5.4.3 pancreas & release of insulin

Question 1

beta cells

Answer 1

cells found in islets of Langerhans which secrete insulin

Question 2

glucagon

Answer 2

hormone which causes increase in blood glucose concentration

Question 3

insulin

Answer 3

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

Question 4

describe the pancreas

Answer 4

• lies below stomach
• endocrine & exocrine functions

Question 5

2 main secretions

Answer 5

1. pancreatic juices = contain enzymes secreted into small intestine
2. hormones = secreted from islets of Langerhans into blood

Question 6

exocrine function of the pancreas

Answer 6

• 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

Question 7

role of pancreatic duct

Answer 7

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

Question 8

duodenum

Answer 8

first part of small intestine

Question 9

what does the fluid from the pancreatic duct contain

Answer 9

• pancreatic amylase = carbohydrase which digests amylose into maltose
• trypsinogen = inactive protease which is converted to active form (trypsin) when it enters duodenum
• lipase = digests lipid molecules

also contains sodium hydrogencarbonate (alkaline) = neutralises contents from digestive system

Question 10

islets of Langerhans

Answer 10

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

Question 11

alpha cells

Answer 11

secrete glucagon

Question 12

beta cells

Answer 12

secrete insulin

Question 13

steps for releasing insulin from beta cells

Answer 13

1. cell membranes of beta cells contain calcium ion/potassium ion channels
2. 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
3. when glucose conc. outside of cell too high = glucose molecules move into cell
4. glucose quickly used in metabolism to produce ATP - involves glucokinase
5. extra ATP causes potassium channels to close (ATP-sensitive)
6. potassium can’t diffuse out which alters potential difference across membrane (less negative inside)
7. change in potential difference causes calcium ion channels to open
8. calcium ions enter cell & cause secretion of insulin by making vesicles containing insulin move to plasma membrane & fuse with it = release insulin by exocytosis