Absorption
Resorption ( Latin resorbere ' swallow down'; PPP : resorptum → resorptio ' swallowing down') describes the absorption of substances in biological systems. In humans and vertebrates , this refers in particular to the absorption of substances from the food pulp in the intestine during digestion (for example breakdown products of food components such as carbohydrates , proteins and fats , vitamins , minerals , water , medicines, toxins and others).
In humans, resorption via the epithelia , especially in the small intestine , is of great importance. Some substances (e.g. ointments , contact poisons ) can also be absorbed through the skin .
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A distinction is made between passive and active absorption in the small intestine . In passive resorption, nutrient components and other resorbable substances are diffused from places of high concentration to places of low concentration. This happens in the small intestine, for example, where the interior space ( lumen ) has a high concentration of nutrients, the cells of the intestinal mucosa ( mucosa ) have a lower concentration. Without or against a concentration gradient, absorption can occur through active absorption. The substances to be transported are reabsorbed against the concentration gradient with the help of transport molecules (so-called "carrier proteins" ) or by consuming or splitting the energy carrier adenosine triphosphate (ATP).
Basically, after digestion, the nutrient components, such as glucose and amino acids , are first absorbed into the cells of the intestinal wall (mucosal cells) and from there transported further into the blood , which reaches the liver as portal blood . Non-polar substances such as fats are absorbed further into the lymph after absorption in the mucosal cells .
In the tubules - (see nephron ) - of the kidney , after filtration in the glomeruli (i.e. after the formation of the primary urine ), water, glucose and other vital substances are reabsorbed from the primary urine back into the blood. For example, glucose is actively reabsorbed from the primary urine into the blood.
Definitions
In English and international usage, only the terms absorption and reabsorption are used for the processes described above. This has partly also established itself in German usage. The prefix re- (= "back") results in both inelegant and misleading word formation in the word re- absorption . That is why many physiologists today advocate the consistent introduction of the English pair of terms in the German-speaking area. For example, substances would be absorbed from the intestinal lumen and reabsorbed into the blood from the kidney tubules .