# Reabsorption

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Part of the function of the kidney

Not to be confused with [Resorption](/source/Resorption).

Locations of secretion and reabsorption in the nephron

In [renal physiology](/source/Renal_physiology), **reabsorption**, more specifically **tubular reabsorption**, is the process by which the [nephron](/source/Nephron) recovers water and solutes from the [tubular fluid](/source/Tubular_fluid) (pre-urine) and returns them to the [circulating blood](/source/Circulatory_system).[1] It is called *reabsorption* (and not *absorption*) because these substances have already been absorbed once from ingested food and water (particularly in the [intestines](/source/Intestine)) and the body is reclaiming them from a fluid stream filtered out of blood in the [glomeruli](/source/Glomerulus_(kidney)) that is on its way to becoming [urine](/source/Urine).

Each day, the kidneys filter about 150 liters of blood, while only about 1.5 liters of urine is actually expelled from the body.[2] Reabsorption thus recovers a large proportion of the water filtered by the kidneys and plays a critical role in maintaining the water balance of the body.

## Mechanism

Reabsorption is driven by active [sodium](/source/Sodium) transport from the [lumen](/source/Lumen_(anatomy)) into the blood by the [Na+/K+ATPase](/source/NaKATPase) enzyme in the basolateral membrane of the [epithelial cells](/source/Epithelial_cell). The resultant sodium gradient causes water and other solutes in the filtrate to follow the sodium ions into the [peritubular capillaries](/source/Peritubular_capillaries) via [osmosis](/source/Osmosis).[3]

Renal tubules consist of a [proximal tubule](/source/Proximal_tubule), [loop of Henle](/source/Loop_of_Henle), and [distal tubule](/source/Distal_tubule). These different sections are responsible for reabsorbing different substances, at different rates.[4] Most reabsorption (about 60-70% of sodium and almost all of the glucose and amino acids) occurs in the first section, the proximal convoluted tubule. Glucose, amino acids, [inorganic phosphate](/source/Inorganic_phosphate), and some other solutes are reabsorbed via secondary [active transport](/source/Active_transport) through [cotransport channels](/source/Symporter) driven by the sodium gradient. In this section, solutes are reabsorbed [isotonically](/source/Tonicity),[3] as water follows the solutes being transported into the blood, such that the [osmotic potential](/source/Osmotic_potential) of the fluid leaving the proximal convoluted tubule is the same as that of the initial glomerular filtrate. Further on, absorption is not isotonic, as in the descending section of the loop of Henle, water is absorbed, but not solutes, so the filtrate becomes more concentrated. Finally, the thick ascending limb of the loop of Henle and distal nephron together recover the other 30-40% of sodium and other solutes.

## Renin–angiotensin system

The [renin–angiotensin system](/source/Renin%E2%80%93angiotensin_system) modulates the rate of reabsorption as a part of its role in regulating blood pressure and fluid balance in the body. The system affects reabsoprtion in the following cycle:

1. The kidneys sense low blood pressure.

1. Release [renin](/source/Renin) into the blood.

1. Renin causes production of [angiotensin I](/source/Angiotensin_I).

1. [Angiotensin-converting enzyme](/source/Angiotensin-converting_enzyme) (ACE) converts angiotensin I to [angiotensin II](/source/Angiotensin_II).

1. Angiotensin II stimulates the release of [aldosterone](/source/Aldosterone), [ADH](/source/Vasopressin), and thirst.

1. Aldosterone causes kidneys to reabsorb sodium; ADH increases the uptake of water.

1. Water follows sodium.

1. As blood volume increases, pressure also increases.

## Bladder Reabsorption

The [bladder](/source/Bladder) is able to separately reabsorb water and solutes such as drugs.[5] This mechanism is not affected by anticholingeric drugs, unlike renal reabsorption.[6] This mechanism also does not involve ADH.[7] In fully hydrated frogs, the bladder plays a significant role in reabsorbing water and electrolytes.[8] The pig urothelium expresses [AQP3](/source/AQP3), [AQP9](/source/AQP9), and [AQP11](https://en.wikipedia.org/w/index.php?title=AQP11&action=edit&redlink=1).[9]

## See also

- [Transepithelial potential difference driving reabsorption](/source/Transepithelial_potential_difference#TEPD_in_the_kidney)

## References

1. **[^](#cite_ref-1)** Skirving, Mya; Borger, Pam; Chiovtti, Tony; Duncan, Jacinta; Gerdtz, Wayne; Guay, Patrick-Jean; Martin, Genevieve; Walker, Katrina; Woolnough, Jim; Wright, Jane (2020). "Chapter 11: Regulation of Water, Salts and Gases". In Attley, Teresa; Irwin, Kirstie (eds.). *Biology WA ATAR Units 3&4* (1st ed.). South Melbourne, Victoria, Australia: Cengage Learning Australia. pp. 374, 402. [ISBN](/source/ISBN_(identifier)) [9780170452922](https://en.wikipedia.org/wiki/Special:BookSources/9780170452922).

1. **[^](#cite_ref-2)** ["Your Kidneys & How They Work"](https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work). *NIDDK*. Retrieved 20 November 2025.

1. ^ [***a***](#cite_ref-cjn_3-0) [***b***](#cite_ref-cjn_3-1) Palmer, Lawrence G; Schnermann, Jurgen (6 August 2014). ["Integrated Control of Na Transport along the Nephron"](https://pmc.ncbi.nlm.nih.gov/articles/PMC4386267/). *Clin J Am Soc Nephrol*. **10** (4). CJN: 676–687. [doi](/source/Doi_(identifier)):[10.2215/CJN.12391213](https://doi.org/10.2215%2FCJN.12391213). Retrieved 20 November 2025.

1. **[^](#cite_ref-khan_4-0)** ["Tubular reabsorption article (article)"](https://www.khanacademy.org/test-prep/mcat/organ-systems/the-renal-system/a/tubular-reabsorption-article). *Khan Academy*. Retrieved 2022-03-17.

1. **[^](#cite_ref-5)** Dalton, JT; Weintjes, MG; Au, JL (June 1994). "Effects of bladder resorption on pharmacokinetic data analysis". *Journal of Pharmacokinetics and Biopharmaceutics*. **22** (3): 183–205. [doi](/source/Doi_(identifier)):[10.1007/BF02353328](https://doi.org/10.1007%2FBF02353328). [PMID](/source/PMID_(identifier)) [7884649](https://pubmed.ncbi.nlm.nih.gov/7884649).

1. **[^](#cite_ref-6)** Oe, Hideki; Yoshiki, Hatsumi; Zha, Xinmin; Kobayashi, Hisato; Aoki, Yoshitaka; Ito, Hideaki; Yokoyama, Osamu (28 April 2021). ["Urinary reabsorption in the rat kidney by anticholinergics"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8080556). *Scientific Reports*. **11** (1) 9191. [Bibcode](/source/Bibcode_(identifier)):[2021NatSR..11.9191O](https://ui.adsabs.harvard.edu/abs/2021NatSR..11.9191O). [doi](/source/Doi_(identifier)):[10.1038/s41598-021-88738-y](https://doi.org/10.1038%2Fs41598-021-88738-y). [PMC](/source/PMC_(identifier)) [8080556](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8080556). [PMID](/source/PMID_(identifier)) [33911165](https://pubmed.ncbi.nlm.nih.gov/33911165).

1. **[^](#cite_ref-7)** Morizawa, Yosuke; Torimoto, Kazumasa; Miyake, Makito; Hori, Shunta; Gotoh, Daisuke; Tatsumi, Yoshinori; Nakai, Yasushi; Onishi, Sayuri; Tanaka, Nobumichi; Watanabe, Hiroki; Fujimoto, Kiyohide (12 September 2017). ["Role of the Urinary Bladder in Water Metabolism—How Does the Bladder Absorb Urine?"](https://www.ics.org/2017/abstract/181). *ics.org*.

1. **[^](#cite_ref-8)** Sinsch, Ulrich (January 1991). "Reabsorption of water and electrolytes in the urinary bladder of intact frogs (genus Rana)". *Comparative Biochemistry and Physiology Part A: Physiology*. **99** (4): 559–565. [doi](/source/Doi_(identifier)):[10.1016/0300-9629(91)90131-U](https://doi.org/10.1016%2F0300-9629%2891%2990131-U). [PMID](/source/PMID_(identifier)) [1679692](https://pubmed.ncbi.nlm.nih.gov/1679692).

1. **[^](#cite_ref-9)** Manso, Marian (September 2019). [*Fluid reabsorption across pig urinary bladder*](https://uwe-repository.worktribe.com/index.php/output/6633561/fluid-reabsorption-across-pig-urinary-bladder) (PhD (partial) thesis).

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Adapted from the Wikipedia article [Reabsorption](https://en.wikipedia.org/wiki/Reabsorption) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Reabsorption?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.