Difference Between Filtration And Reabsorption

Filtration and reabsorption are two processes that occur in the kidneys. They are essential functions that help your body maintain fluid levels, remove waste products from the blood, and regulate electrolytes such as sodium, potassium, and chloride. Knowing the difference between filtration and reabsorption can help us understand how these processes function together to maintain good kidney health.

What Is Filtration?

Filtration is a process that involves the movement of molecules and ions through a membrane, usually in the form of a filter. This process allows certain substances to be removed from the body while other substances are kept within. During filtration, pressure forces fluids through the membrane, separating components such as proteins that cannot pass through the membrane. The resulting filtrate is reabsorbed into the body or excreted through urine, sweat, and other liquids.

What Is Reabsorption?

Reabsorption is a process that occurs after filtration and involves the absorption of solutes that have already been filtered out from the fluid by the membrane. During reabsorption, molecules and ions filtered out of the fluids are transported back into the body or metabolic pathways. Reabsorption occurs in tubular and glomerular filtration, allowing substances to be recycled and reused for other processes. Reabsorption also helps maintain the balance of electrolytes in the body and other essential nutrients. It occurs in the following parts:

  • In the Proximal Convoluted Tubule (PCT)
  • In the Loop of Henle
  • In the Distal Convoluted Tubule (DCT)
  • In the Collecting Duct

Similarities Between Filtration And Reabsorption

  • Steps of urine formation: Both filtration and reabsorption are critical steps in urine formation. In the renal corpuscle, blood pressure forces out water and waste products to create a glomerular filtrate.
  • Both take place in the nephrons: Filtration occurs in the glomerulus, a specialized area of the nephron. The reabsorption process occurs in the proximal convoluted tubule and continues through other parts of the nephron.
  • Filtration: Filtration is a passive process that involves solutes

Difference Between Filtration And Reabsorption

  • Definition: Filtration is filtering out small molecules, such as water and solutes, from a fluid system. Reabsorption is when certain substances are transported back into the bloodstream after being filtered out.
  • Governed by: Filtration is governed by hydrostatic pressure, and reabsorption is governed by osmotic pressure.
  • Occurrence: Filtration and reabsorption are both processes that occur in the kidneys to help maintain balance within the body. Filtration is a process that occurs when blood passes through the glomerulus, which is a capillary network found in the nephrons, and wastes are filtered out of the blood. Reabsorption is a process by which some of these filtered wastes are reabsorbed back into the blood from the renal tubule in the nephrons.
  • Function: The primary function of filtration is to remove toxins, waste products, and excess water from the blood. This helps maintain an optimal balance for the body’s electrolytes, hormones, and other molecules. Reabsorption occurs when the kidney tubules reabsorb some of the water and small molecules filtered out of the blood back into the bloodstream. This process helps to conserve these molecules so that they can be used by the body again.
  • Active/passive process: Filtration is a passive process, meaning it requires no energy expenditure by the body. This process involves the movement of small particles and molecules from the blood into the tubules of the nephron. Reabsorption, on the other hand, is an active process.
  • Correspondence: Filtration and reabsorption are two processes that are essential to the functioning of the kidneys. The first process, filtration, is where blood is filtered through a network of tiny vessels called nephron capillaries. This allows for waste products and other unwanted substances to be removed from the body. The second process, reabsorption, is when the kidneys actively absorb essential substances like glucose, amino acids, and electrolytes into the blood.
  • Product: In filtration glomerulus, a diluted solution reabsorption makes the urine more concentrated.
  • Selectivity: In filtration, most molecules are filtered, and in reabsorption, molecules are filtered selectively.


How do nephrons filter blood?

The nephrons, the functional units of the kidneys, are responsible for filtering blood. They perform this task through a process known as filtration. Blood is forced into a specialized structure in the nephron called the glomerulus, where small molecules such as waste products and electrolytes pass through microscopic pores into surrounding tubules.

Where does filtration occur in the kidneys?

Filtration occurs in the glomeruli, where the blood is filtered, and waste products are moved into the nephrons.

What is glomerular secretion?

Glomerular secretion is a process by which soluble molecules are removed from the body’s blood and passed into the filtrate in the renal tubules.

Why is urea more concentrated in the urine than the filtrate?

Urea is more concentrated in the urine than in the filtrate because of selective reabsorption in the kidneys.


Filtration and reabsorption are two essential processes for the excretory system. Filtration is the process by which fluid from the bloodstream is filtered through tiny holes in the glomerular capillaries to collect waste products from the body. Reabsorption is how nutrients, salts, and glucose are reabsorbed into the bloodstream from the renal tubule. Filtration and reabsorption work together to ensure that only waste products are excreted, and that essential nutrients, salts, and glucose remain in the body. Both processes play an important role in maintaining homeostasis.

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