Because blood flows directly to the liver from the intestines through the hepatic portal veins, a toxic substance absorbed from the digestive tract is often absorbed in the liver and does not enter other parts of the systemic circulation. Once in the liver, the substance may be either stored or detoxified and excreted into the intestinal tract. Detoxification of toxic substances before they reach the other portions of the systemic circulation is referred to as the “first-pass effect.” This effect can decrease the systemic toxicity of those substances absorbed from the digestive tract.