October 16, 2023 Flashcards
is there neural innervation of pancreas beta cells
norepinephrine part of the sympathetic drive is secreted on beta cells of the pancreas
what does secretion of norepinephrine do to beta cells of pancreas
inhibits secretion of insulin
the more norepinephrine increases the more insulin goes down
why does insulin decrease with prolonged exercise
insulin decreases because sympathetic drive increases (norepinephrine part of sympathetic drive)
can training decrease norepinephrine’s inhibitory effect on insulin
yes
it reduces it effects (see graphs on page 60)
what is the optimal number for blood glucose levels in mM
5 mM
5+ mM = diabetic
less than 5 mM = hyperglycemic
how does the liver regulate glucose output
The liver regulates the release of glucose into the bloodstream based on the body’s energy needs and the prevailing hormonal signals. Hormones like insulin (which lowers blood glucose levels) and glucagon (which raises blood glucose levels) play a key role in signaling the liver to release or store glucose.
(Page 61)
how do muscles take up blood glucose
via GLUT4 transporter
what activates GLUT4
insulin (at rest) not during exercise
during exercise, insulin is not required to stimulate glucose uptake
does glucose uptake increase or decrease over long durations of time at 50% VO2 max
decrease, due to increase in Free fatty acid metabolism (FFA)
(page 61)
does glucose OUTPUT increase or decrease over long durations of time at 50% VO2 max
decrease
(page 61)
explain the mechanism for increased glucose uptake by insulin
Insulin Receptor Binding
Activation of Insulin Receptor
Insulin Signaling Cascade
GLUT4 Translocation: One of the key downstream effects of insulin signaling is the translocation of glucose transporters, primarily GLUT4, from intracellular vesicles to the cell membrane. GLUT4 is a glucose transporter protein that is responsible for facilitating glucose entry into the cell. In the absence of insulin, GLUT4 is mainly located in intracellular vesicles.
Increased Glucose Uptake: With GLUT4 now present on the cell membrane, it can transport glucose from the bloodstream into the cell. This results in increased glucose uptake and a reduction in blood glucose levels.
Glycogen Synthesis and Glycolysis: Inside the cell, glucose can be used for various metabolic processes, including glycogen synthesis in muscle and liver cells and glycolysis, which generates energy (ATP).
explain the mechanism for increased glucose uptake by exercise
Exercise increases glucose uptake by muscles through a mechanism that does not rely on insulin. This is especially important for maintaining blood glucose levels during physical activity when there may be an increased demand for energy. The mechanism for increased glucose uptake by exercise involves several key steps:
Muscle Contractions: When you engage in physical activity and your muscles contract, it initiates a signaling cascade that leads to increased glucose uptake. Muscle contractions themselves are a stimulus for this process.
AMP-Activated Protein Kinase (AMPK) Activation: Muscle contractions lead to an increase in the AMP-to-ATP ratio within muscle cells. AMPK is a cellular energy sensor that becomes activated in response to this increase in the AMP-to-ATP ratio, signaling a state of low energy availability.
Translocation of GLUT4: Similar to the action of insulin, AMPK activation results in the translocation of GLUT4 glucose transporters from intracellular vesicles to the cell membrane. This allows GLUT4 to transport glucose from the bloodstream into the muscle cells.
Glucose Uptake: With GLUT4 on the cell membrane, glucose can enter the muscle cells and be used for energy production during exercise.
Glycolysis and Oxidative Phosphorylation: Once inside the muscle cells, glucose can be metabolized through glycolysis and oxidative phosphorylation to produce ATP, providing the necessary energy for muscle contractions.
Insulin-resistant states (i.e. Type II diabetes, obesity) are characterized by elevated (blood glucose), as well as having issues with:
Glut 4
insulin receptors
insulin signaling cascade
is Glucose uptake insulin-independent or insulin-dependent during exercise
insulin-independent
Exercise has 3 beneficial health effects on glucose metabolism and insulin action:
- Acute exercise: induced increase in Glut4 translocation to the membrane from the exercise-sensitive Glut4 pool of transporters. (this can occur even in subjects with insulin resistance)
- Post-acute exercise recovery: induced increase in insulin sensitivity due to more Glut4 molecules in the plasma membrane, lasts about 24 hours
- Robust increase in insulin sensitivity, due to training: induced increase in Glut4 expression
(page 64)
