Drag each tile to the correct box. Explain the process in which hormones secreted by the pancreas function with respect to increased glucose levels in the blood.

Glucagon is a peptide hormone secreted from the pancreatic islet alpha cells when glucose levels are less than 80 mg/dL. Glucagon circulates free in the plasma; it has a half - life of 6 minutes. Glucagon is a peptide hormone. It binds a plasma membrane receptor which initiates a second messenger signaling cascade. The target tissue for glucagon is the liver. Glucagon causes the liver to secrete glucose leading to a net decrease in stored glycogen and an increase in plasma glucose.

In the absence of insulin, glucagon is secreted. Glucagon acts in a synergistic manner with cortisol and epinephrine to raise blood glucose levels.

Endocrine pancreas produces insulin and glucagon which regulate fuel homeostasis in the fed and fasted states. Insulin is secreted primarily in response to an increased blood glucose level. Glucagon is secreted in response to decreased blood glucose level. In the fed state, insulin directs the storage of excess nutrients in the form of glycogen, triglycerides, and protein. The targets of insulin are liver, muscle, and adipose tissue. In the fasting state, glucagon directs the movement of stored nutrients into the blood. Liver is the main physiological target of glucagon. Diabetes mellitus occurs when there is a deficiency of insulin action as a result of either insufficient insulin secretion or resistance (receptor impairment) to insulin at its target tissue.

Insulin is secreted from the pancreas by a process called glucose stimulated insulin secretion (GSIS). 75% of the islet cells are β cells which produce insulin. Another 20% are α cells that secrete glucagon. The δ cells produce the paracrine, somatostatin (SRIF). Which inhibits both insulin and glucagon secretion.

Insulin is secreted in a biphasic manner. The initial burst reflects the release of preformed secretory vesicles; it lasts 5-15 minutes. The second more gradual and sustained secretion (30 min) is due to the release of newly synthesized insulin molecules.

The half life of insulin, like most protein hormones, is short. Most of secreted insulin is degraded by the liver and kidney. Insulin secretion is regulated by factors other than glucose. There are several potent inhibitors of insulin secretion including somatostatin and the catecholamines (epinephrine and norepinephrine). The primary targets for insulin are liver, skeletal muscle, and fat. Insulin has multiple actions in each of these tissues, the net result of which is fuel storage (glycogen or fat).

Glucose enters the circulation either from the diet or from synthesis in the liver. It enters all cells via the glucose transporter (GLUT). To prevent glucose from leaving the cells via this transporter, the glucose is rapidly phosphorylated to glucose-6-phosphate. There is a family of glucose transporters (e. g., GLUT 1, GLUT 2, GLUT 4). In skeletal muscle and fat cells, insulin binds to the insulin receptor which causes the active recruitment of the glucose transporter, GLUT 4, to the cell surface. Once located at the cell surface, GLUT 4 increases the amount of glucose that enters fat and skeletal muscle cells. The GLUT4 action enables a rapid removal of glucose from the circulation thereby restoring plasma levels to 80-100 mg/dL.