Know the general mechanisms of hormone action with an example of each.
"Top Down" hormonal action: central nervous system recieves an input from internal and external systems and creates a production of hormonal signals. Cortisol for example is released in response to stress detected by the CNS. Hypothalamus recieves and integrates messages from the CNS, releasing factors that pass to the pituitary gland, which secretes hormonal factors that trigger the release of cortisol by the adrenal gland.
"Bottom Up" hormone systems send signals back to the brain and other tissues. For example Leptin (adipokine) is released when the adipose tissue is well-filled with Triacylglycerides, indicating the brain to inhibit feeding behavior.
Understand the Metabolic pathways that occur in the liver. Glucose 6-phosphate
Understand the metabolic pathways that occur in the liver. Amino Acids
Understand the metabolic pathways that occur in the liver. Fatty Acids
Know the energy sources for muscle contraction.
At rest, primary fuels are free fatty acids from adipose tissue. Light activity uses blood glucose in addition to fatty acids. Fast-twitch muscle uses stored muscle glycogen, break it down into lactate by fermentation, and yield 3 ATP (sparing 1 normally consumed by hexokinase because G6P is produced by phosphorolysis). During heavy exercise, phosphocreatine can rapidly regenerate ATP from ADP by the creatine kinase reaction.
Know the fuel sources available to the brain
Neurons normally only use glucose as fuel, and more than 90% of ATP produced in the neurons comes from oxidative phosphorylation. When the brain cannot directly use FFAs or lipids from the blood for fuel, they can get up to 60% of their energy needs from the oxidation of B-hydroxybutyrate (a ketone body) formed in the liver from FFAs.
Be able to describe the differences that occur in global metabolism following a meal.
After a meal, blood glucose levels rise, insulin increases which stimulates glucose uptake, phosphorylation, and oxidation via glycolysis and the citric acid cycle. Activates glycogen synthase in the liver and inactivated glycogen phosphorylase, so that much of the glucose 6-P is derived from blood glucose is channeled into glycogen. This stimulates the storage of excess fuel as fat in adipose tissue. The glucagon levels decrease, and the blood glucose finally decreases
Be able to describe the differences that occur in global metabolism a few hours after a meal.
Blood glucose returns to fasted in 2 ours, tissues receive glucose released from liver glycogen, and there is little to no synthesis of of TAGs. Blood glucose is restored by: simulating glycogen breakdown, preventing glycolysis, and promoting GNG. Decrease in glucose, decrease in insulin secretion , TAGs mobilized, FAs mobilized, converted to ketone bodies for export.
Be able to describe the differences that occur in global metabolism during prolonged fasting.
Muscle proteins are degraded to amino acids, undergo transamination to pyruvate. Decrease in insulin secretion, increase in glucagon secretion, glycogen broken down for glucose. Ketone bodies produced in starving conditions.
Describe how glucose controls insulin secretion by the pancreas.
When blood glucose rises, GLUT2 transporters carry glucose into the B-cells where it is immediatley converted to G6P by glucokinase and enter glycolysis. With the higher rate of glucose catabolism, ATP concentrations increase, causing potassium channels to close. Reduces potassium efflux depolarizes the membrane, and opens the Ca2+ channels, resulting in an increase in cytosolic Ca2+ concentration that triggers the release of insulin by exocytosis. (Glucose moves into pancreatic beta cell, inhibiting potassium channel, causing depolarization, allowing high concentrations of calcium ions to enter the cell stimulating insulin secretion). Reduced blood glucose is detected by the beta cell as a diminished flux through the glucokinase reaction; slowing or stopping the release of insulin.