Endocrine glands , which are glands of the endocrine system, secrete chemicals called hormones directly into the bloodstream. Although hormones are chemical substances circulating throughout the body, each type of hormone has an effect on only certain organs and tissues. Some hormones control the function of only one or two entire organs, whereas others have influence throughout the body. Hormones are considered messengers, supervising and coordinating activities throughout the body. Most hormones in humans are derived from proteins. Others are steroids, which are fatty matters derived from cholesterol.
Substantially, quite small amounts of hormones are able to trigger extremely large responses on vital processes as growth and development, reproduction, and sexual characteristics. Hormones also influence the way of energy utilization and storage and control the volume of fluid and the levels of minerals and sugar (glucose) in the blood. Hormones serve different functions in the body. The most important include the relief of inflammation, the control conduction of signals through neurons. Hormones are considered the pathways through which the nerves deliver impulses received and transmitted by the brain to the rest of the body.
Lacking the proper hormonal balance, an increased level of pain may be experienced or drug therapies including opiates and anti-depressants will never reach their full therapeutic potential. Hormones play a great role in maintaining the blood-brain barrier, the gateway through which blood and drugs must flow through in the body.
In the 19th century, all blood had been assumed to be the same, and the often tragic consequences of blood transfusions were not understood. Until 1900, When Karl Landsteiner discovered ABO blood group system. His overall research on serology ,which was simple in style and display but strong in scientific reasoning, led to identification of major blood groups such as O, A, and B types, matching tests, and following transfusion practices. Later on, Jan Jansky described classification of human blood groups of four types.
The term “blood group” refers to the entire blood group system which involves red blood corpuscles (RBC) antigens whose specificity is controlled by an allelic series of genes or linked very closely on the same chromosome. Blood types are classified according to a particular pattern of reaction based on presence or absence of specific antigens. It is important to realize that the blood group antigens are simple molecules of chemical nature located on the red blood cell (RBCs) surface (Arendrup et.al.,). The ABO blood group antigens remain of prime importance in transfusion medicine—they are the most immunogenic of all the blood group antigens. The functions of the ABO blood group antigens are not known. Individuals who lack the A and B antigens are healthy, suggesting that any function the antigens have is not important, at least not in modern times. The ABO blood group antigens also appear to have been important throughout our evolution because the frequencies of different ABO blood types vary among different populations, suggesting that a particular blood type conferred a selection advantage (e.g., resistance against an infectious disease.) Our view of blood groups has developed over years. Not only involving transfusion-related problems but also specific disease association with RBC surface antigens.