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Urine Formation Processes

1. Urine Formation Processes

  • Most substances in the plasma except for proteins and blood cells are freely filtered into the Bowmans capsule.
  • The filtrate is modified by tubular reabsorption of water and some solutes into capillaries and by secretion of other substances from the peritubular capillaries into the tubule
  • Urinary excretion rate of a substance = Glomerular filtration rate - tubular reabsorption rate + tubular secretion rate.



a. Filtration- Water & solutes smaller than proteins are forced through the capillary walls and pores (of the glomerulus) into the renal tubule (Bowman’s capsule).

b. Reabsorption- Water, glucose, amino acids & needed ions are transported out of the filtrate into the peritubular capillary cells and then enter the capillary blood.

c. Secretion- Hydrogen ions, Potassium ions, creatinine & drugs are removed from the peritubular capillaries (blood) and secreted by the peritubular capillary cells into the filtrate.