5.4.3 pancreas & release of insulin

cells found in islets of Langerhans which secrete insulin

hormone which causes increase in blood glucose concentration

hormone, released from pancreas, which causes blood glucose levels to decrease

• lies below stomach • endocrine & exocrine functions

• pancreatic juices = contain enzymes secreted into small intestine • hormones = secreted from islets of Langerhans into blood

• most cells in pancreas synthesise/release digestive enzymes • exocrine cells = small groups surrounding tiny tubules • each group of cells = acinus (pl. acini) • acini grouped together into small lobules separated by connective tissue • acini cells secrete enzymes they synthesise into tubule at centre • tubules from acini join to form intralobular ducts which combine to make pancreatic duct

carries fluid containing enzymes into first part of small intestine (duodenum)

first part of small intestine

• dispersed in small patches among lobules of acini • contain alpha cells & beta cells = make up endocrine tissue in pancreas

secrete glucagon

secrete insulin

• cell membranes of beta cells contain calcium ion/potassium ion channels • potassium ion channels normally open & calcium ions channels normally closed - potassium ions diffuse out = inside cell more negative - resting potential difference across cell membrane is -70mV • when glucose conc. outside of cell too high = glucose molecules move into cell • glucose quickly used in metabolism to produce ATP - involves glucokinase • extra ATP causes potassium channels to close (ATP-sensitive) • potassium can’t diffuse out which alters potential difference across membrane (less negative inside) • change in potential difference causes calcium ion channels to open • calcium ions enter cell & cause secretion of insulin by making vesicles containing insulin move to plasma membrane & fuse with it = release insulin by exocytosis