The composition of filtrate changes dramatically as a result of the processes of reabsorption and secretion
Filtrate passing through Bowman's capsule has the same composition as plasma minus large proteins
Reabsorption - some substances in the filtrate cross the walls of the nephron and reenter the blood
Water is the most important molecule reabsorbed in the tubule
Glucose, amino acids, sodium, chloride, calcium, and bicarbonate are also reabsorbed
Some ions and molecules are too large to pass through Bowman's capsule, but enter the filtrate through ...
Secretion - some substances pass from the blood through the walls of the nephron and become part of the filtrate
Potassium, phosphate, hydrogen, ammonium ion, and many organic acids are secreted into the filtrate