Lecture 36 Flashcards
During starvation what needs to occur and what hormone does this?
During starvation we need to supply the brain with fuels (120g of glucose per day), supply other tissues with fuels (mainly fatty acids), conserve protein as much as possible (to maintain structure and function) . The main hormone involved in all of this is glucagon (produced by alpha cells in pancreas when blood glucose drops).
Where does our energy for starvation come from?
We use roughly 10000 KJ of energy per day. This can be supplied by the breakdown of our energy stores, mediated by glucagon and adrenaline (roughly 15 kg of fat, x 37 KJ/g gives us at least 400000 KJ). The liver glycogen is mobilised back to glucose, stimulated by glucagon and providing enough fuel for the brain for a day.
How does glycogenolysis occur?
Glycogenolysis breaks down glycogen to glucose via the pathway: phosphorylase breaks it down into glucose 1-phosphates (adds phosphate as it does so), this is transformed to glucose 6-phosphate (via mutase in an equilibrium reaction) and then to glucose (via glucose 6-phosphatase). It can’t escape the cell until the phosphate is removed.
What does gluconeogenesis use and where does it occur?
Gluconeogenesis occurs mainly in the liver (also kidney cortex), it is the synthesis from glucose from lactate (muscle glycogen), alanine from muscle protein, glycerol from adipose tissue . It is once again stimulated by glucagon and is done via fatty acid oxidation (cannot be used to make the glucose, only supplies the energy) to provide the energy and most of the glucose produced this way goes to the brain.
What three pathways can glucose for the brain come from? How much?
We can mobilise about 200g of triacylglycerol a day (8000 KJ/day), this provides about 20g of glycerol (20g of glucose). The brain however needs 120g, the rest can come from proteolysis (not to much or all will be used up within 2-3 week) and ketone bodies like beta-hydroxybutyrate and acetoacetate.
What happens to levels of relative molecules in the blood over fasting time?
B-hydroxybutyrate and acetoacetate blood levels rise as days fasting increases, glucose levels are relatively constant (decreases until is plateus 2-3 days in) and free fatty acids are relatively constant (increases until it plateaus roughly 2-3 days in).
What are ketone bodies used for and how are they produced?
Ketone bodies are synthesised in the liver from fatty acids, beta oxidation forms acetyl-CoA, ketogenesis produces acetoacetate and this is in equilibrium with B-hydroxybutyrate. These can be used by the starving brain as an energy source via conversion back to acetyl-CoA. This can help to preserve protein.
