NEPHRONS - The Kidneys' Filtration Units

Nephrons are microscopic tube-like structures in the kidneys that filter the blood and cause wastes to be removed. They are the most basic structures of the kidney's anatomy, and are an integral part of the urinary system. Each kidney contains over one million of them.

Nephrons are the main functional units of the kidneys.

These tiny filtering units are responsible for removing harmful toxins and excess fluids from the blood, keeping it clean and maintaining its correct volume and concentration.

The process of filtering the blood is very sophisticated and is performed by a complicated process of chemical exchanges, within each nephron.

Every day, close to 200 liters of blood is processed and filtered by the kidneys. The extracted waste products and excess water form urine, which is eventually expelled from the body via the urinary tract. This entire process of extracting waste products and excess water from the blood takes place in the nephrons. This is an extremely important function and is critical for maintaining good health and sustaining life.

While they may look like tangles of vessels and tubules, nephrons have an orderly structure, designed to perform the essential process of filtering the blood.

Nephron Diagram

Basically, a nephron comprises a renal tubule and blood vessels. The renal tubule expands into a cup-shaped structure called the Bowman's Capsule, which contains a ball of capillaries known as the Glomerulus.

The Glomerulus is the primary structure of the filtering process. Glomerulus comes from the Greek word meaning "filter". The plural form of the word is "Glomeruli".

The Glomerulus filters the blood and regulates the concentration of essential substances such as potassium, calcium, and hydrogen, and removes substances not produced by the body such as drugs and food additives. The excess fluids and waste substances form what is known as urine.

The Glomerulus is contained inside a cup-shaped structure known as the Bowman's capsule. It got its name from "Sir William Bowman", a famous British physician from the eighteen hundreds. He was the first to identify this capsule, which then became known as the "Bowman's capsule".

The Bowman's capsule extends into the Renal tubule, which is a duct that transports urine out of the Bowman's capsule. The Renal tubule is approximately 3 cm long. It makes a number of turns and loops and eventually leads to the Collecting tubule, or Collecting duct.

The part of the renal tubule that loops around into a 'U' turn is called the Loop of Henle. This got its name from another famous physician, back in the eighteen hundreds, named "Frederick G. J. Henle". He was a German physician and was credited with the discovery of the "loop of Henle".


The major function of the kidney is to remove waste products from the blood and by extension, the body. Each nephron is supplied with blood from a branch of the Renal Artery. It first goes to the Glomerulus, where water and other substances such as sugar or glucose, salt, amino acids and urea are removed from the blood (filtered).

The substances extracted from the blood remain in the Bowman's Capsule... while the filtered blood moves along tiny vessels called Capillaries, and exits the kidney through the Renal Vein.

Some of the substances that are removed from the blood are useful to the body while some are not. As these substances move along the renal tubule the useful substances, such as water, salt, amino acids and glucose are reabsorbed back into the blood stream through the Capillaries.

The other substances that are not useful to the body such as excess water and salt, urea and uric acid continue to move along the renal tubule into the Collecting tubule.

These waste products form what is known as urine.

From the Collecting tubule the waste products (urine) go to the ureters then into the bladder, where it is eventually expelled from the body through the urethra.

Nephrons are the central filtration system of the kidneys that perform the crucial filtering function of the kidneys. They are responsible for filtering water, urea, salt, glucose, amino acids and other trace substances from the blood. Many of the filtered materials are then reabsorbed into the blood to be reused by the body, to maintain normal body functions. The waste materials remain behind to be excreted as waste products in the urine.

Nephrons are not only responsible for keeping the body's chemistry clean, but they also help to ensure that the correct concentration and volume of the blood are maintained.