Early Starvation Flashcards
(37 cards)
Starvation begins at the end of the ______ period. What does this mean?
Postabsorptive period. All the food is digested and no substances are coming in from the gut.
During starvation, the body becomes reliant on ____ and _____.
Blood and stored fuels.
What do we store a lot of energy as but not use as a source of energy in starvation? Why?
Protein. There is a limit to how much of it we can break down before we die.
Keep blood glucose at ____mM. Known as ______.
5mM. Euglycemia.
The brain can only use what as fuel under normal circumstances? How much does it use?
Glucose. 120g a day.
Why cant the brain use FA?
Cant cross the blood-brain barrier
How is the main energy source of the brain transported in?
GLUT-1 transporters.
We store most of our energy as _____. But it cant be converted into _______. Why?
Fat. Carbohydrates. Pyruvate to acetyl CoA is irreversible and Acetyl CoA cant be made in glucogenic precursors.
Which parts of the body can exclusively use glucose?
Kidney, Skin and RBC
Which parts of the body can switch to FA as an alternate fuel during starvation?
Other tissues (not brain) ie muscle.
What is the general strategy in the early stages of starvation?
Glucose conservation
Glucose recycling - don’t fully oxidise it - regenerate from lactate
De novo glucose formation (make it from other things).
What happens during the first few hours of starvation?
All the tissues are using glucose. Blood glucose concentration falls
How is hypoglycemia prevented in early starvation?
The liver releases glucose into the bloodstream.
What is glycogenolysis?
Catalyses an equilibrium across the liver cell membrane so glucose concentration in liver cells and blood the same (Through GLUT 2 transporters)
What does an equilibrium across the liver cell membrane and blood signal to the liver cells?
Glucose release comes from glycogen stored in the liver (glycogenolysis - breakdown of the molecule glycogen to glucose)
What is the enzyme that breaks down glycogen in glycogenolysis? How does this occur?
Phosphorylase (rate-limiting step). Phsosphoylase cleaves terminal glycogen molecules to make glucose-1-phosphate which phosphorylates to G-6 - phosphatase.
What happens in glycogenolysis after G-6-Phosphatase is formed?
It is trapped in the cell (too big to leave) so it is transformed into glucose so it can be released by the GLUT-2 transporter into the bloodstream.
Which part of the glycogen molecule is attacked by the enzyme in glycogenolysis?
The end terminal units - the glyosidic link.
How is phosphorylase regulated?
By reversible phosphorylation - only active when phosphorylated by phosphorylase kinase.
What is the chain of events for the regulation of enzymes after phosphorylase?
Card 13
Why is the process of glycogenolysis so complex?
Amplifies signal
More control
What are branch points?
Points in a metabolic pathway in which a compound can be used as a substrate in two or more reactions. The cell must decide which of the pathways to direct the molecule to.
What does a debranching enzyme do to glucose at the branching point? Why?
Releases 10% of the glucose residues as neat glucose instead of G-6-Phosphate. Branching occurs every 10 residues.
Does muscle contribute to euglycemia?
Muscle does not break down glycogen much in starvation because it has no glucagon receptors and no glucose-6-phosphatase (cant release glucose into the blood).
