reabsorpcj

Reabsorpcj (reabsorption) is the physiological process by which filtered substances in the kidney are moved from the filtrate back into the bloodstream, thereby conserving essential nutrients and maintaining fluid and electrolyte balance. It occurs along segments of the renal tubule, including the proximal tubule, loop of Henle, distal tubule, and collecting duct, and is largely responsible for reclaiming most of the filtered load.

Reabsorption relies on transcellular and paracellular transport. In many segments, active transport is driven by basolateral Na+-K+-ATPase and coupled transporters, while water moves by osmosis through aquaporin channels. Substrates such as glucose and amino acids are reclaimed via specific co-transporters (for example, SGLT proteins in the proximal tubule).

Major substances reabsorbed include water, sodium, chloride, bicarbonate, potassium, glucose, and amino acids. Reabsorption of bicarbonate helps regulate acid-base balance, while urea is variably reabsorbed in the inner medulla, contributing to the medullary osmotic gradient.

Hormonal regulation adjusts reabsorption to match body needs. Aldosterone increases sodium reabsorption and potassium secretion in the distal nephron; antidiuretic hormone promotes water reabsorption in collecting ducts; parathyroid hormone increases calcium reabsorption in the distal tubule. Hormonal signals thus fine-tune the volume and composition of body fluids.

Clinical relevance: Disturbances in reabsorption can cause dehydration, electrolyte imbalances, or acid-base disorders. Diuretics target reabsorption at various nephron sites to promote urine formation. Understanding reabsorption is essential for interpreting kidney function tests and managing conditions affecting fluid balance.