koncentrationsorgan

Koncentrationsorgan is a term used in physiology to describe an organ whose primary function is to increase the concentration of substances within a body fluid or lumen, usually by removing water or solvent and concentrating solutes elsewhere. The concept is central to osmoregulation, waste excretion, and water conservation.

The best-known example is the vertebrate kidney, which concentrates urine by reabsorbing water and solutes along the nephron. A hyperosmotic medullary gradient, generated by the loop of Henle and maintained by the vasa recta, enables the production of concentrated urine when needed, under hormonal control.

Key mechanisms include active ion transport by specific transporters, selective membrane permeability, and the action of water channels such as aquaporins. Hormonal regulation, notably antidiuretic hormone, adjusts water reabsorption in the collecting ducts to match hydration status.

In insects, Malpighian tubules operate with the hindgut to extract waste and reclaim water and ions, forming a concentrating system that minimizes water loss in arid environments. The rectal complex often completes water and ion reabsorption before excretion.

Concentration processes also occur in other organ systems and across taxa, including colonic water reabsorption in mammals and specialized renal structures in birds and amphibians, which reflect adaptations to different environments. Disruptions of concentration mechanisms can cause dehydration, electrolyte imbalance, or polyuria.

See also: osmoregulation, kidney, nephron, Malpighian tubules, antidiuretic hormone.