oxygenated blood from the heart into the kidney for filtration purposes while the renal vein transports the filtered blood back to the heart from the kidneys.


The ureter pushes urine down to the bladder, where it accumulates and is exited from the body.

These are some of the physiological functions of the kidneys. It is a better way to emphasize the importance of the kidneys to the human body. Below are some additional information on the services of the kidney.

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Red blood cell production

The kidneys produce erythropoietin hormone, which has a significant influence on the production of red blood cells in the body. The red blood cells play an important role in the transportation of oxygen in the blood. Patients suffering from kidney failure experience low levels of haemoglobin due to a reduction in the production of erythropoietin, and consequently, lead to anaemia. Their efforts to increase the haemoglobin count through the uptake of vitamin and iron supplements don’t pay much.

structure and function of kidney
kidney definition and function
normal function of kidney
physiological functions of the kidneys

Kidneys help maintain strong bones

Kidneys help maintain strong bones because kidneys transform vitamin D into an active form that is crucial for the absorption of calcium from foods. This facilitates the growth of bones and teeth while keeping them healthy and strong at all times. When there is kidney failure, there is a decrease in active vitamin D, which in turn leads to weaker bones and teeth. In adverse cases, it leads to growth retardation.

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Now that you understand kidney definition and function, you must know its importance to your general health is quite apparent. However, kidneys can also suffer from diseases. Below are some kidney diseases and their symptoms.

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Kidney stones

These are solid masses that are made of crystals and originate in your kidneys. Nevertheless, kidney stones can grow anywhere in your urinary tract, including ureters, urethra, kidneys, and bladder.


These symptoms might not show until the kidney stones begin to move down the ureters. This causes much pain, mostly experienced on one side of your back or abdomen. This pain is commonly referred to as renal colic. Watch out for these other symptoms:

  • Nausea
  • Vomiting
  • Blood in the urine
  • Frequent urge to urinate
  • Passing out small urine amounts
  • Fever and chills
  • Foul smell and discoloured urine

Urinary tract infections

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Urinary tract infection, commonly known as UTI is an infection arising from microbes. These microbes can only be seen through a microscope. In most cases, the UTI is caused by bacteria, fungi, and seldom viruses. The UTI can occur at any point in your urinary tract and is the most frequent infection in humans. There are two types of UTIs; the upper tract UTI and lower tract UTI.


  • Burning with urination
  • Increased frequency of urination without passing much urine
  • Increased urgency of urination
  • Bloody urine
  • Cloudy urine
  • Urine that looks like cola or tea
  • Urine that has a pungent odour
  • Pelvic pain in women
  • Rectal pain in men
  • Pain and tenderness in the upper back and sides
  • Chills
  • Fever
  • Nausea
  • Vomiting

Kidney Cyst

This is a fluid-filled sac that develops in your kidneys. Kidney cysts can be classified into two i.e. simple cysts and polycystic kidney disease. A simple cyst is a single cyst that forms in the kidney while polycystic kidney diseases is a condition passed down from generation to generation leading to the formation of multiple cysts on the kidneys.

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Symptoms for polycystic kidney diseases

structure and function of kidney
kidney definition and function
normal function of kidney
physiological functions of the kidneys
  • Pain in your back and side
  • High blood pressure
  • Blood in your urine

Symptoms of a simple cyst

  • Fever
  • Pain in your back or side, between your ribs and pelvis (the pain is usually dull, but it can become severe if the cyst bursts)
  • Pain in your upper abdomen
  • Swelling of the abdomen
  • Urinating more often than usual
  • Blood in your urine
  • Dark urine

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You have to put in deliberate efforts to ensure that your kidneys are protected at all times. Some of the best practices include proper dieting, exercising, drinking a lot of water, avoiding too much salt and being cautious when using medication. This should not be hard to do, now that you understand the functions of the kidney.


The information in this article is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. All content including text, graphics, images, and information contained on or available through this page is for general information purposes only.

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