Pancreas and Blood Glucose Control:
The pancreas acts as both an endocrine and exocrine gland.
The pancreas therefore contains endocrine and exocrine tissue.
The endocrine tissue (Islet of Langerhans) contains beta cells
that secrete insulin and alpha cells that secrete glucagon and
has blood capillaries passing through for these hormones to be
secreted into.
The exocrine tissue (Acinus) secretes pancreatic juice
containing enzymes (e.g. amylase, lipases, proteases) and bile
into the pancreatic duct.
Insulin release:
1) The potassium channels into a beta cell are normally open,
whereas the calcium channels are normally closed.
2) Potassium ions diffuse out of the cell causing the inside to
become more negative (-70mV) than the outside.
3) As glucose concentrations outside of the cell increase,
glucose moves into the cell via diffusion.
4) Under the influence of the enzyme glucokinase, glucose is
metabolised to produce ATP.
5) The generation of extra ATP causes the potassium channels
to close.
6) The potassium ions now remain within the cell, and this
causes the inside to become less negative.
7) The insulin is packaged into vesicles and these vesicle move
towards the plasma membrane.
8) The vesicles fuse with the plasma membrane and release
insulin via exocytosis.
9) The insulin travels in the blood to the target cells.
Insulin increases permeability of the plasma membrane to
glucose.
The pancreas acts as both an endocrine and exocrine gland.
The pancreas therefore contains endocrine and exocrine tissue.
The endocrine tissue (Islet of Langerhans) contains beta cells
that secrete insulin and alpha cells that secrete glucagon and
has blood capillaries passing through for these hormones to be
secreted into.
The exocrine tissue (Acinus) secretes pancreatic juice
containing enzymes (e.g. amylase, lipases, proteases) and bile
into the pancreatic duct.
Insulin release:
1) The potassium channels into a beta cell are normally open,
whereas the calcium channels are normally closed.
2) Potassium ions diffuse out of the cell causing the inside to
become more negative (-70mV) than the outside.
3) As glucose concentrations outside of the cell increase,
glucose moves into the cell via diffusion.
4) Under the influence of the enzyme glucokinase, glucose is
metabolised to produce ATP.
5) The generation of extra ATP causes the potassium channels
to close.
6) The potassium ions now remain within the cell, and this
causes the inside to become less negative.
7) The insulin is packaged into vesicles and these vesicle move
towards the plasma membrane.
8) The vesicles fuse with the plasma membrane and release
insulin via exocytosis.
9) The insulin travels in the blood to the target cells.
Insulin increases permeability of the plasma membrane to
glucose.
