NaAufnahme

NaAufnahme, often rendered as Natriumaufnahme in German, refers to the uptake and transport of sodium ions (Na+) within biological systems. In humans, NaAufnahme encompasses the absorption of sodium from the gastrointestinal tract, its reabsorption along the kidneys, and the cellular mechanisms that maintain systemic sodium balance. Sodium is a key determinant of extracellular fluid volume, blood pressure, nerve function, and muscle activity.

In the gut, sodium absorption occurs mainly in the small intestine through multiple pathways. Transcellular routes include sodium-dependent transporters such as the SGLT1 glucose transporter and various amino acid transport systems, which couple Na+ uptake to nutrient absorption. The Na+/H+ exchanger NHE3 and paracellular pathways also contribute to epithelial Na+ movement. Basolateral Na+/K+-ATPase maintains the electrochemical gradient that drives luminal uptake, while water follows osmotically.

Renal handling of NaAufnahme is the principal regulator of body sodium balance. The majority of filtered Na+ is reabsorbed along the nephron: in the proximal tubule via Na+/H+ exchange and co-transporters; in the thick ascending limb via the Na-K-2Cl cotransporter (NKCC2); in the distal convoluted tubule via the Na-Cl cotransporter (NCC); and in the collecting duct through epithelial sodium channels (ENaC). Hormonal control, especially aldosterone and angiotensin II, increases reabsorption, whereas atrial natriuretic peptide and other signals promote excretion.

Clinical relevance includes disorders of sodium balance, such as hyponatremia and hypernatremia, and the impact of diuretics and dietary sodium intake on blood pressure and fluid status. Assessment often involves serum sodium concentration and 24-hour urinary sodium excretion. Health guidelines commonly advocate reducing excessive sodium intake to support cardiovascular and fluid-balance health.