Tubular
secretion essentially is reabsorption in reverse. If failure of tubule cells to reabsorb some solutes is an important way of clearing plasma of unwanted
substances, but another way to do this is tubular secretion.
Substances such as creatine, certain organic acids H+, K+ and NH4+
either move into the filtrate from the peritubular capillaries through the tubule cells
or are synthesized in the tubule cells and secreted. As a result, the urine
eventually excreted contains both filtered and secreted substances.
Tubular secretion is important for: Disposing
of substances: Substances such as certain drugs, that are tightly bound to
plasma proteins. Because proteins are generally not filtered because of their
relative size, so the substances are unable to be filtered so it must be
secreted. Eliminating undesirable substances: Substances such as urea and uric acid are two
nitrogenous wastes, are excreted Ridding
the body of excess K+ potassium ions present in the filtrate
are reabsorbed in the PCT and ascending loop of Henle but nearly all potassium
ions in urine is from aldosterone driven active tubular secretion in to the late
DCT and collecting ducts Controlling
blood pH: hydrogen ions are secreted from the renal tubule cells into the
filtrate to retain and generate more HCO3 (base). As a result the blood pH rises
and the urine drains off the excess hydrogen ions.
secretion essentially is reabsorption in reverse. If failure of tubule cells to reabsorb some solutes is an important way of clearing plasma of unwanted
substances, but another way to do this is tubular secretion.
Substances such as creatine, certain organic acids H+, K+ and NH4+
either move into the filtrate from the peritubular capillaries through the tubule cells
or are synthesized in the tubule cells and secreted. As a result, the urine
eventually excreted contains both filtered and secreted substances.
Tubular secretion is important for: Disposing
of substances: Substances such as certain drugs, that are tightly bound to
plasma proteins. Because proteins are generally not filtered because of their
relative size, so the substances are unable to be filtered so it must be
secreted. Eliminating undesirable substances: Substances such as urea and uric acid are two
nitrogenous wastes, are excreted Ridding
the body of excess K+ potassium ions present in the filtrate
are reabsorbed in the PCT and ascending loop of Henle but nearly all potassium
ions in urine is from aldosterone driven active tubular secretion in to the late
DCT and collecting ducts Controlling
blood pH: hydrogen ions are secreted from the renal tubule cells into the
filtrate to retain and generate more HCO3 (base). As a result the blood pH rises
and the urine drains off the excess hydrogen ions.