Physiology comes from the Latin word physiologia meaning “natural science.” Physiology is a subset of the field of biology in which the functions of living organisms and/or their parts are studied. Therefore, blood physiology is a study of the functions and processes involving the blood. The study also pays attention to the make-up of the blood, its dysfunctions, and other types of problems.
Blood physiology reveals that the blood has a number of functions in the human body. Two key functions are supplying oxygen and nutrients to tissues, on the one hand, and removing waste products, on the other hand. In addition. blood transports hormones, for example, between organs and tissues. It also assists in transferring heat to the skin and acts as a buffer to protect the body’s pH to maintain homeostasis.
The blood makes up about 7% of the weight of a human body, with a volume of about 5.28 quarts (5 liters) in an average adult. Understanding blood physiology depends on understanding the components of blood. The blood is made up of plasma, which accounts for 55% of its volume, and cellular elements that make up the other 45%. These elements include red blood cells, white blood cells, and platelets.
Plasma has four main components. It is 90% water, but it also contains soluble proteins—for example albumin, globulin, and clotting protein, electrolytes, and elements. The albumins, produced by the liver, contribute to colloid osmotic pressure and contribute to the transport of materials such as vitamins, penicillin, fatty acids, and bilirubin. There are three categories of globulins—alpha, beta, and gamma—the latter of which plays a part in the immune system. Plasma as a whole carries carbon dioxide and oxygen, the respiratory gasses.
Red blood cells, or erythrocytes (RBCs) are the main oxygen transporters and also enable carbon dioxide removal. White blood cells, or leukocytes (WBCs) are important in allergic reactions, killing parasites, and responding to infection. Platelets, or thrombocytes, are cell fragments, and they are crucial in blood clotting.
Other important aspects of blood physiology are the ABO blood grouping and the Rhesus factor (RH factor). ABO group and RH factor both refer to antigens that characterize an individual’s blood in such a way that it can be determines if transfusion of blood from one individual to another is safe. These are not, however, the only antigens—there are more than 400 distinct blood group antigens.