Blood has three primary functions. It transports oxygen to the body's cells, carbon dioxide to the lungs, and other nutrients throughout the body. Blood also helps regulate body temperature and pH balance and also protects the body from invading pathogens.
There are three major cellular components of blood, each of which has a different function. Red blood cells, which are the most abundant of the blood cells, are responsible for carrying oxygen from the lungs to the other cells in the body. White blood cells are responsible for engulfing and destroying invading bacteria, viruses and other pathogens. Platelets are responsible for forming blood clots when an injury is sustained.
The red blood cells, white blood cells and platelets all float in a fluid matrix known as plasma. In addition to providing transportation for the blood cells, plasma serves several other functions. It carries waste products from the body's cells to the kidneys, where they can be filtered out and excreted in the urine. Plasma also carries carbon dioxide back to the lungs where it can be exhaled, and it transports hormones from glands to the body's tissues and organs. Plasma has a pH of 7.35 to 7.45, and by picking up acidic and basic compounds as it travels through the body, it helps keep the body's pH within a narrow range.