5.4.3(The pancrease and release of insulin)

State the 2 main secretions of the pancrease

• Pancreatic juices containing enzymes

• Hormones which are secreted from islets of Langerhans into the blood

Describe what is meant by exocrine glands

• Produce and secrete extracellular secretions into ducts

State the name of the cells in exocrine glands and state what they secrete

• Acinar cells:

  • Proteases - trypsinogen

  • Pancreatic lipase

  • Pancreatic amylas

  • Sodium hydrogen carbonate

Describe the structure of the exocrine glands in the pancrease

• The exocrine cells are in small groups called acini, surrounding tubules

• The acini are grouped together into small lobules separated by connective tissue

• The cells of the acini secrete the enzymes they synthesise into the tubule at the centre of the acini

• The tubules from the acini join to form intralobular ducts that eventually combine to make the pancreatic duct

Describe the structure of endocrine glands in the pancrease

• Dispersed in small patches among the lobules of acini are the islets of Langerhans

• The islets of Langerhans conatain alpha cells and beta cells which make up the endocrine tissue

State what the alpha and beta cells in the endocrine tissue secrete

• Alpha - glucagon

• Beta - Insulin

Describe the process of insulin release by beta cells when blood glucose concentration increases

• Cell membranes of beta cells contain calcium and potassium ion channels

• The potassium channels are normally open and calcium are closed. Potassiujm ions diffuse out of the cell making the inside of the cell more negative; at rest the potential difference across the plasma membrane is -70mV

• When glucose concentration outside the cell increases glucose molecules move into the cell

• The glucose is quickly used up in metabolism to produce ATP, which involves the enzyme glucokinase

• The extra ATP causes the potassium channels to close

• Potassium is no longer diffusing out of the cell which causes the cell to become less negative inside

• This change in potential difference causes the calcium ion channels to open

• Calcium ions enter the cell and cause the secretion of insulin by making secretory vesicles containing insulin to move to the plasma membrane and fuse with it and release insulin by exocytosis