Explain how the mammalian pancreas controls blood sugar concentration after a meal.

The pancreas consists mainly of exocrine tissue (<98%) which produces pancreatic enzymes required for digestion. The remaining endocrine tissue is organised into Islets of Langerhans which contain 5 different hormone secreting cell types. The hormones required for blood sugar concentration homeostasis are glucagon, which is released by α cells, and insulin, which is released by β cells.After a meal blood sugar concentration increases to a higher concentration than the glucose concentration in the β cells. This allows glucose from the blood to passively diffuse down a concentration gradient into the β cells. In the β cell the glucose is used to produce ATP via glycolysis and the Kreb’s cycle (i.e. cellular respiration). As ATP increases in β cell it binds to the K⁺ channels in the cell membrane causing them to close, leading to cell depolarisation. Cell depolarisation allows Ca²⁺ to enter the β cell, causing the release of insulin into the blood. In the blood insulin can access and signal many tissues (e.g. liver, muscle and adipose) to take up glucose from the blood, causing the blood sugar concentration to fall to a set level. As the blood sugar concentration falls the stimulation of the β cells reduces and release of insulin reduces and eventually stops. This is a process called negative feedback and allows the body to retain homeostasis of blood sugar levels.