 This video will cover the following objective from the Physiology of Blood Hematology. List the functions of blood. Transportation is a major function of blood and the cardiovascular system. For example, oxygen is carried by the blood from the lungs to cells throughout the body in order to support aerobic cellular respiration. And then the waste product carbon dioxide is transported in the blood to the lungs in order to remove that carbon dioxide from the body. Other wastes are transported in the blood. For example, the nitrogenous waste urea, a breakdown product formed from amino acid catabolism, is transported from the liver to the kidneys where the kidneys can remove that urea from the blood. So blood also functions to transport other nutrients aside from oxygen. For example, the nutrients coming in from the diet in the digestive system, those nutrients can be transported in the blood to cells throughout the body. Another example of blood functioning for transportation is to carry hormones from endocrine glands to target cells throughout the body in order to regulate the functions of the target cells. Defense is another major function of the blood. In particular, the leukocytes, the white blood cells, are responsible for defending against infection. Leukocytes can leave the blood and migrate into other tissues in a process we call emigration or diapodesis. The leukocytes move out of the blood and then into another tissue in order to help defend against infection such as in a wound. Leukocytes could migrate into the wound to help defend against bacteria or other pathogens that are coming into the body from the damaged skin. When leukocytes find an infection, they can defend against that infection in a variety of ways. For example, macrophages can perform phagocytosis as we see in the illustration on the bottom here. The macrophage is engulfing a bacterial cell in order to defend against infection from that bacterial cell to degrade the cell. Another example we see here is the leukocyte in eosinophil is releasing cytotoxic granules and those granules can help to destroy bacteria and defend against infection. Another major function of the blood is maintenance of homeostasis, which of course is a big picture function of the body in order to help maintain the homeostatic set point of important variables in the body. Body temperature is one good example of one of those homeostatic variables and the blood is important in transporting heat around the body. When the body is too hot, there is an increased blood flow in the skin in order to help transport heat out to the skin and radiate heat away from the body in order to help cool the body down. Maintenance of the pH of the body is another example of how the blood helps to maintain the homeostatic set point for variables in the body, the hydrogen ion concentration or the pH of the body. The blood pH is normally stabilized around 7.4 and if the blood pH starts to fall lower than 7.4, bicarbonate functions as a pH buffer. Bicarbonate can react with hydrogen ions forming carbonic acid, then carbonic acid is converted to carbon dioxide and water by the enzyme carbonic anhydrase. Carbon dioxide can then be removed from the blood in the lungs and in this way the respiratory and cardiovascular systems work together in order to help maintain the homeostasis of the pH in the body. If the blood pH starts to get too high, the respiratory system can decrease the rate at which carbon dioxide is removed from the body, decreasing the pulmonary ventilation rate. It will lead to a lower rate of removal of carbon dioxide and as more carbon dioxide stays in the blood, this will have the effect of lowering the blood pH, helping to restore the homeostatic set point of 7.4.