Blood transports numerous substances throughout the body, including medications, water and enzymes. Blood is the primary system by which any natural or foreign substance is moved through the body system.
Blood plasma is the liquid portion of blood containing many of the substances that are typically transported through the body. Plasma is 92 percent water and contains albumin, which is a component of protein, globulins, which contain antibodies for fighting off foreign substances, and fibrinogen, which is partially responsible for the clotting ability in blood. Blood plasma also transports minerals like sodium and potassium. Further, plasma carries waste molecules as well as amino acids, lipids and glucose, which are nutrients.
Blood in organs carries other substances throughout the body system. For example, the kidneys use blood to regulate levels of toxins, salt, potassium, phosphorus and acid. Blood in the brain, particularly at the point called the blood-brain barrier, allows or prevents substances from entering the brain. However, water, nutrients and other molecules are selectively permitted through the barrier. Every cell includes a membrane, which is essentially a barrier. The barrier controls the transmission of substances into or out of organs and the blood cells themselves. This transportation system allows chemicals within medications to reach the cells they are designed to treat.