Gene The smallest subunit of a chromosome that contains a genetic message. Glomerulus The highly vascular structure in the kidney where much of the fluid portion of the blood (serum) is filtered and passes into the kidney tubules, carrying with it toxins and many other materials present in the serum. Glomerular filtration The first step in urine formation in which blood enters the vascularized glomerulus where water and small molecules are forced by hydrostatic pressure across the glomerular filter and into the filtrate of the Bowman's capsule of the renal tubule. Glucuronidation The process of adding glucuronide to a toxicant or Phase I metabolite during Phase II biotransformation. Glucuronide A glycosidic compound of glucuronic acid.  Generally inactive.  Constitutes the major portion of some metabolites. Glutathione The tripeptide glutamyl-cysteinyl-glycine.  It is found in most tissue, especially the liver.  It plays a major role in detoxication and cellular protection.