Blood is the major agent for the transport of materials in the body including nutrients, water, salts, and waste products. Hormones are also transported by the blood from the endocrine tissues to the target sites.
Respiratory gases; O2 and CO2 are transported by blood.
Blood helps in the body's defense against diseases.
Blood has particular proteins e.g. interferon (produced by the liver) and antitoxins (produced by blood cells). Such chemicals protect the body from nucleic acids and toxins from invading organisms.
Blood acts as a buffer to maintain the acid-base balance i.e. concentration of hydrogen and hydroxyl ions in the body.
Blood helps in maintaining the body's temperature and concentration of water and salts. Blood is also responsible for maintaining the amounts of chemicals in the body to constant or nearly constant levels. It thus helps in homeostasis.
Blood helps in the exchange of materials between blood and body tissue through blood capillaries.