Drugs and their metabolites can be excreted from the body by a number of routes, such as via the lungs, the skin, the bile duct and the kidneys. Drugs can also be excreted through saliva and breast milk, but these are minor excretion routes compared to the kidneys. The plasma and chemicals that have been filtered into the nephron then pass through the nephron on their route to the bladder and eventual excretion in the urine. This process of excretion explains the importance of drug metabolism to drug excretion. Drug metabolism makes a drug more polar so that it is less likely to be reabsorbed from the nephrons. The blood entering the glomeruli is under pressure and so plasma is forced through the pores in the capillary walls into the nephron, carrying with it any drugs and metabolites that might be present.