reabsorbs

Reabsorption is the physiological process by which substances are transported from a filtrate, lumen, or extracellular fluid back into the bloodstream or surrounding tissues after an initial uptake or filtration. This process allows organisms to conserve water, electrolytes, and nutrients and to regulate the chemical composition of body fluids. Reabsorption occurs in several organs and across different tissue barriers, including epithelial membranes of the kidneys, intestines, and choroid plexus, as well as during certain forms of gas exchange in various tissues.

In the kidneys, reabsorption is a major component of urine formation. Filtrate produced by the glomerulus enters the renal tubules, and most constituents are reabsorbed back into the blood. The proximal tubule reclaims about two-thirds of the filtered sodium and water, along with nearly all glucose and amino acids. The loop of Henle concentrates urine by reabsorbing sodium chloride in the ascending limb and water in the descending limb; the distal tubule and collecting duct reabsorb additional sodium, chloride, and water, under hormonal control by aldosterone and antidiuretic hormone (ADH).

Defects or dysregulation of reabsorption can disrupt fluid and electrolyte balance and contribute to disease. For example, insufficient ADH action leads to excessive urine production; abnormalities in transporters can cause disorders such as Fanconi syndrome or Bartter-like syndromes. In the gastrointestinal tract, reabsorption also helps reclaim water and electrolytes from digested material, contributing to stool consistency and hydration.

Beyond physiology, reabsorption is a general term used in chemistry and material science to describe the uptake of substances back into a solid, membrane, or phase after prior release, affecting processes such as filtration, separation, and adsorption equilibria.