Insulin signal transduction pathway is secreted after glucose enters the beta cell and that triggers several other processes in a chain reaction. While insulin is secreted by the pancreas to lower blood glucose levels, glucagon is secreted to raise blood glucose levels. This is why glucagon has been known for decades as a counter-regulatory hormone. When blood glucose levels are low, the pancreas secretes glucagon, which in turn causes the liver to convert stored glycogen polymers into glucose monomers, which is then released into the blood. This process is called glycogenolysis. Liver cells, or hepatocytes, have glucagon receptors which allow for glucagon to attach
Hormone hormones, are lipid-soluble; to allow for their widespread distribution, these hormones must bond to carrier plasma glycoproteins (e.g., thyroxine-binding globulin (TBG)) to form ligand-protein complexes. Some hormones are completely active when released into the bloodstream (as is the case for insulin and growth hormones), while others are prohormones that must be activated in specific cells through a series of activation steps that are commonly highly regulated. The endocrine system secretes hormones directly into the bloodstream, typically via fenestrated capillaries, whereas the exocrine system secretes its hormones indirectly using ducts. Hormones with paracrine function diffuse through the interstitial spaces to nearby