Secretion which is the transfer of materials from the blood and tubule cells into tubular fluid. These substances include: H+, K+, NH4+, creatine, and certain drugs such as penicillin.
Tubular secretion has 2 important outcomes :
1) the secretion of H+ ions helps control blood pH
2) the secretion of other substances helps eliminate them from the body.
As a result of tubular secretion, certain substances pass from the blood into urine and may be detected by urinalysis .
Reabsorption Routes
Along the renal tubule, tight junctions surround and join neighbouring cells to one another. The Apical Membrane contacts the tubular fluid, and the Basolateral Membrane contacts the interstitial fluid at the base and sides of the cell.
Substances being reabsorbed from the fluid in the tubule lumen can take one of two routes:
Paracellular Reabsorption - Fluid can leak between the cells of the tight junction and is thought to account for ~ 50% of the reabsorption of certain ions and the water that accompanies them via osmosis in some parts of the renal tubule Transcellular Reabsorption - a substance passes from the fluid in the tubular lumen through the apical membrane of the tubule cell, across the cytosol, and out into the interstitial fluid through the basolateral membrane.
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