Tubular secretion at Distal Convoluted Tubule
Tubular secretion essentially is reabsorption in reverse and occurs in the Distal convoluted tubule (DCT). 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:
Overall ions such as potassium, hydrogen, and other substances such as creatine, ammonia and drugs are secreted into the filtrate from the blood and the secretion of these substances can be active OR passive types of transport from the blood into the Distal convoluted tubule.
Tubular secretion essentially is reabsorption in reverse and occurs in the Distal convoluted tubule (DCT). 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+ : Approximately all 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.
Overall ions such as potassium, hydrogen, and other substances such as creatine, ammonia and drugs are secreted into the filtrate from the blood and the secretion of these substances can be active OR passive types of transport from the blood into the Distal convoluted tubule.