Describe the processes of filtration, re absorption, and tubular excretion that occur during the formation of urine.
During filtration, or glomerular excretion, blood pressure forces all the small molecules in the blood into the lumen of the nephron through the pores both in the walls of the glomerular capillaries and in the wall of the Bowman's capsule. The filtrate has the same concentration of dissolved substances as the blood minus the formed elements and the plasma proteins which are too large to fit through the pores of the capillaries and the Bowman's capsule. As the filtrate passes through the tubules of the nephron, water and many dissolved materials are reabsorbed by the blood. In fact, during the filtrate's passage through the tubules up to 99 percent of the water is reabsorbed. In addition, the tubules also remove substances from the blood. This process, called tubular excretion, supplements the initial glomerular filtration.
