BlogNCERTImportant Topic of Biology: Kidney Function

Important Topic of Biology: Kidney Function

Kidneys are an organ that exists in vertebrates and invertebrates. The kidneys are two red bean-shaped organs found in all vertebrates. In adults, the kidneys are 12 inches long and are found left and right in the retroperitoneal area. Kidney arteries are responsible for the transfer of blood to the kidneys and the blood that flows through the paired arteries of the kidneys. Both kidneys are connected to the ureter, which is a tube that carries urine out of the bladder.

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    The active unit and structure of the kidneys are called the nephron. There are one million nephrons in each adult kidney. The number of kidney nephrons changes from one animal to another as in a mouse, there are only about twelve thousand five hundred nephrons.

    The kidneys are involved in various functions, such as regulating the body’s fluid volume, acid-base balance, digestion of various electrolytes, fluid osmolality, and aids in detoxification.

    Blood filtration occurs in the glomerulus when one-fifth of the volume of blood that enters the kidneys is filtered. Plain water, sugars, amino acids, sodium, and bicarbonates are examples of rehydration substances. Substances such as uric acid, ammonium, potassium, and hydrogen are extracted during filtration.

    There are also a few functions that carry the kidneys, which are independent of the nephrons. Activities such as converting vitamin D to its active form of calcitriol and the combination of the hormones erythropoietin and renin are just a few of the functions carried by independent kidneys without nephrons.

    Research on kidney function research is called Renal physiology. Nephrology is one of the specialized treatments for kidney-related diseases such as nephrotic syndromes, severe kidney damage, chronic kidney disease, pyelonephritis.

    In this article, we will discuss the definition of kidney, kidney transplantation, kidney formation, kidney function, kidney disease, and various treatments available to treat the disease.

    Kidney Definition

    The kidneys are a pair of reddish, bean-shaped organs located on both sides of the human spine, below the ribs, and behind the abdominal region.

    The kidneys are present in all vertebrates and a few vertebrates and the human kidneys are about five inches long and about the size of a large fist. Filtering blood is the main function of the kidneys. They also help drain waste, regulate body fluid balance, and help maintain a good level of electrolytes in the body. All the blood in our body passes through the kidneys a few times a day for filtration.

    When untreated blood enters the kidneys, the waste products are removed and salt, water, and minerals are needed. The filtered blood from the kidneys returns to the body and the waste products collected in the blood are converted into urine collected in the kidneys. The pelvis of the kidneys is a flexible structure that extends a tube called the ureter to the bladder.

    Kidney Structure

    In humans, the kidneys are located behind the abdominal cavity, one on each side of the spine and lying in the retroperitoneal area with a slightly inclined angle.

    The asymmetry within the abdominal cavity is due to the position of the liver which causes the right kidney to be slightly lower and smaller than the left kidney. The left kidney is most commonly found in the spinal column and the right kidney is placed deeper in the middle than the left kidney.

    The right kidney is slightly smaller than the left kidney and also lies just below the diaphragm and behind the liver. The right kidney is small as it allows the liver to be in that position.

    The left kidney resides behind the spleen and below the diaphragm. Each kidney weight reaches 125-175 grams for males and 115 to 155 grams for females. The kidneys are surrounded by a strong and fibrous renal capsule.

    There is the presence of adrenal glands above each kidney. The eleventh and twelfth ribs help protect the upper part of the kidneys.

    The adrenal glands in each kidney have two layers of fat in them which are perirenal fat and pararenal fat. Perirenal fat is located between the renal fascia and the renal capsule and pararenal fat is located above the renal fascia.

    The kidney is a bean-shaped structure with straight and convex edges. Renal hilum is a retreat in the concave border. The renal hilum is the area where the kidney vessels enter the kidneys as well as the kidneys and the leaves of the ureter.

    The kidneys are surrounded by a strong renal and fibrous capsule which is surrounded by two layers of fat such as perirenal fat and pararenal fat and the renal capsule is surrounded by renal fascia.

    Kidney Functions

    The main function of the kidneys is to contribute to the overall homeostasis of the body. The kidneys are responsible for controlling the acid-base balance, electrolyte concentration, extracellular fluid volume, and blood pressure. These homeostatic activities are performed to keep the inner body stable and comfortable.

    These homeostatic functions are performed by both kidneys independently and with the help of other organs, especially those related to the endocrine system. Many endocrine hormones bind to these endocrine functions, these include renin, angiotensin II, aldosterone, and others. The kidneys perform a variety of functions


    Kidneys help excrete waste products and excrete them. The two most important components released by the kidneys are urea and uric acid. Urea is the result of a decrease in protein and uric acid degradation of nucleic acid.


    The kidneys are also responsible for the absorption of nutrients into the bloodstream and for transporting nutrients that are taken back to the body to support health. Kidneys also absorb other products that help maintain homeostasis. Re-absorbed products include bicarbonate, amino acids, glucose, sodium, water, phosphate, chloride, sodium, magnesium, and potassium ions.

    Maintaining pH:

    The acceptable pH levels are between 7.38 and 7.42 in humans. When the pH level of the human body falls below this limit then the body enters a state of acidemia and above it can be alkalemia. Without the pH level observed in humans, proteins and enzymes break down and can no longer function properly, and in extreme cases, this condition can be fatal. Both kidneys and lungs help maintain a stable pH level in the human body. The lungs are able to maintain a pH level by measuring the saturation of carbon dioxide while the kidneys regulate pH levels through two processes which are the absorption and regeneration of bicarbonates in the urine and the release of hydrogen ions and unchanging ions. In the process of re-absorbing and re-producing bicarbonates in the urine, bicarbonates help reduce acids. The kidneys have the option to maintain their reliable source if the pH level is tolerated or to release it when the acid level rises.

    Osmolality Regulation:

    Osmolality is a measure of the body’s water-electrolyte balance or the ratio between fluids and minerals in the body. The main cause of dehydration is considered to be electrolyte imbalance. Kidneys help maintain a high level of water and salt in the body. When the level of osmolality increases in blood plasma then the hypothalamus in the brain responds by transmitting a message to the pituitary gland. The pituitary gland releases antidiuretic hormone (ADH). When ADH is removed from the body the kidneys make many similar changes

    • Increased urination concentration.
    • Increase water absorption.
    • There is a re-opening of part of the drain, which allows water to return to the body.
    • The urea in the medulla of the kidneys is pushed back rather than released, as it is absorbed into the water.

    Blood Pressure Regulation:

    If necessary, the kidneys help control the body’s blood pressure, which is also responsible for gradually correcting it. The kidneys help to regulate the long-term intensity of blood vessels by altering the fluid outside the cells. The medical name for this fluid is fluid outside the cell. Changes in extracellular fluid occur after the release of a vasoconstrictor called angiotensin II. Blood vessels narrow only because of the hormone vasoconstrictors. These hormones also work with other functions to increase kidney absorption of sodium chloride or salt. The presence of salt absorption effectively increases the size of the external fluid component and raises blood pressure. Excessive alcohol consumption, smoking, or obesity may alter blood pressure, which can lead to kidney damage.

    Storage of Hormones and Active Compounds:

    The kidneys are responsible for the release of many active compounds such as Renin, erythropoietin, and calcitriol.


    Controls erythropoiesis or the production of red blood cells. Although the liver also produces erythropoietin, the kidneys are a major producer in the adult body.


    Renin helps regulate blood vessels enlargement and volume of blood plasma, lymph, and interstitial fluid. Interstitial fluid is a major component of the fluid that flows out of the cell and lymph is a fluid that contains white blood cells and supports the immune system.


    Calcitriol is a metabolite of the vitamin D hormone. Calcitriol helps increase the amount of calcium that can be absorbed by the intestines and also helps in the absorption of phosphate by the kidneys.

    Also read: Important Topic of Biology: Renin


    What are the early signs of kidney problems?

    You can see blood in your urine and you also have foam. You will have trouble concentrating and you will experience swelling and dryness on your skin.

    Can you live without a kidney?

    It is not possible to live without the kidneys. But since we have two, it is possible to live with one kidney.

    What causes kidney problems?

    People with diseases such as diabetes and high blood pressure are more likely to have kidney problems.

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