Blood sugar level several interacting systems, of which hormone regulation is the most important. There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels: These hormones are secreted from pancreatic islets which are bundles of endocrine tissues. There are four types of pancreatic islets, alpha (A) cells, beta (B) cells, Delta (D) cells and F cells. Glucagon is secreted from alpha cells, while insulin is secreted by beta cells. Together they regulate the blood-glucose levels through negative feedback, a process where the end product of one reaction stimulates the beginning of another reaction. In blood-glucose levels, insulin lowers the concentration
Organ procurement In the United States in 2016, there were 19,057 kidney transplants, 7,841 liver transplants, 3,191 heart transplants, and 2,327 lung transplants performed. Organ procurement is tightly regulated by United Network for Organ Sharing (UNOS). In the United States, there are a total of 58 Organ Procurement Organizations (OPOs) that are responsible for evaluating the candidacy of deceased donors for organ donation as well as coordinating the procurement of the organs. Each OPO is responsible for a particular geographic region and is under the regulation of the Organ Procurement and Transplantation Network. The United States is divided into 11 geographic regions