Week 4: Endocrine pancreas Flashcards
(56 cards)
Exocrine pancreatic cells
Acinar cells (digestive enzymes)
Duct cells (HCO3-)
Endocrine pancreatic cells
Islets of langerhans
Identify structures and functions
Identify histology of islets of Langerhans histology cartoon
Insulin function
tells cells to take up glucose (such as skeletal muscle through GLUT 4)
Insulin counter hormone
Glucagon
Insulin secreted by
β cells of the pancreas
What is the normal fasting range of glucose?
70-110 mg/dL
What secretes somatostatin?
D cells of the pancreas
What secretes glucagon?
α-cells of the pancreas
Explain what is happening here
- fasting level of glucose goes up after a meal to around 130 or 140 mg/dL and it slowly declines back to basal levels due to glucose going into cells where it is utilized or stored.
- Insulin is secreted by β cells of the pancreas in response to the rise in glucose levels in the blood after a meal
- Insulin never drops to 0 it always is there even in the fasting state
- Glucagon is high during the fasting state and it spikes but then goes way down to basal levels after a meal
- After fasting for a while glucagon levels will rise to fed state levels
Insulin and glucose are?
counter-hormones secreted by the pancreas
What happens when blood glucose level is high to the pancreatic hormones
- after a meal the β cells of the pancreas respond to high glucose levels and secrete insulin
- α- cells respond to the high glucose levels and stop secreting glucagon
what is in the center of the islet of langerhans?
β-cells
Describe the blood supply of the islet of Langerhans
there is a central artery so the β-cells respond first because they are in the center of the islet
How is pancreatic secretion regulated
- paracrine regulation
- Insulin inhibits secretion of glucagon from the α cells
- This all has to do with the architecture of the islet of Langerhans
- So the β cells actually control insulin and glucagon levels
Describe what happens in the fasting state
low blood glucose slows insulin secretion which stops inhibiting glucagon so the α cells can start secreting glucagon again
Catabolic state hormone
Glucagon
Anabolic state hormone
Insulin
Identify the mechanism of insulin synthesis
Describe the synthesis of insulin
- mRNA from Preproinsulin gene
- Synthesis of preproinsulin (excision of the signal peptide and a disulfide bond is formed)
- Transport of proinsulin to the Golgi where it is cleaved into insulin and is packaged into vesicles
- Mature insulin is ready for signaling in storage vesicles
Describe the molecular structure of insulin
- 2 disulfide bonds
- cleavage of the proform of proinsulin (2 endoproteases) releases the mature insulin which is the A chain and the B chain which is held together by a disulfide bond
- The disulfide-linked A and B chain is the mature form of insulin
How do β cells sense glucose?
- in the β cell, GLUT 2 glucose transporter facing the blood
- Glucose enters
- oxidized through glycolysis, TCA cycle and electron transport
- Creating a high ATP>/>ADP ratio
- ATP dependent K+ channel (normally allows the passage of K+ outside the cell) When ATP binds to the channel, it is inhibited from transporting so a + charge builds in the β cell
- There is a voltage-gated Ca2+ channel which responds to the difference in charge and lets Ca2+ into the cell
- The Ca2+ activates transport of insulin storage vesicles to the membrane to let insulin into the blood
What are Sulfonylurea drugs?
They target β cells ATP dependent K+ channels and act like ATP
It mimics the glucose-sensing system of the β cells to get insulin into the circulation
