You have now explored the process of urine formation and should know that:
• the nephron modifies the composition of the blood and rids the body of wastes and toxins by producing urine. Blood composition is altered by filtration, tubular reabsorption, and tubular secretion.
• filtration is the transport of materials and dissolved substances from the blood of the glomerular capillaries into Bowman's capsule. Blood cells and plasma proteins are too large to pass through the glomerular capillary walls.
• many of the important nutrient molecules that enter the filtrate must be actively pumped back into the blood by tubular reabsorption, the bulk of which takes place in the proximal tubule.
• the loop of Henle promotes the reuptake of water and salt from the filtrate.
• the distal tubule is the site of active tubular secretion of material from the blood into the filtrate.
• when the filtrate reaches the collecting duct, most of the salt and water has already been removed. As it moves down the duct, the filtrate may become concentrated urine by the removal of water under the control of ADH (antidiuretic hormone).
