BSI 2 Lecture 51: Pancreas Flashcards
What 2 major tissue types make up the pancreas?
exocrine acini and islets of langerhans
What 3 cell types make up the islets?
Alpha, beta, and gamma cells
Which islets cell is the most numerous?
beta cells (60%)
What happens in muscle cells when there is a high plasma insulin level?
Muscles uptake glucose and amino acids. They make glycogen and proteins
What happens in adipocytes when there is a high plasma insulin level?
increased glucose uptake and utilization and triglyceride synthesis
What happens in the liver when there is a high plasma insulin level?
increased glucose uptake, glycogen synthesis, and triglyceride synthesis
What happens in muscle cells when there is a low plasma insulin level?
Decreased glucose uptake, glycogen catabolism, protein catabolism, amino acid release, and fatty acid uptake and utilization
What happens in adipocytes when there is a low plasma insulin level?
Decreased glucose uptake, triglyceride catabolism, and release of glycerol and fatty acid
What happens in liver cells when there is a low plasma insulin level?
Increased glucose release and increased ketone synthesis and release
Does glucagon act in the opposite way of insulin?
It’s really just the difference in increased and decreased insulin because glucagon doesn’t have a lot of effect on muscle and adipose tissue
Is most insulin in the blood bound or unbound, and what does that do to the half-life?
Most of it is unbound which gives it a shorter half-life of about 6 minutes
Are the endocrine cells of the pancreas controlled by the hypothalamus?
No, they are controlled by changes in blood composition (short feedback loop)
What mechanism does insulin use to target proteins?
RTK’s
What cells does insulin bind to in order to stimulate glucose uptake?
Muscle cells and adipose cells
Does insulin affect neurons?
No, the brain is insulin dependent
How does increased plasma glucose cause beta cells to release insulin?
glucose enters the cell the GLUT-2 receptors where is it converted to ATP. This increases intracellular ATP and closes the ATP/K+ channel. Intracellular K+ levels decrease which depolarizes the cell. This causes an influx of calcium which stimulates vesicle exocytosis and secretion of insulin
What factors stimulate the release of insulin?
1) glucose (primary)
2) amino acids
3) fatty acids
4) GIT hormones
5) Parasympathetic nerves
6) Amylin
7) Glucagon (A cells)
8) Sulfonylureas
What factors inhibit the release of insulin?
1) Sympathetic nerves
2) B cells (negative loop)
3) D cells (Somatostatin)
Describe the two “wave” release of insulin.
When the levels up blood glucose are sustained at 3x the normal rate, there is a quick surge of insulin release followed by a decreased released and then another surge of extended release. This happens because there are vesicles of insulin ready to be released, but once these are depleted, more insulin has to be made. This causes the second surge of insulin.
What are the main counter-regulatory hormones to insulin?
1) glucagon
2) adrenaline
3) glucocorticoids
4) growth hormone
Why do resting muscle cells utilize FAs for energy?
Because their membranes aren’t very permeable to glucose without insulin
How does insulin promote uptake and storage of glucose?
It inhibits the liver phosphorylase that breaks down glycogen, increases the activity of enzymes that are involved in glycogen synthesis, and it alters glucose to a membrane-impermeable phosphate that becomes trapped
What percentage of glucose from a meal is stored as glycogen?
60%
